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Effects of Nitrogen Oxides on the Production of Reactive Oxygen Species and Environmentally Persistent Free Radicals from α-Pinene and Naphthalene Secondary Organic Aerosols
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A: Aerosols; Environmental and Atmospheric Chemistry; Astrochemistry

Effects of Nitrogen Oxides on the Production of Reactive Oxygen Species and Environmentally Persistent Free Radicals from α-Pinene and Naphthalene Secondary Organic Aerosols
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Cite this: J. Phys. Chem. A 2022, 126, 40, 7361–7372
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https://doi.org/10.1021/acs.jpca.2c05532
Published October 4, 2022

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Abstract

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Reactive oxygen species (ROS) and environmentally persistent free radicals (EPFR) play an important role in chemical transformation of atmospheric aerosols and adverse aerosol health effects. This study investigated the effects of nitrogen oxides (NOx) during photooxidation of α-pinene and naphthalene on the EPFR content and ROS formation from secondary organic aerosols (SOA). Electron paramagnetic resonance (EPR) spectroscopy was applied to quantify EPFR content and ROS formation. While no EPFR were detected in α-pinene SOA, we found that naphthalene SOA contained about 0.7 pmol μg–1 of EPFR, and NOx has little influence on EPFR concentrations and oxidative potential. α-Pinene and naphthalene SOA generated under low NOx conditions form OH radicals and superoxide in the aqueous phase, which was lowered substantially by 50–80% for SOA generated under high NOx conditions. High-resolution mass spectrometry analysis showed the substantial formation of nitroaromatics and organic nitrates in a high NOx environment. The modeling results using the GECKO-A model that simulates explicit gas-phase chemistry and the radical 2D-VBS model that treats autoxidation predicted reduced formation of hydroperoxides and enhanced formation of organic nitrates under high NOx due to the reactions of peroxy radicals with NOx instead of their reactions with HO2. Consistently, the presence of NOx resulted in the decrease of peroxide contents and oxidative potential of α-pinene SOA.

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Published as part of The Journal of Physical Chemistry virtual special issue “Advances in Atmospheric Chemical and Physical Processes”.

Introduction

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Atmospheric aerosols play an important role in climate, atmospheric chemistry, and public health. (1−5) Organic aerosols account for 20–90% of the total aerosol mass in the troposphere. (6,7) They can either be directly emitted into the atmosphere or be generated through oxidation of volatile organic compounds (VOC) by ozone (O3), hydroxyl radicals (OH), and nitrate radicals (NO3), followed by nucleation or condensation of semivolatile and low volatility products to form secondary organic aerosols (SOA). (8,9) The chemical composition of SOA can vary widely based on the environments in which they are formed. It has been well studied that the presence of nitrogen oxides (NOx = NO + NO2), emitted mainly from vehicular exhaust in urban air, can modulate gas-phase chemistry and chemical composition of SOA significantly. (10−14)
The OH oxidation of VOC is initiated by either abstraction of hydrogen or addition of OH to a C═C double bond, followed by the addition of molecular oxygen to generate peroxy radicals (RO2). Peroxy radicals have a number of reaction pathways with hydroperoxy radicals (HO2), nitrogen monoxide (NO), nitrogen dioxide (NO2), and other peroxy radicals (RO2). They can also undergo isomerization by internal hydrogen shift followed by molecular oxygen addition, so-called autoxidation. (15,16) The fate of RO2 and reaction products is strongly affected by the level of NOx: organic hydroperoxides (ROOH) are major reaction products as generated by reactions with HO2 or autoxidation to form highly oxygenated organic molecules (HOM) under low NOx, (17) while organic nitrates as well as carbonyls are expected to form by reactions with NOx under high NOx.
Reactive oxygen species (ROS) including hydrogen peroxide (H2O2), superoxide (O2•–), hydroxyl radical (OH), hydroperoxy radical (HO2), and organic radicals are contained within aerosols, triggering chemical transformation of aerosols in the atmosphere and oxidative stress upon respiratory deposition. There are growing numbers of studies to measure oxidative potential of particulate matter, (18) which may represent the redox activity for generation of ROS. (19,20) Previous studies have shown that ROS can be generated by aqueous reactions of SOA components such as decomposition of ROOH to generate OH followed by a cascade of aqueous reactions involving alcohols to generate superoxide. (21,22) Inhalation and respiratory deposition of SOA can lead to ROS generation in lung lining fluid, and excess ROS may cause oxidative damage and stress, inflammation, biological aging, and cell death. (23−26) Previous research indicated that aqueous-phase OH production is reduced in the presence of NO2. (27) A study by Chowdhury et al., which generated SOA under low and high NOx conditions in an oxidative flow reactor with ∼3 days of equivalent atmospheric aging, reported that NOx had no effect on ROS or total peroxide contents for naphthalene SOA, while NOx increased ROS generation with no effect on total peroxide content in α-pinene SOA. (28) Our study follows up these studies by investigating ROS formation from chamber-generated SOA with atmospheric aging on the hour scale.
In addition to production of ROS, which are relatively short-lived due to their highly reactive nature, SOA derived from aromatic precursors are observed to contain stable and long-lived radicals, so-called environmentally persistent free radicals (EPFR). (29,30) EPFR have longer lifetimes from minutes, months, and even indefinite in the atmosphere. (31−34) Naphthalene and other polycyclic aromatic compounds can produce EPFR upon oxidation to form semiquinone radicals, which are redox-active to produce ROS. (27,35) Only a handful of studies have investigated the effects of NOx on EPFR production. Gehling and Dellinger suggested that NO2 has the potential to decrease ROS production from EPFR in ambient air, while NO has little to no effect. (27)
Electron paramagnetic resonance (EPR) spectroscopy is an analytical technique that can be used to directly measure radicals. (10,36) In this study, we investigate ROS formation by SOA generated from representative anthropogenic and biogenic VOC precursors, naphthalene and α-pinene, respectively, under low and high NOx conditions to evaluate the effects of NOx on EPFR and ROS formation from SOA through EPR analysis. In addition, high-resolution mass spectrometry was used to determine chemical composition of SOA generated in high and low NOx environments. We also simulated the chemical composition of α-pinene SOA using an explicit gas-phase chemistry model (GECKO-A) and the radical two-dimensional volatility basis set (r2D-VBS) to estimate the distribution of functional groups in SOA.

Materials and Methods

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Secondary Organic Aerosol Generation

SOA particles were generated from the photooxidation of naphthalene or α-pinene with or without the presence of NOx in an environmental chamber. The chamber consists of a 5 m3 Teflon bag surrounded by a bank of 42 UV-B lamps with an emission spectrum centered at 310 nm, equipped with a scanning mobility particle sizer (SMPS) (TSI model 3936 classifier and model 3775 condensation particle counter) to monitor particle size distributions as well as an ozone monitor (Thermo Scientific model 49i) and an NOy monitor (Thermo Scientific Model 42i-Y). SMPS, NOy, and ozone data are available online at the Index of Chamber Atmospheric Research in the United States (ICARUS). (37) Before the injection of VOC and oxidant, the chamber was humidified to about 40%. The experiments were conducted at ambient temperature, which was 21 ± 2 °C for the duration of all experiments, with most of the variation being from heating by the lamps, which also reduced the relative humidity (RH) by several percentage points. Experiments were performed by injecting 2000 ppb of H2O2 as the OH precursor followed by 200 ppb of naphthalene or 500 ppb of α-pinene through a heated inlet. The steady-state OH concentration was estimated to be ∼1.4 × 106 molecules cm–3, similar to previous work. (38) For the high NOx experiments, 700 ppb of NO was added. No additional VOC, H2O2, or NO was added after the start of the experiment. Photooxidation was performed for 3.0 ± 0.5 h for all experiments for consistency. SOA particles were then collected on a 0.2 μm PTFE filter (Merck Millipore Ltd., part number FGLP04700) at a flow rate of 20 L min–1. The mass difference of the filter before and after collection was used as the SOA collection mass for all mass corrected results. A molar mass of 200 g mol–1 was assumed for all SOA collected and used to calculate yield. (39)

EPFR and ROS

After sample collection, the filters were immediately analyzed for EPFR using a X-band continuous-wave electron paramagnetic resonance (EPR) spectrometer (Bruker, Germany). The EPFR concentrations were quantified using a calibration curve of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL). EPFR measurements were scanned over the field range of 3300–3700 G and recorded as an average of 10 scans. The parameters for EPFR measurements were as follows: an attenuation of 12 dB, a modulation amplitude of 1.0 G, a microwave power 12.62 mW, and a receiver gain of 40. For EPFR analysis the filter was placed into a quartz tube and then directly placed in the resonator. EPFR stability was tested by analyzing filters at 5–10 min intervals up to 1.5 h postcollection. The filter was then stored at −20 °C until used for ROS analysis. For ROS measurements, the filter was extracted in a 1 mL aqueous solution of 10 mM spin-trapping agent 5-tert-butoxycarbonyl-5-methyl-1-pyrroline-N-oxide (BMPO) (Enzo, >99%). The extract was then placed in a 50 μL capillary tube for EPR measurements. The samples were scanned over the field range of 3470–3560 G and averaged over 50 scans. The parameters for ROS measurements were the same as EPFR, except for the receiver gain set to 30. The Bruker SpinFit software was used to deconvolute the EPR spectra to quantify the concentrations of BMPO adducts with hydroxyl radical (OH), superoxide (O2•–)/hydroperoxyl radical (HO2), and carbon- and oxygen-centered organic radicals. (33,34)

Total Peroxide

A second set of chamber filters was generated for a total peroxide measurement and dithiothreitol (DTT) analysis. Peroxides can oxidize I– to form I2, which can then combine with I– to form I3–. Peroxides in solution can be quantified by the characteristic absorbance of I3– at 289 and 350 nm. A wavelength of 350 nm was used to quantify peroxide concentration in naphthalene and α-pinene SOA. Calibration was performed using 0.2–2 μM benzoyl peroxide (Sigma-Aldrich, ≥98%). SOA filters were extracted for 7 min in 1 mL of Milli-Q water. 100 μL of the SOA extract was combined with 700 μL of ethyl acetate (Sigma-Aldrich, 99.8%). The 800 μL solution was then mixed with 636 μL of acetic acid (Sigma-Aldrich, ≥99%), 324 μL of chloroform (Sigma-Aldrich, ≥99.5%), and 240 μL of Milli-Q water, forming a 2 mL solution. This solution was then purged of dissolved O2, which might also oxidize I–, by a N2 flow for 2 min. Afterward, 20 mg of potassium iodide (KI, Sigma-Aldrich, ≥99%) was added to the solution, and it was left to sit for 1 h. The absorbance was then measured at 405 nm using the GloMax Discover Microplate Reader. The total peroxide measurement method is based on the iodometric–spectrophotometric method used by Docherty et al. (40,41)

DTT Assay

Dithiothreitol (DTT) analysis was performed to measure the total oxidative potential and redox activity, (32,42) which is often assumed to correspond to ROS formation and to represent indicator of PM toxicity. (20) DTT analysis quantifies the consumption of DTT over time by redox-active or reactive compounds contained in SOA water extracts. The sample was extracted into 0.7 mL of Milli-Q water and combined with 0.2 mL of potassium phosphate buffer (pH 7.4) in the reaction vial. The vial was then incubated at 37 °C, and the reaction was initiated by adding 0.1 mL of 1 mM DTT. A 50 μL aliquot of the reaction vial was then mixed with trichloroacetic acid (TCA) to quench the reaction and different time points to note the oxidation over time. To analyze the sample, it was mixed with Tris buffer and 5,5-dithiobis(2-nitrobenzoic acid) (DTNB), which combines with the residual DTT to form a light-absorbing compound. The absorbance of this product was measured at 412 nm with the Liquid Waveguide Capillary Cell (LWCC) coupled to an online spectrophotometer (Ocean Optics, Inc., Dunedin, FL), consisting of an DT-Mini-2 ultraviolet– visible (UV–vis) light source and a USB4000 miniature fiber-optic spectrometer.

High-Resolution Mass Spectrometry (HRMS)

HRMS was used to analyze SOA chemical composition. SOA was extracted from the filters by shaking the filters in acetonitrile for 5 min. The solvent volume was chosen to achieve a concentration of SOA in acetonitrile of 400 μg mL–1 assuming 100% extraction efficiency. Then an equal amount of water was added so that the SOA concentration would be 200 μg mL–1 for HRMS analysis.
The instrument has been described previously in Chin et al. (43) A 10 μL aliquot of sample was injected into a Phenomenex Luna Omega Polar C18, 150 × 2.1 mm2 column, with 1.6 μm particles and 100 Å pores for ultrahigh performance liquid chromatography (UPLC) separation and photodiode array (PDA) detection. The PDA detector was followed by a Thermo Q-Exactive Plus mass spectrometer with a heated electrospray ionization inlet and a resolving power of 1.4 × 105 at m/z 400, which was operated in both positive (spray voltage +3.5 kV) and negative (spray voltage −2.5 kV) ion modes. (43) The UPLC solvents were water acidified to pH 3 with 0.1 wt % formic acid (solvent A) and acetonitrile acidified with 0.1 wt % formic acid (solvent B). The gradient was 95% solvent A and 5% solvent B for 3 min, followed by a linear ramp to 95% solvent B and 5% solvent A from for 11 min, a hold at 95% solvent B for 2 min, and finally a linear ramp back to 95% solvent A and 5% solvent B for 4 min in preparation for the next run.
FreeStyle 1.6 from Thermo Scientific was used to generate a raw time-integrated mass spectrum by integrating over the full total ion chromatogram (1–18 min). Peaks and their relative intensities were then extracted from the time-integrated mass spectrum using Decon2LS (https://omics.pnl.gov/software/decontools-decon2ls), and peaks representing 13C compounds were removed. Peaks from the solvent and SOA samples were then aligned with a tolerance of 0.0005 m/z, and peaks with equal or greater intensity in the solvent than in the samples were also removed. The resultant mass spectra were assigned within a tolerance of 0.0005 m/z to a formula of [CcHhOxN0–3 + Na]+ and [CcHhOxN0–3 + H]+ for positive ion mode and [CcHhOxN0–3 – H]− for negative ion mode. The internal calibration of the m/z axis in both ion modes was verified using the assigned peaks, and the calibration was adjusted where necessary. This internal calibration improved the m/z accuracy, leading to a few additional assignments for peaks that could not be assigned within 0.0005 m/z in the uncalibrated mass spectra. Neutral formulas were calculated from the assigned ions by taking into account the ionization mode, and the two modes were clustered together. The mass spectra and elemental ratios presented here refer to the combined peak abundance in the positive and negative ion mode data referenced to formulas of the un-ionized SOA compounds.

GECKO-A Model

We have conducted modeling of gas-phase chemistry and subsequent SOA formation using the Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) to perform an in-depth investigation of SOA functionality in particles. (44,45) GECKO-A is a detailed generator of gas-phase chemical mechanisms based on experimental data and observed structure–activity relationships (SAR). (45) It is coupled to a 0-D photochemical box model enabling the simulation of chamber experiments by treating gas-particle partitioning. Partitioning of oxidation products into the particle phase is treated based on their vapor pressures as estimated using the Nannoolal et al. approach. (46) GECKO-A does not account for gas-phase chemistry of species with vapor pressure below 10–13 atm, which are assumed to be nonvolatile in the condensed phase. The generator accounts for peroxyacyl (RC(O)O2) and peroxy (RO2) chemistry including reactions with NOx, HOx, and RO2. For the RO2 + HO2 reaction, the generator assigns a branching ratio of 80% to hydroperoxide formation and 20% to the creation of an alkoxy radical and the regeneration of another OH. GECKO-A is enriched with SAR estimations of alkoxy radical (RO) decomposition and H-migration reaction rates. (47) The HO2 chemical section also accounts for alkylperoxy radical reactions leading to the formation of hydroperoxides. Note that GECKO-A treats neither autoxidation, dimerization of RO2, nor particle-phase chemistry. Chemistry of peroxyacyl nitrates (PANs) is based on the SAR rules by Jenkin et al., covering the reactions of organic peroxy radicals. (48) There is a limited coverage of specific PAN reactions with −NO2 and −HO2, and therefore the species follow the SARs reactions pathways of other peroxy radicals. As GECKO-A chemical generator is not able to redact the chemical mechanisms of compounds with more than two double bonds, we were unable to perform an analysis on the functionality distributions of carbonyl groups in SOA produced by naphthalene.
GECKO-A and its photochemical box model have successfully simulated SOA formation by α-pinene photooxidation and dark ozonolysis. (49,50) In this study, we used GECKO-A photochemical box model to simulate α-pinene photooxidation under low and high NOx conditions to track the evolution in SOA functionality with the aim of establishing the dominant chemical routes occurring in our chamber experiments. The initial α-pinene mixing ratio was set to 500 ppb. The low NOx scenario includes a steady-state concentration of 1 ppb of NOx initially introduced as NO, representative of the background NOx mixing ratio in the chamber. NOx mixing ratios were fixed to 700 ppb for high NOx conditions. The OH concentration was fixed at 1.4 × 106 cm–3 to match the steady-state concentration calculated for similar experimental setups reproducing VOC photooxidation in the same chamber. (51) The RH and temperature were fixed at 38% and 294 K, respectively. Photolysis rates were computed for the photon flux of the UV light used to generate OH in the chamber experiments (250 < λ < 650 nm). As GECKO-A does not include particle nucleation, we assumed pre-existing particles to have a radius of 5 nm and an initial concentration of 10–4 cm–3. (49,50) The vapor wall loss is also considered with deposition rate constant of 5 × 10–3 s–1 based on previous experiments using similar chamber reaction volumes. (52,53) Functional group distributions in the particle phase were estimated based on the ratio between the total number of carbon atoms per molecule per specific functional group (CG) and the total number of carbon atoms measured in the particle phase (CTOT). (54)

Radical 2D-VBS

The radical 2D-volatility basis set model (r2D-VBS) has been described in detail in Schervish and Donahue, but a brief discussion is given here. (55,56) This model simulates gas-phase chemistry through representative peroxy radical (RO2) species and ultimately distributes these products into the 2D-VBS based on volatility or effective saturation mass concentration (C*) using semiempirical kernels for each radical termination reaction. Both autoxidation and dimerization of RO2 are included in this model, but due to the simplified chemical kinetics and grouping of RO2 species, specific functional groups on closed-shell products cannot be determined. However, autoxidation has been well-documented to lead to organic hydroperoxide (ROOH) formation. This model has previously been shown to reproduce trends associated with α-pinene oxidation under different conditions including addition of NOx. (55)
For this work, we run the model with an initial input of 500 ppb of α-pinene under both low and high NOx scenarios. The low NOx scenario includes a steady-state concentration of 1 ppb of NOx initially introduced as NO, representative of the background NOx mixing ratio in the chamber. In the high NOx scenario 700 ppb of NO is introduced and allowed to decay over time. NOx cycling was implemented, so most of the NO has been converted to NO2 at the end of the simulation. We prescribed an OH concentration of 1.4 × 106 cm–3. As this model typically underestimates HO2 due to the lack of small carbon-containing molecules that promote conversion of HO2 to OH, we prescribed an HO2 concentration of 1 × 108 cm–3. (56) We used a wall loss time scale of 1 h for all species. This is to achieve similar product concentrations as seen in the GECKO-A model runs. The time scale used is longer than that used in the GECKO-A simulation as GECKO-A incorporates resuspension of gases from the walls. In addition, the radical 2D-VBS does not include any dynamic gas-particle partitioning, and thus there is no competitive process to wall loss and necessitates wall loss being slower to reach similar concentrations as GECKO-A simulations. To estimate the ROOH concentration in the particle phase, we only included VBS bins which contribute to particles when 200 μg m–3 of organic aerosol is present. This leads to 2/3 of the C* = 100 μg m–3 bin and 1/6 of the C* = 1000 μg m–3 bin being included. All molecules in bins with C* < 100 μg m–3 were included, and none were included from bins with C* > 1000 μg m–3.

Results and Discussion

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Environmentally Persistent Free Radicals

Naphthalene SOA showed a significant EPFR signal, while no EPFR signal was observed for α-pinene SOA. This is expected as products of α-pinene oxidation are mostly ring-opened molecules without extensive conjugation and thus do not lead to EPFR formation. Naphthalene is the simplest form of polycyclic aromatic hydrocarbons (PAHs), (57) which are known to be precursors of EPFR as their oxidation products are expected to retain aromatic or conjugated structures that would stabilize unpaired electrons. (29,58) The g factor of the EPFR signal in this study was around 2.0035 ± 0.0010. A previous study has suggested that g factor signals of 2.0035 ± 0.0004 signify carbon-centered (phenoxy) or oxygen-centered (semiquinone) radicals generated from PAH oxidation, so we expect the chemical identity of EPFR to be semiquinone- or phenoxy-type radicals as both radicals are reported to be produced by OH oxidation of naphthalene. (27,58,59)
As shown in Figure 1a, naphthalene SOA generated under both low and high NOx conditions exhibited similar concentrations of EPFR with ∼0.7 ± 0.5 pmol (μg SOA)−1. The EPFR concentrations were measured for seven SOA samples for each condition. The measurements were conducted after about 20 min of SOA collection completion, and EPFR concentrations were observed to decrease over time followed by flattening, as shown in Figure 1b. EPFR remained present at a lower concentration after 80 min and even after freezing overnight for some samples. While a previous study suggested that carbon-centered radicals are more stable than oxygen-centered radicals, (59) there was no change in the g factor over the course of the decay, indicating no significant changes in radical species. EPFR concentrations were similar between low and high NOx environments at each time point after 30 min with e-folding lifetimes of about 42 ± 5 min.

Figure 1

Figure 1. (a) EPFR concentrations in naphthalene SOA generated under low and high NOx conditions after 30 min of sample collection. (b) Decay of EPFR in naphthalene SOA generated under low (dark gray) and high NOx (light gray) conditions over the span of 80 min after SOA collection.

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From the high-resolution mass spectrometry data it is observed that nine of the ten most abundant compounds produced in the chamber under both low and high NOx conditions have identical chemical formulas for naphthalene SOA. Results of the high-resolution mass spectrometry data are shown in Table 1 of the HRMS section. The highest six compounds for naphthalene SOA appear in the same order with the same relative intensities (±6%) and exist as ring-retaining structures. Both sets of products display aromatic properties as calculated by their double bond equivalent (DBE) (see further details below). These findings of minimal variation between high and low NOx naphthalene SOA composition agree with a previous study. (58) As such, we would expect that EPFR are produced through the same route and with the same formation efficiency. Figure 2 shows the abundance of C10H6O2+ compounds, respective to their oxygen number (compounds may contain two or more oxygen atoms). C10H6O2+ compounds are assumed to be quinones, which are known precursors to EPFR. There is no discernible effect of NOx on the abundance of any oxygen-containing C10H6O2+ compounds. Therefore, in addition to the DBE, an equal amount of C10H6O2+ specifically may account for the comparable EPFR production between low and high NOx conditions. Note that naphthalene SOA under a low NOx environment produced more ring-retaining compounds such as naphthol, naphthoquinone, and epoxyquinone in the gas phase. Under a high NOx environment the major gas-phase products include ring-opening products such as 2-formyl cinnamaldehyde, phthaldialdehyde, and phthalic anhydride. (58) Further research is required to identify chemical identities of EPFR generated under low and high NOx conditions.

Figure 2

Figure 2. Abundance of C10H6O2+ compounds in naphthalene SOA as determined by high-resolution mass spectrometry.

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Table 1. Top Ten Peaks in Each SOA Formation Condition Listed by Relative Peak Abundance, Normalized to the Highest Peak in Each Spectrum, Including Their Neutral Mass and Assigned Neutral Formula
naphthalene low NOxnaphthalene high NOxα-pinene low NOxα-pinene high NOx
rel abundance (%)neutral mass (Da)formularel abundance (%)neutral mass (Da)formularel abundance (%)neutral mass (Da)formularel abundance (%)neutral mass (Da)formula
100134C8H6O2100134C8H6O2100182C10H14O3100166C10H14O2
86162C9H6O381162C9H6O395198C10H14O493172C8H12O4
79192C10H8O474174C10H6O382172C8H12O488198C10H14O4
77174C10H6O371176C10H8O381166C10H14O285138C8H10O2
57176C10H8O362192C10H8O474138C8H10O281182C10H14O3
56166C8H6O462166C8H6O470126C7H10O277126C7H10O2
55148C9H8O260189C10H7O3N66152C9H12O275168C9H12O3
49190C10H6O449190C10H6O463164C10H12O270186C9H14O4
48208C10H8O548150C8H6O362154C8H10O369124C8H12O1
40150C8H6O346148C9H8O260140C7H8O367122C8H10O1

Reactive Oxygen Species

Figure 3a shows that α-pinene SOA generated under the low NOx condition mainly generates OH radicals and superoxide, which is consistent with our previous study. (21) OH radicals can be generated by the decomposition of ROOH, and superoxide can be formed by OH oxidation of primary and secondary alcohols and unimolecular decomposition of α-hydroxyperoxy radicals. (21,22) In Figure 3b, naphthalene SOA generated under the low NOx condition shows the dominant superoxide formation, which is most likely generated via redox reactions of quinones. (28,29) The formation of organic radicals are relatively minor for both SOA.

Figure 3

Figure 3. Molar yields of BMPO radical adducts (BMPO-OH, BMPO-OOH, BMPO-OR, and BMPO-R) in water extracts of (a) α-pinene and (b) naphthalene SOA generated under low and high NOx conditions.

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For both naphthalene and α-pinene SOA generated under high NOx conditions, ROS production was diminished. For α-pinene SOA, the total radical yield (the percentage of moles of BMPO radical adducts to the total moles of SOA) decreased from ∼0.029% to ∼0.009%, with OH and superoxide formation decreased by a factor of ∼9 and ∼2, respectively. For naphthalene SOA, the total radical yield was reduced from ∼0.030% to ∼0.010%, with OH and superoxide reduction by a factor of ∼1.5 and ∼3.5, respectively. SOA extracts were slightly more acidic for high NOx SOA compared to low NOx SOA, consistent with Kautzman et al., who found an enhancement of acid formation for naphthalene SOA produced in a high NOx environment. (58) Note that our recent study showed α-pinene and naphthalene SOA generated under low NOx would have higher ROS production at lower pH, (60) but the influence of NOx has a greater effect on ROS yield than the pH of the system. A previous study has indicated that acid may reduce the formation of semiquinones, (27) which may contribute to the reduction of ROS formation.
Given ROOH is an important source of ROS, we have quantified peroxides using an iodometric spectrophotometric method. As shown in Figure 4a, α-pinene SOA generated under the low NOx conditions contained substantial amounts of peroxides (∼29 ± 11%), which decreased significantly by a factor of ∼2 for SOA generated under high NOx conditions. There was not a detectable amount of peroxide for naphthalene SOA. Given that organic peroxides are reported to contribute to oxidative potential, (61) we performed the DTT assay on both samples of naphthalene and α-pinene SOA, as shown in Figure 4b. Naphthalene SOA has a significantly higher DTT activity by a factor of 4 than α-pinene SOA, most likely due to redox activity of quinones contained in naphthalene SOA. (62) The oxidative potential is slightly higher for α-pinene SOA formed under low NOx compared to those under high NOx, while there is no significant difference for naphthalene SOA. It has been shown that DTT activity of α-pinene SOA is insensitive to NOx, (63) while NOx was reported to enhance oxidative potential of isoprene SOA. (61)

Figure 4

Figure 4. (a) Total peroxide concentrations and (b) DTT activities of α-pinene and naphthalene SOA produced under low and high NOx conditions. Error bars represent the standard deviation.

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SOA Modeling

For α-pinene oxidation, the fate and reaction pathways of peroxy radicals (RO2) are critical for SOA formation. There are competitions of NOx and HO2 to react with RO2 radicals leading to different products as follows:
RO2+NO→RONO2orRO+NO2
(R1)
RO2+NO2→ROONO2
(R2)
RO2+HO2→ROOH+O2
(R3)
Note that (R2) is only relevant for acylperoxy radicals (R–C(O)OO), and it is an equilibrium process. In addition, NOx can decrease the abundance of ROOH by suppressing autoxidation and the formation of HOM, which can be significant source of ROS. (64)
Figure 5a shows the SOA functional group distributions for simulated α-pinene photooxidation SOA under low and high NOx conditions by GECKO-A. Under low NOx, RO2 would mainly react with HO2 to form ROOH, accounting for 20% of carbon atoms, which is comparable to the measured peroxide yield of ∼29% (Figure 5a). 13% of carbon atoms are associated with alcohols (ROH). Under high NOx conditions, RO2 are terminated by NOx forming organic nitrates (RONO2), (40) and ROOH is expected to be very low. It is estimated that around 30% of carbon atoms would be associated with RONO2, in addition to around 25% associated with PANs. Note that PAN potentially decompose to additional peroxy radicals, (65,66) but this process is not treated in the model, which may lead to less alcohol predicted in the model than is observed experimentally. Slightly higher formation of ketone (RCOR) and aldehyde (RCHO) species is predicted under high NOx environments.

Figure 5

Figure 5. (a) Functional group distributions in α-pinene SOA simulated by the GECKO-A box model for the photooxidation of α-pinene under low and high NOx conditions. (b) Modeled concentrations of organic hydroperoxides and organic nitrates from α-pinene oxidation under low and high NOx conditions by r2D-VBS. The green bars represent OOH formation with an allowed production of one peroxide per molecule, whereas the blue bars represent OOH formation with OOH production at each step of autoxidation. The red bar represents the organic nitrate formation in the presence of NOx.

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As GECKO-A does not account for autoxidation, we applied the radical 2D-VBS model which considers autoxidation. Because specific functional group information about the oxidized SOA is unknown, we made assumptions about the −OOH groups present on the molecules. In the first case, it was assumed that every molecule that has undergone autoxidation has only one −OOH group that can decompose and lead to ROS formation (one OOH per molecule). In the second case, we counted every step of autoxidation a molecule has undergone as being an additional −OOH group that can decompose (total OOH per molecule). In both cases products from the RO2 + HO2 reaction were included regardless of degree of autoxidation (but were counted as an additional −OOH group in case 2). We included these cases as some ROOH may decompose prior to analysis, a process that is not accounted for in the model. While this model treats dimerization, it is unclear to what extent dimers may decompose or hydrolyze in aerosol; therefore, we only included their contribution to the total −OOH functionality if they underwent any autoxidation.
Figure 5b shows a clear reduction in the −OOH groups as a result of the addition of NOx, consistent with the results from GECKO-A. The percentage reduction in each case is between 95 and 98%. While the mechanism for the production of these hydroperoxides is different in these two models, the excellent agreement for the relative reduction due to the addition of NOx to the system provides evidence of this phenomenon occurring whether autoxidation is taking place and RO2 are primarily terminating with each other or if RO2 is primarily reacting with HO2. In reality, both of these termination reactions are occurring to different extents under different conditions depending on NO:HO2, but both are clearly repressed with the addition of NOx.
Figure 5b also shows the total organic nitrates formed in both scenarios. While termination with NOx is competitive under both scenarios, when NOx is present in small amounts, it does not totally dominate over autoxidation, allowing for the formation of some organic nitrates that have −OOH functionality due to prior autoxidation. However, under high NOx conditions, the RO2 + NO dominates autoxidation, leading to a marked decrease in hydroperoxide functionality. The organic nitrates alone do not totally compensate for the decrease in −OOH functionality because formation of organic nitrates from the reaction of RO2 + NO only accounts for 25% of the yield of this reaction in the model. However, as these species tend to be lower in volatility than the products formed from the alkoxy radical pathway within this model framework, the particle-phase organic nitrates account for much more than 25% of the particle phase yields. The increase in particle-phase RONO2 species by roughly a factor of 2 from the low to high NOx scenarios is also consistent with the results from GECKO-A.

High-Resolution Mass Spectrometry

We observed that both naphthalene and α-pinene SOA show significant incorporation of nitrogen under high NOx conditions as predicted by the GECKO-A and r2D-VBS model. As shown in Figure 6, the addition of NOx during SOA formation leads to the production of many nitrogen-containing compounds. There are also low abundances of nitrogen-containing compounds (CHON) formed under low NOx conditions (Figure 6a,c) as background levels of NOx in the smog chamber were around 1 ppb. While our mass spectrometry method does not provide individual functional group information, based on previous work, we expect the nitrogen-containing groups in the naphthalene SOA to be mostly nitroaromatics and in the α-pinene SOA to be organic nitrates (RONO2). (67,68) SOA composition agrees relatively well with previous work on α-pinene and naphthalene high and low NOx SOA. (69−72) Both SOA types have distinct monomer (approximately <250 Da) and dimer (250–500 Da) regions. The α-pinene SOA also has a small trimer region above 500 Da. The major peaks in both naphthalene SOA conditions generally have formulas of C8–10H6–8O2–5 (see Table 1 for the top 10 most abundant peaks in each spectrum). The major peaks in both α-pinene SOA conditions have formulas of C8–10H12–16O2–5. For the α-pinene SOA, there are also a few C7 compounds that are abundant and less typical of previously reported α-pinene SOA. These C7 compounds may be a result of in-source fragmentation due to the spray voltage being too high during mass spectrometry analysis. They are not evident in the aromatic naphthalene SOA, which should be less susceptible to fragmentation.

Figure 6

Figure 6. High-resolution mass spectra and intensity-normalized average elemental ratios for (a) naphthalene (NAP) low NOx SOA, (b) NAP high NOx SOA, (c) α-pinene (APIN) low NOx SOA, and (d) APIN high NOx SOA. Compounds containing only carbon, hydrogen, and oxygen (CHO) are shown in black while compounds containing carbon, hydrogen, oxygen, and nitrogen (CHON) are shown in red.

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Table 1 shows the top ten products for naphthalene and α-pinene SOA under high and low NOx conditions. Nine of the ten top naphthalene SOA products are shared for the high and low NOx environments. The two deviations for naphthalene SOA were C10H8O5 and C10H7O3N. The naphthalene high NOx environment saw the incorporation of nitrogen into the final product, forming a nitroaromatic. Only the top five out of ten α-pinene SOA products were the same for high and low NOx conditions. None of the remaining five products of α-pinene SOA in the high NOx environment included organic nitrates. In the complete product list for α-pinene SOA, organic nitrate compounds were present, agreeing with the aforementioned studies that show the formation of these compounds in a high NOx environment. Also, there may be fewer nitrogen-containing compounds measured by HRMS in the α-pinene SOA because some of the organic nitrates may have hydrolyzed in water before they were able to be analyzed; for instance, tertiary nitrates derived from isoprene have been estimated to have hydrolysis lifetimes of <10 s when dissolved in water. (73)
To look for evidence of changes in the reaction pathways described in chemical reactions R1–R3, specifically a reduction in peroxide functional group formation with the addition of NOx, we examined the double-bond equivalents (DBE) as a function of carbon number for the compounds that do not contain nitrogen, shown in Figure 7. Equation R3 predicts the formation of peroxide functional groups which have a DBE of 0. Under high NOx conditions, we expect (R1) to compete with (R3), leading to a carbonyl group with a DBE of 1. Therefore, if the addition of NOx reduces the formation of peroxides, the DBE distribution of the CHO compounds should show fewer low-DBE compounds under high NOx conditions. Looking at Figure 7a, this seems to be the case for naphthalene SOA. Some of the CHO compounds with low DBE which form under low NOx conditions are not formed under high NOx conditions. This pattern appears less evident for the α-pinene conditions, shown in Figure 7b, although there are some low-DBE peaks present under low NOx conditions which are not present under the high NOx conditions. The abundance of peroxide functionalities determined by the ROS measurements are also more similar between the low and high NOx conditions for α-pinene than for the naphthalene conditions, so our DBE comparison may not be sensitive enough to observe a shift for α-pinene SOA. Finally, the higher aromaticity of naphthalene, which is shown by higher DBE in Figure 7a, corroborates the EPFR results, as aromaticity is required for EPFR. (59)

Figure 7

Figure 7. Double-bond equivalents as a function of carbon number for (a) naphthalene SOA and (b) α-pinene. SOA formed under high NOx conditions, excluding nitrogen-containing compounds, is shown in red circles, and SOA formed under low NOx conditions is shown in black squares. Marker size is scaled to the relative summed intensity at each point.

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Discussion

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The experiments were conducted using high mixing ratios of α-pinene and NOx to produce enough material for the EPR and HRMS analysis. This limitation does not apply to the models, which can assume any starting conditions. By maintaining the same temperature, RH, and total absorbing organic aerosol mass, but with an α-pinene and NOx mixing ratio reduced to 200 ppt and 50 ppb, respectively, r2D-VBS predicts a reduction of −OOH functionality by a factor of 25 from the NOx-free condition. If we represent more pristine conditions with 50 ppt of NOx, the reduction of −OOH functionality is only 20% compared to the NOx-free condition. These percentages reflect only counting one −OOH group per molecule (case 1) because, as noted previously, the different methods give quite similar relative reductions. The reduction of −OOH functionality may be due to the fact that under 50 ppt NOx competitiveness of autoxidation is enhanced and may be dominant over that of a reaction with NO. In the chamber NO reacted quickly to form NO2. As there was an initial concentration of 700 ppb NO, it can be assured that enough NO remained in the chamber to make the reaction of RO2 with NO dominant over other loss processes. With 1 ppb or greater NO maintained in the chamber and equal amounts of RO2, the isomerization of RO2 with the first-order rate of ∼0.1 s–1 and the reaction of RO2 + NO are competitive. (48,74) Under 50 ppt NOx this may no longer be the case, and autoxidation will most likely be the major process, while RO2 can still undergo a reaction with NO.
The GECKO-A and 2D-VBS models predict the reduction of hydroperoxides under high NOx conditions. The formation of organic nitrates in the presence of NOx was predicted in both models, which can be interpreted as a competitive alternative pathway to hydroperoxide formation for the RO2 termination. The presence of organic nitrates under high NOx conditions was also confirmed experimentally using high-resolution mass spectrometry. The model outcomes, however, predicted a higher reduction by 92–98% in hydroperoxides than was observed experimentally in the reduction of O2– and HO2 by 25–75% and the reduction of OH by 70–90% for α-pinene SOA.
Because these models are both gas-phase models, the apparent discrepancy may be due to chemistry in the particle phase. In addition, particle-phase processes associated with nonideal mixing and particle phase state are not explicitly considered in these models. When particles adopt amorphous semisolid or glassy states, kinetic limitations of bulk diffusion can retard mass accommodation, heterogeneous reactions, and partitioning. (75−77) This may contribute to the potential overrepresentation of multifunctionalized NO2 and OH bearing compounds in the presence of NOx which can lead to production of more volatile compounds. (14) Moreover, the occurrence of liquid–liquid phase separation can also significantly impact SOA partitioning. (78) These aspects may warrant further investigations in future studies.
While organic hydroperoxides are regarded as a major ROS source, it is unclear if peroxyacetyl nitrates and other highly functionalized nitrates might contribute to ROS formation. Some of these compounds might decompose and through a series of subsequent reactions form the peroxy radical, contributing to the production of ROS. (65) Note that the GECKO-A model accounts for the decomposition of PAN in the gas phase; given there is little variation between GECKO-A and 2D-VBS, we do not expect this process to be a major process contributing to ROS formation.
Our results are in contrast with the findings from Chowdhury et al., where there was more ROS production from aged naphthalene and α-pinene SOA in the presence of NOx. Note that our study agrees with their finding that total peroxide production from aged α-pinene SOA decreases in the presence of NOx. (28) The discrepancy between these studies may be due to methodology. SOA in the Chowdhury study was generated in an oxidative flow reactor, with an aging period equivalent to 3 days in the atmosphere. Concentrations of naphthalene and α-pinene as well as NOx were on the same order of magnitude, but NOx was added as 2% NO2. Further studies are warranted to investigate ROS formation by SOA as a function of chemical aging time.

Conclusions

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In this study we measured EPFR and ROS associated with naphthalene and α-pinene SOA generated under low and high NOx conditions. We found that α-pinene SOA does not contain significant amounts of EPFR, while naphthalene SOA contains EPFR with a particle-mass-normalized concentration of ∼0.7 ± 0.5 pmol μg–1. EPR measurements show that NOx exhibits minimum impacts on EPFR production, and high-resolution mass spectrometry measurements indicate that there is also no discernible effect of NOx on the abundance of C10H6O2+ compounds, which are likely to be quinones which would produce EPFR. α-Pinene and naphthalene SOA generated under low NOx conditions mainly produce OH radicals and superoxide in the aqueous phase, which is suppressed substantially for SOA generated in the presence of NOx; the total radical yield decreased from 0.029% to 0.009% for α-pinene SOA and from 0.030% to 0.010% and for naphthalene SOA.
The reduction of ROS formation for SOA generated in the presence of NOx is due to suppression of the formation of organic hydroperoxides as indicated by peroxide measurements and the reduction of total oxidative potential as measured by the DTT assay. The GECKO-A modeling finds that RO2 is terminated by NOx forming organic nitrates (RONO2), and ROOH is expected to be very low under high NOx conditions. Further modeling by r2D-VBS, which considers autoxidation for the formation of highly oxygenated organic molecules with multiple −OOH groups, also shows a clear reduction in ROOH upon NOx addition. High-resolution mass spectrometry confirmed the production of numerous nitrogen-containing compounds. In addition, some of the compounds with low double-bond equivalents, which is likely to be correlated to ROOH formation, form in higher concentration under low NOx conditions than under high NOx conditions. In conclusion, our experimental and modeling results clearly demonstrate that NOx alters the fate and reaction pathways of peroxy radicals and hence SOA chemical composition, resulting in the reduction of ROS formation by SOA generated under high NOx conditions. The results from this study of aqueous extracts of naphthalene and α-pinene SOA provide useful insights into aqueous-phase processing of organic aerosols in the atmosphere as well as ROS formation and oxidative stress upon inhalation and respiratory deposition of SOA into lung lining fluid.

Author Information

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  • Corresponding Author
  • Authors
    • Kasey C. Edwards - Department of Chemistry, University of California, Irvine, Irvine, California 92697, United States
    • Alexandra L. Klodt - Department of Chemistry, University of California, Irvine, Irvine, California 92697, United States;  Orcidhttps://orcid.org/0000-0002-3558-972X
    • Tommaso Galeazzo - Department of Chemistry, University of California, Irvine, Irvine, California 92697, United States
    • Meredith Schervish - Department of Chemistry, University of California, Irvine, Irvine, California 92697, United States
    • Jinlai Wei - Department of Chemistry, University of California, Irvine, Irvine, California 92697, United States;  Orcidhttps://orcid.org/0000-0002-4741-9015
    • Ting Fang - Department of Chemistry, University of California, Irvine, Irvine, California 92697, United States;  Orcidhttps://orcid.org/0000-0002-4845-2749
    • Neil M. Donahue - Departments of Chemistry, Chemical Engineering, Engineering and Public Policy, Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States;  Orcidhttps://orcid.org/0000-0003-3054-2364
    • Bernard Aumont - CNRS, LISA, Univ of Paris Est Creteil and University Paris Cité, F-94010 Créteil, France
    • Sergey A. Nizkorodov - Department of Chemistry, University of California, Irvine, Irvine, California 92697, United States;  Orcidhttps://orcid.org/0000-0003-0891-0052
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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The research described in this article was conducted under contract to the Health Effects Institute (HEI) (Walter A. Rosenblith New Investigator Award 4964-RFA17-3/18-6), an organization jointly funded by the United States Environmental Protection Agency (EPA) (Assistance Award CR- 83590201) and certain motor vehicle and engine manufacturers. The contents of this article neither necessarily reflect the views of HEI, or its sponsors, nor they necessarily reflect the views and policies of the EPA or motor vehicle and engine manufacturers. The GECKO-A model is intellectual property of Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA).

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    Recent advances in our knowledge of the gas-phase oidation of isoprene, the impact of chamber walls on secondary org. aerosol (SOA) mass yields, and aerosol measurement anal. techniques warrant reevaluating SOA yields from isoprene. In particular, SOA from isoprene oidation under high-NOx conditions forms via two major pathways: (1) low-volatility nitrates and dinitrates (LV pathway) and (2) hydroymethyl-methyl-a-lactone (HMML) reaction on a surface or the condensed phase of particles to form 2-Me glyceric acid and its oligomers (2MGA pathway). These SOA prodn. pathways respond differently to reaction conditions. Past chamber expts. generated SOA with varying contributions from these two unique pathways, leading to results that are difficult to interpret. This study examines the SOA yields from these two pathways independently, which improves the interpretation of previous results and provides further understanding of the relevance of chamber SOA yields to the atm. and regional or global modeling. Results suggest that low-volatility nitrates and dinitrates produce significantly more aerosol than previously thought; the exptl. measured SOA mass yield from the LV pathway is ∼0.15. Sufficient seed surface area at the start of the reaction is needed to limit the effects of vapor wall losses of low-volatility compds. and accurately measure the complete SOA mass yield. Under dry conditions, substantial amts. of SOA are formed from HMML ring-opening reactions with inorg. ions and HMML org. oligomerization processes. However, the lactone org. oligomerization reactions are suppressed under more atmospherically relevant humidity levels, where hydration of the lactone is more competitive. This limits the SOA formation potential from the 2MGA pathway to HMML ring-opening reactions with water or inorg. ions under typical atm. conditions. The isoprene SOA mass yield from the LV pathway measured in this work is significantly higher than previous studies have reported, suggesting that low-volatility compds. such as org. nitrates and dinitrates may contribute to isoprene SOA under high-NOx conditions significantly more than previously thought and thus deserve continued study.
  14. 14
    Yan, C.; Nie, W.; Vogel, A. L.; Dada, L.; Lehtipalo, K.; Stolzenburg, D.; Wagner, R.; Rissanen, M. P.; Xiao, M.; Ahonen, L. Size-Dependent Influence of NOx on the Growth Rates of Organic Aerosol Particles. Sci. Adv. 2020, 6 (22), eaay4945,  DOI: 10.1126/sciadv.aay4945
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    Crounse, J. D.; Nielsen, L. B.; Jørgensen, S.; Kjaergaard, H. G.; Wennberg, P. O. Autoxidation of Organic Compounds in the Atmosphere. J. Phys. Chem. Lett. 2013, 4 (20), 3513– 3520,  DOI: 10.1021/jz4019207
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    Autoxidation of Organic Compounds in the Atmosphere
    Crounse, John D.; Nielsen, Lasse B.; Joergensen, Solvejg; Kjaergaard, Henrik G.; Wennberg, Paul O.
    Journal of Physical Chemistry Letters (2013), 4 (20), 3513-3520CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    A hypothesis that auto-oxidn. (inter- and intra-mol. H abstraction by peroxy radicals) plays an important role in the atm. oxidn. of org. compds., particularly org. matter assocd. with aerosols, is discussed. The rate of this process at room temp. was detd. in the lab. for a model compd., 3-pentanone. Ab-initio calcns. assessed H-shifts within a broader group of substituted org. compds. The rate of H abstraction by peroxy radicals was largely detd. by the thermochem. of nascent alkyl radicals; thus, it was highly affected by neighboring substituents. As a result, auto-oxidn. rates increased rapidly as O-contg. functional groups (carbonyl, hydroxy, hydroperoxy) are added to org. compds. This mechanism was consistent with formation of the multi-functional hydroperoxides and carbonyls often obsd. in atm. aerosol particles.
  16. 16
    Wennberg, P. O.; Bates, K. H.; Crounse, J. D.; Dodson, L. G.; McVay, R. C.; Mertens, L. A.; Nguyen, T. B.; Praske, E.; Schwantes, R. H.; Smarte, M. D. Gas-Phase Reactions of Isoprene and Its Major Oxidation Products. Chem. Rev. 2018, 118 (7), 3337– 3390,  DOI: 10.1021/acs.chemrev.7b00439
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    Gas-Phase Reactions of Isoprene and Its Major Oxidation Products
    Wennberg, Paul O.; Bates, Kelvin H.; Crounse, John D.; Dodson, Leah G.; McVay, Renee C.; Mertens, Laura A.; Nguyen, Tran B.; Praske, Eric; Schwantes, Rebecca H.; Smarte, Matthew D.; St Clair, Jason M.; Teng, Alexander P.; Zhang, Xuan; Seinfeld, John H.
    Chemical Reviews (Washington, DC, United States) (2018), 118 (7), 3337-3390CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. Isoprene carries approx. half of the flux of non-methane volatile org. carbon emitted to the atm. by the biosphere. Accurate representation of its oxidn. rate and products is essential for quantifying its influence on the abundance of the hydroxyl radical (OH), nitrogen oxide free radicals (NOx), ozone (O3), and, via the formation of highly oxygenated compds., aerosol. We present a review of recent lab. and theor. studies of the oxidn. pathways of isoprene initiated by addn. of OH, O3, the nitrate radical (NO3), and the chlorine atom. From this review, a recommendation for a nearly complete gas-phase oxidn. mechanism of isoprene and its major products is developed. The mechanism is compiled with the aims of providing an accurate representation of the flow of carbon while allowing quantification of the impact of isoprene emissions on HOx and NOx free radical concns. and of the yields of products known to be involved in condensed-phase processes. Finally, a simplified (reduced) mechanism is developed for use in chem. transport models that retains the essential chem. required to accurately simulate isoprene oxidn. under conditions where it occurs in the atm.-above forested regions remote from large NOx emissions.
  17. 17
    Bianchi, F.; Kurtén, T.; Riva, M.; Mohr, C.; Rissanen, M. P.; Roldin, P.; Berndt, T.; Crounse, J. D.; Wennberg, P. O.; Mentel, T. F. Highly Oxygenated Organic Molecules (HOM) from Gas-Phase Autoxidation Involving Peroxy Radicals: A Key Contributor to Atmospheric Aerosol. Chem. Rev. 2019, 119 (6), 3472– 3509,  DOI: 10.1021/acs.chemrev.8b00395
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    17
    Highly Oxygenated Molecules (HOM) from Gas-Phase Autoxidation Involving Organic Peroxy Radicals: A Key Contributor to Atmospheric Aerosol
    Bianchi, Federico; Kurten, Theo; Riva, Matthieu; Mohr, Claudia; Rissanen, Matti P.; Roldin, Pontus; Berndt, Torsten; Crounse, John D.; Wennberg, Paul O.; Mentel, Thomas F.; Wildt, Jurgen; Junninen, Heikki; Jokinen, Tuija; Kulmala, Markku; Worsnop, Douglas R.; Thornton, Joel A.; Donahue, Neil; Kjaergaard, Henrik G.; Ehn, Mikael
    Chemical Reviews (Washington, DC, United States) (2019), 119 (6), 3472-3509CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review which defines highly oxygenated org. mols. (HOM) formed in the atm. via auto-oxidn. involving peroxy radicals arising from volatile org. compds. describing currently available techniques for their identification/quantification, followed by a summary of the current knowledge on their formation mechanisms and physicochem. properties, is given. Major aims are to provide a common frame for the currently quite fragmented literature on HOM studies and highlighting existing gaps, and suggesting directions for future HOM research. Topics discussed include: introduction; HOM background (defining key concepts, HOM in relation to other classification schemes, historical naming conventions); HOM detection (gas and particle phases, uncertainties and anal. challenges of HOM detection); HOM formation mechanisms (auto-oxidn. involving peroxy radical as HOM source, bimol. RO2 reactions, factors affecting HOM formation); HOM properties and atm. fate (physicochem. properties, removal mechanisms); HOM atm. observations and impact (ambient HOM observation, atm. impact); and summary and perspectives.
  18. 18
    Daellenbach, K. R.; Uzu, G.; Jiang, J.; Cassagnes, L.-E.; Leni, Z.; Vlachou, A.; Stefenelli, G.; Canonaco, F.; Weber, S.; Segers, A. Sources of Particulate-Matter Air Pollution and Its Oxidative Potential in Europe. Nature 2020, 587 (7834), 414– 419,  DOI: 10.1038/s41586-020-2902-8
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    18
    Sources of particulate-matter air pollution and its oxidative potential in Europe
    Daellenbach, Kaspar R.; Uzu, Gaelle; Jiang, Jianhui; Cassagnes, Laure-Estelle; Leni, Zaira; Vlachou, Athanasia; Stefenelli, Giulia; Canonaco, Francesco; Weber, Samuel; Segers, Arjo; Kuenen, Jeroen J. P.; Schaap, Martijn; Favez, Olivier; Albinet, Alexandre; Aksoyoglu, Sebnem; Dommen, Josef; Baltensperger, Urs; Geiser, Marianne; El Haddad, Imad; Jaffrezo, Jean-Luc; Prevot, Andre S. H.
    Nature (London, United Kingdom) (2020), 587 (7834), 414-419CODEN: NATUAS; ISSN:0028-0836. (Nature Research)
    Abstr.: Particulate matter is a component of ambient air pollution that has been linked to millions of annual premature deaths globally1-3. Assessments of the chronic and acute effects of particulate matter on human health tend to be based on mass concn., with particle size and compn. also thought to play a part4. Oxidative potential has been suggested to be one of the many possible drivers of the acute health effects of particulate matter, but the link remains uncertain5-8. Studies investigating the particulate-matter components that manifest an oxidative activity have yielded conflicting results7. In consequence, there is still much to be learned about the sources of particulate matter that may control the oxidative potential concn.7. Here we use field observations and air-quality modeling to quantify the major primary and secondary sources of particulate matter and of oxidative potential in Europe. We find that secondary inorg. components, crustal material and secondary biogenic org. aerosols control the mass concn. of particulate matter. By contrast, oxidative potential concn. is assocd. mostly with anthropogenic sources, in particular with fine-mode secondary org. aerosols largely from residential biomass burning and coarse-mode metals from vehicular non-exhaust emissions. Our results suggest that mitigation strategies aimed at reducing the mass concns. of particulate matter alone may not reduce the oxidative potential concn. If the oxidative potential can be linked to major health impacts, it may be more effective to control specific sources of particulate matter rather than overall particulate mass.
  19. 19
    Xiong, Q.; Yu, H.; Wang, R.; Wei, J.; Verma, V. Rethinking Dithiothreitol-Based Particulate Matter Oxidative Potential: Measuring Dithiothreitol Consumption versus Reactive Oxygen Species Generation. Environ. Sci. Technol. 2017, 51 (11), 6507– 6514,  DOI: 10.1021/acs.est.7b01272
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    19
    Rethinking Dithiothreitol-Based Particulate Matter Oxidative Potential: Measuring Dithiothreitol Consumption versus Reactive Oxygen Species Generation
    Xiong, Qianshan; Yu, Haoran; Wang, Runran; Wei, Jinlai; Verma, Vishal
    Environmental Science & Technology (2017), 51 (11), 6507-6514CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    We measured the rate of generation of reactive oxygen species (ROS) [hydroxyl radicals (•OH) and hydrogen peroxide (H2O2)] catalyzed by ambient particulate matter (PM) in the dithiothreitol (DTT) assay. To understand the mechanism of ROS generation, we tested several redox-active substances, such as 9,10-phenanthrenequinone (PQ), 5-hydroxy-1,4-naphthoquinone (5H-1,4NQ), 1,2-naphthoquinone (1,2-NQ), 1,4-naphthoquinone (1,4-NQ), copper(II), manganese(II), and iron (II and III). Both pure compds. and their mixts. show different patterns in DTT oxidn. vs. ROS generation. The quinones, known to oxidize DTT in the efficiency order of PQ > 5H-1,4NQ > 1,2-NQ > 1,4-NQ, show a different efficiency order (5H-1,4NQ > 1,2-NQ ≈ PQ > 1,4-NQ) in the ROS generation. Cu(II), a dominant metal in DTT oxidn., contributes almost negligibly to the ROS generation. Fe is mostly inactive in DTT oxidn., but shows synergistic effect in •OH formation in the presence of other quinones (mixt./sum > 1.5). Ten ambient PM samples collected from an urban site were analyzed, and although DTT oxidn. was significantly correlated with H2O2 generation (Pearson's r = 0.91), no correlation was obsd. between DTT oxidn. and •OH formation. Our results show that measuring both DTT consumption and ROS generation in the DTT assay is important to incorporate the synergistic contribution from different aerosol components and to provide a more inclusive picture of the ROS activity of ambient PM.
  20. 20
    Fang, T.; Lakey, P. S. J.; Weber, R. J.; Shiraiwa, M. Oxidative Potential of Particulate Matter and Generation of Reactive Oxygen Species in Epithelial Lining Fluid. Environ. Sci. Technol. 2019, 53 (21), 12784– 12792,  DOI: 10.1021/acs.est.9b03823
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    20
    Oxidative Potential of Particulate Matter and Generation of Reactive Oxygen Species in Epithelial Lining Fluid
    Fang, Ting; Lakey, Pascale S. J.; Weber, Rodney J.; Shiraiwa, Manabu
    Environmental Science & Technology (2019), 53 (21), 12784-12792CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Reactive oxygen species (ROS) play a central role in adverse health effects of atm. particulate matter (PM). Respiratory deposition can lead to ROS formation in epithelial lining fluid due to redox reactions of PM components with lung antioxidants. Since direct ROS quantification is challenging, PM oxidative potential is more commonly measured using antioxidant surrogates, including dithiothreitol (DTT) and ascorbic acid, assuming that surrogate decay corresponds with ROS formation. This assumption has not been validated and the lack of ROS quantification in the respiratory tract causes major limitations in evaluating PM impacts on oxidative stress. By combining field measurements of size-segregated chem. compn., a human respiratory tract model, and kinetic modeling, the authors quantified prodn. rates and concns. of different types of ROS in different regions of the epithelial lining fluid by considering particle size-dependent respiratory deposition. The extra-thoracic region had higher ROS concns. vs. bronchial and alveolar regions. While H2O2 and O2- prodn. is governed by Fe and Cu ions, OH- are mainly generated by org. compds. and metal ions Fenton-like reactions. In winter affected by biomass burning, model comparisons suggested humic-like substances contribute substantially to ROS formation. PM oxidative potential was detd. to be a good indicator of chem. H2O2 and O2- prodn., but did not represent OH- generation. Results provided rationale and limitations for using oxidative potential as an indicator for PM toxicity in epidemiol. and toxicol. studies.
  21. 21
    Wei, J.; Fang, T.; Wong, C.; Lakey, P. S. J.; Nizkorodov, S. A.; Shiraiwa, M. Superoxide Formation from Aqueous Reactions of Biogenic Secondary Organic Aerosols. Environ. Sci. Technol. 2021, 55 (1), 260– 270,  DOI: 10.1021/acs.est.0c07789
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    21
    Superoxide formation from aqueous reactions of biogenic secondary organic aerosols
    Wei, Jinlai; Fang, Ting; Wong, Cynthia; Lakey, Pascale S. J.; Nizkorodov, Sergey A.; Shiraiwa, Manabu
    Environmental Science & Technology (2021), 55 (1), 260-270CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Reactive oxygen species (ROS) play a central role in aq.-phase processing and health effects of atm. aerosols. Although hydroxyl radical (•OH) and hydrogen peroxide (H2O2) are regarded as major oxidants assocd. with secondary org. aerosols (SOA), the kinetics and reaction mechanisms of superoxide (O2•-) formation are rarely quantified and poorly understood. Here, we demonstrate a dominant formation of O2•- with molar yields of 0.01-0.03% from aq. reactions of biogenic SOA generated by •OH photooxidn. of isoprene, β-pinene, α-terpineol, and D-limonene. The temporal evolution of •OH and O2•- formation is elucidated by kinetic modeling with a cascade of aq. reactions including the decompn. of org. hydroperoxides, •OH oxidn. of primary or secondary alcs., and unimol. decompn. of α-hydroxyperoxyl radicals. Relative yields of various types of ROS reflect a relative abundance of org. hydroperoxides and alcs. contained in SOA. These findings and mechanistic understanding have important implications on the atm. fate of SOA and particle-phase reactions of highly oxygenated org. mols. as well as oxidative stress upon respiratory deposition.
  22. 22
    Tong, H.; Arangio, A. M.; Lakey, P. S. J.; Berkemeier, T.; Liu, F.; Kampf, C. J.; Brune, W. H.; Pöschl, U.; Shiraiwa, M. Hydroxyl Radicals from Secondary Organic Aerosol Decomposition in Water. Atmospheric Chem. Phys. 2016, 16 (3), 1761– 1771,  DOI: 10.5194/acp-16-1761-2016
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    Hydroxyl radicals from secondary organic aerosol decomposition in water
    Tong, Haijie; Arangio, Andrea M.; Lakey, Pascale S. J.; Berkemeier, Thomas; Liu, Fobang; Kampf, Christopher J.; Brune, William H.; Poeschl, Ulrich; Shiraiwa, Manabu
    Atmospheric Chemistry and Physics (2016), 16 (3), 1761-1771CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
    We found that ambient and lab.-generated secondary org. aerosols (SOA) form substantial amts. of OH radicals upon interaction with liq. water, which can be explained by the decompn. of org. hydroperoxides. The molar OH yield from SOA formed by ozonolysis of terpenes (α-pinene, β-pinene, limonene) is ∼0.1% upon extn. with pure water and increases to ∼1.5% in the presence of Fe2+ ions due to Fenton-like reactions. Upon extn. of SOA samples from OH photooxidn. of isoprene, we also detected OH yields of around ∼0.1 %, which increases upon addn. of Fe2+. Our findings imply that the chem. reactivity and aging of SOA particles is strongly enhanced upon interaction with water and iron. In cloud droplets under dark conditions, SOA decompn. can compete with the classical H2O2 Fenton reaction as the source of OH radicals. Also in the human respiratory tract, the inhalation and deposition of SOA particles may lead to a substantial release of OH radicals, which may contribute to oxidative stress and play an important role in the adverse health effects of atm. aerosols.
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    Shiraiwa, M.; Selzle, K.; Pöschl, U. Hazardous Components and Health Effects of Atmospheric Aerosol Particles: Reactive Oxygen Species, Soot, Polycyclic Aromatic Compounds and Allergenic Proteins. Free Radic. Res. 2012, 46 (8), 927– 939,  DOI: 10.3109/10715762.2012.663084
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    23
    Hazardous components and health effects of atmospheric aerosol particles: reactive oxygen species, soot, polycyclic aromatic compounds and allergenic proteins
    Shiraiwa, Manabu; Selzle, Kathrin; Poeschl, Ulrich
    Free Radical Research (2012), 46 (8), 927-939CODEN: FRARER; ISSN:1029-2470. (Informa Healthcare)
    A review. This review outlines recent advances in the investigation of the chem. properties, mol. interactions and health effects of hazardous compds. in atm. aerosols, in particular reactive oxygen species (ROS), soot, polycyclic arom. compds. (PACs) and allergenic proteins. Epidemiol. studies show correlations between air particulate matter and adverse health effects of air pollution including allergy, asthma, cardiovascular and respiratory diseases, but the causative relations and mechanisms of interaction on the mol. level are still unclear. ROS generated by photochem. and heterogeneous reactions in the atm. seem to play a key role in aerosol health effects and provide a direct link between atm. and physiol. multiphase processes. Soot and PACs can trigger formation of ROS in vivo, leading to inflammation and cellular damage. PACs as well as allergenic proteins are efficiently oxygenated and nitrated upon exposure to ozone and nitrogen dioxide, which leads to an enhancement of their toxicity and allergenicity.
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    Lakey, P. S. J.; Berkemeier, T.; Tong, H.; Arangio, A. M.; Lucas, K.; Pöschl, U.; Shiraiwa, M. Chemical Exposure-Response Relationship between Air Pollutants and Reactive Oxygen Species in the Human Respiratory Tract. Sci. Rep. 2016, 6 (1), 32916,  DOI: 10.1038/srep32916
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    Chemical exposure-response relationship between air pollutants and reactive oxygen species in the human respiratory tract
    Lakey, Pascale S. J.; Berkemeier, Thomas; Tong, Haijie; Arangio, Andrea M.; Lucas, Kurt; Poeschl, Ulrich; Shiraiwa, Manabu
    Scientific Reports (2016), 6 (), 32916CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
    Air pollution can cause oxidative stress and adverse health effects such as asthma and other respiratory diseases, but the underlying chem. processes are not well characterized. Here we present chem. exposure-response relations between ambient concns. of air pollutants and the prodn. rates and concns. of reactive oxygen species (ROS) in the epithelial lining fluid (ELF) of the human respiratory tract. In highly polluted environments, fine particulate matter (PM2.5) contg. redox-active transition metals, quinones, and secondary org. aerosols can increase ROS concns. in the ELF to levels characteristic for respiratory diseases. Ambient ozone readily sats. the ELF and can enhance oxidative stress by depleting antioxidants and surfactants. Chem. exposure-response relations provide a quant. basis for assessing the relative importance of specific air pollutants in different regions of the world, showing that aerosol-induced epithelial ROS levels in polluted megacity air can be several orders of magnitude higher than in pristine rainforest air.
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    Li, N.; Xia, T.; Nel, A. E. The Role of Oxidative Stress in Ambient Particulate Matter-Induced Lung Diseases and Its Implications in the Toxicity of Engineered Nanoparticles. Free Radic. Biol. Med. 2008, 44 (9), 1689– 1699,  DOI: 10.1016/j.freeradbiomed.2008.01.028
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    25
    The role of oxidative stress in ambient particulate matter-induced lung diseases and its implications in the toxicity of engineered nanoparticles
    Li, Ning; Xia, Tian; Nel, Andre E.
    Free Radical Biology & Medicine (2008), 44 (9), 1689-1699CODEN: FRBMEH; ISSN:0891-5849. (Elsevier)
    A review. Ambient particulate matter (PM) is an environmental factor that has been assocd. with increased respiratory morbidity and mortality. The major effect of ambient PM on the pulmonary system is the exacerbation of inflammation, esp. in susceptible people. One of the mechanisms by which ambient PM exerts its proinflammatory effects is the generation of oxidative stress by its chem. compds. and metals. Cellular responses to PM-induced oxidative stress include activation of antioxidant defense, inflammation, and toxicity. The proinflammatory effect of PM in the lung is characterized by increased cytokine/chemokine prodn. and adhesion mol. expression. Moreover, there is evidence that ambient PM can act as an adjuvant for allergic sensitization, which raises the possibility that long-term PM exposure may lead to increased prevalence of asthma. In addn. to ambient PM, rapid expansion of nanotechnol. has introduced the potential that engineered nanoparticles (NP) may also become airborne and may contribute to pulmonary diseases by novel mechanisms that could include oxidant injury. Currently, little is known about the potential adverse health effects of these particles. In this communication, the mechanisms by which particulate pollutants, including ambient PM and engineered NP, exert their adverse effects through the generation of oxidative stress and the impacts of oxidant injury in the respiratory tract will be reviewed. The importance of cellular antioxidant and detoxification pathways in protecting against particle-induced lung damage will also be discussed.
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    Mazzoli-Rocha, F.; Fernandes, S.; Einicker-Lamas, M.; Zin, W. A. Roles of Oxidative Stress in Signaling and Inflammation Induced by Particulate Matter. Cell Biol. Toxicol. 2010, 26 (5), 481– 498,  DOI: 10.1007/s10565-010-9158-2
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    Roles of oxidative stress in signaling and inflammation induced by particulate matter
    Mazzoli-Rocha, Flavia; Fernandes, Silviane; Einicker-Lamas, Marcelo; Zin, Walter Araujo
    Cell Biology and Toxicology (2010), 26 (5), 481-498CODEN: CBTOE2; ISSN:0742-2091. (Springer)
    A review. This review reports the role of oxidative stress in impairing the function of lung exposed to particulate matter (PM). PM constitutes a heterogeneous mixt. of various types of particles, many of which are likely to be involved in oxidative stress induction and respiratory diseases. Probably, the ability of PM to cause oxidative stress underlies the assocn. between increased exposure to PM and exacerbations of lung disease. Mostly because of their large surface area, ultrafine particles have been shown to cause oxidative stress and proinflammatory effects in different in vivo and in vitro studies. Particle components and surface area may act synergistically inducing lung inflammation. In this vein, reactive oxygen species elicited upon PM exposure have been shown to activate a no. of redox-responsive signaling pathways and Ca2+ influx in lung target cells that are involved in the expression of genes that modulate relevant responses to lung inflammation and disease.
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    Gehling, W.; Dellinger, B. Environmentally Persistent Free Radicals and Their Lifetimes in PM2.5. Environ. Sci. Technol. 2013, 47 (15), 8172– 8178,  DOI: 10.1021/es401767m
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    Environmentally Persistent Free Radicals and Their Lifetimes in PM2.5
    Gehling, William; Dellinger, Barry
    Environmental Science & Technology (2013), 47 (15), 8172-8178CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    For the first time, an expansive study into the concn. and extended decay behavior of environmentally persistent free radicals in PM2.5 was performed. Results from this study revealed three types of radical decay-a fast decay, slow decay, and no decay-following one of four decay patterns: a relatively fast decay exhibiting a 1/e lifetime of 1-21 days accompanied by a slow decay with a 1/e lifetime of 21-5028 days (47% of samples); a single slow decay including a 1/e lifetime of 4-2083 days (24% of samples); no decay (18% of samples); and a relatively fast decay displaying an av. 1/e lifetime of 0.25-21 days followed by no decay (11% of samples). Phenol correlated well with the initial radical concn. and fast decay rate. Other correlations for common atm. pollutants (ozone, NOx, SO2, etc.) as well as meteorol. conditions suggested photochem. processes impact the initial radical concn. and fast decay rate. The radical signal in PM2.5 was remarkably similar to semiquinones in cigarette smoke. Accordingly, radicals inhaled from PM2.5 were related to the radicals inhaled from smoking cigarettes, expressed as the no. of equiv. cigarettes smoked. This calcd. to 0.4-0.9 cigarettes per day for nonextreme air quality in the United States.
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    Chowdhury, P. H.; He, Q.; Carmieli, R.; Li, C.; Rudich, Y.; Pardo, M. Connecting the Oxidative Potential of Secondary Organic Aerosols with Reactive Oxygen Species in Exposed Lung Cells. Environ. Sci. Technol. 2019, 53 (23), 13949– 13958,  DOI: 10.1021/acs.est.9b04449
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    Connecting the Oxidative Potential of Secondary Organic Aerosols with Reactive Oxygen Species in Exposed Lung Cells
    Chowdhury, Pratiti Home; He, Quanfu; Carmieli, Raanan; Li, Chunlin; Rudich, Yinon; Pardo, Michal
    Environmental Science & Technology (2019), 53 (23), 13949-13958CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    It has been hypothesized that the cytotoxicity of secondary org. aerosols (SOA) is mediated through the formation of reactive oxygen species (ROS) in the exposed cells. Here, lung epithelial cells (A549) residing at the air-liq. interface were exposed to proxies of anthropogenic and biogenic SOA that were photochem. aged under varying nitrogen oxide (NOx) concns. in an oxidn. flow reactor (OFR). The total org. peroxides and ROS radical content in the SOA were quantified by the iodometric-spectrophotometric method and by continuous-wave ESR (CW-EPR). The effect of the exposure was evaluated by measuring cell viability and cellular ROS prodn. following the exposure. The results demonstrate that SOA that aged in the absence of NOx contained more ROS than fresh SOA and were more toxic towards the cells, while varying NOx conditions had no significant influence on levels of ROS content in fresh SOA and their toxicity. Anal. of ROS in the exposed cells using flow cytometry showed a similar trend with the total ROS content in the SOA. This study provides a first and direct observation of such assocn.
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    Tong, H.; Lakey, P. S. J.; Arangio, A. M.; Socorro, J.; Shen, F.; Lucas, K.; Brune, W. H.; Pöschl, U.; Shiraiwa, M. Reactive Oxygen Species Formed by Secondary Organic Aerosols in Water and Surrogate Lung Fluid. Environ. Sci. Technol. 2018, 52 (20), 11642– 11651,  DOI: 10.1021/acs.est.8b03695
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    29
    Reactive Oxygen Species Formed by Secondary Organic Aerosols in Water and Surrogate Lung Fluid
    Tong, Haijie; Lakey, Pascale S. J.; Arangio, Andrea M.; Socorro, Joanna; Shen, Fangxia; Lucas, Kurt; Brune, William H.; Poeschl, Ulrich; Shiraiwa, Manabu
    Environmental Science & Technology (2018), 52 (20), 11642-11651CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Reactive O species (ROS) play a central role in the adverse health effects of air pollutants. Respiratory deposition of fine air particulate matter can lead to ROS formation in epithelial lining fluid, potentially causing oxidative stress and inflammation. Secondary org. aerosols (SOA) account for a large fraction of fine particulate matter, but their role in adverse health effects is unclear. This work quantified and compared ROS yields and oxidative potential of isoprene, β-pinene, and naphthalene SOA in water and surrogate lung fluid (SLF). In pure water, isoprene and β-pinene SOA produced mainly OH- and org. radicals; naphthalene SOA produced mainly H2O2 and O2-. Total molar ROS yields of isoprene and β-pinene SOA were 11.8 and 8.2% in water and decreased to 8.5 and 5.2% in SLF, resp., attributed to ROS removal by lung antioxidants. A pos. correlation between total peroxide concn. and ROS yield suggested org. (hydro)peroxides may play an important role in ROS formation from biogenic SOA. Total molar ROS yield of naphthalene SOA was 1.7% in water and increased to 11.3% in SLF. This strong increase was likely due to redox reaction cycles involving environmentally persistent free radicals or semiquinones, antioxidants, and O2, which may promote H2O2 formation and adverse health effects of anthropogenic SOA from arom. precursors.
  30. 30
    Vejerano, E. P.; Rao, G.; Khachatryan, L.; Cormier, S. A.; Lomnicki, S. Environmentally Persistent Free Radicals: Insights on a New Class of Pollutants. Environ. Sci. Technol. 2018, 52 (5), 2468– 2481,  DOI: 10.1021/acs.est.7b04439
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    Environmentally Persistent Free Radicals: Insights on a New Class of Pollutants
    Vejerano, Eric P.; Rao, Guiying; Khachatryan, Lavrent; Cormier, Stephania A.; Lomnicki, Slawo
    Environmental Science & Technology (2018), 52 (5), 2468-2481CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Environmentally persistent free radicals, EPFRs, exist in significant concn. in atm. particulate matter (PM). EPFRs are primarily emitted from combustion and thermal processing of org. materials, in which the org. combustion byproducts interact with transition metal-contg. particles to form a free radical-particle pollutant. While the existence of persistent free radicals in combustion has been known for over half-a-century, only recently that their presence in environmental matrixes and health effects have started significant research, but still in its infancy. Most of the exptl. studies conducted to understand the origin and nature of EPFRs have focused primarily on nanoparticles that are supported on a larger micrometer-sized particle that mimics incidental nanoparticles formed during combustion. Less is known on the extent by which EPFRs may form on engineered nanomaterials (ENMs) during combustion or thermal treatment. In this crit. and timely review, we summarize important findings on EPFRs and discuss their potential to form on pristine ENMs as a new research direction. ENMs may form EPFRs that may differ in type and concn. compared to nanoparticles that are supported on larger particles. The lack of basic data and fundamental knowledge about the interaction of combustion byproducts with ENMs under high-temp. and oxidative conditions present an unknown environmental and health burden. Studying the extent of ENMs on catalyzing EPFRs is important to address the hazards of atm. PM fully from these emerging environmental contaminants.
  31. 31
    Gehling, W.; Khachatryan, L.; Dellinger, B. Hydroxyl Radical Generation from Environmentally Persistent Free Radicals (EPFRs) in PM2.5. Environ. Sci. Technol. 2014, 48 (8), 4266– 4272,  DOI: 10.1021/es401770y
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    Hydroxyl Radical Generation from Environmentally Persistent Free Radicals (EPFRs) in PM2.5
    Gehling, William; Khachatryan, Lavrent; Dellinger, Barry
    Environmental Science & Technology (2014), 48 (8), 4266-4272CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Hydroxyl radicals generated from an aq. suspension of ambient PM2.5 and detected using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) in a spin trap in conjunction with ESR spectroscopy is discussed. Study results suggested the importance of environmentally persistent free radicals (EPFR) in PM2.5 to generate significant OH- concns. without adding H2O2. Particles for which EPFR were allowed to decay over time induced less OH-; also, higher particle concns. produced more OH-. Some samples did not alter OH- generation when the soln. was purged with air. This was ascribed to internal vs. external surface-assocd. EPFR.
  32. 32
    Kumagai, Y.; Koide, S.; Taguchi, K.; Endo, A.; Nakai, Y.; Yoshikawa, T.; Shimojo, N. Oxidation of Proximal Protein Sulfhydryls by Phenanthraquinone, a Component of Diesel Exhaust Particles. Chem. Res. Toxicol. 2002, 15 (4), 483– 489,  DOI: 10.1021/tx0100993
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    Oxidation of Proximal Protein Sulfhydryls by Phenanthraquinone, a Component of Diesel Exhaust Particles
    Kumagai, Yoshito; Koide, Sachie; Taguchi, Keiko; Endo, Akiko; Nakai, Yumi; Yoshikawa, Toshikazu; Shimojo, Nobuhiro
    Chemical Research in Toxicology (2002), 15 (4), 483-489CODEN: CRTOEC; ISSN:0893-228X. (American Chemical Society)
    Diesel exhaust particles (DEP) contain quinones that are capable of catalyzing the generation of reactive oxygen species in biol. systems, resulting in induction of oxidative stress. In the present study, we explored sulfhydryl oxidn. by phenanthraquinone, a component of DEP, using thiol compds. and protein prepns. Phenanthraquinone reacted readily with dithiol compds. such as dithiothreitol (DTT), 2,3-dimercapto-1-propanol (BAL), and 2,3-dimercapto-1-propanesulfonic acid (DMPS), resulting in modification of the thiol groups, whereas minimal reactivities of this quinone with monothiol compds. such as GSH, 2-mercaptoethanol, and N-acetyl-L-cysteine were seen. The modification of DTT dithiol caused by phenanthraquinone proceeded under anaerobic conditions but was accelerated by mol. oxygen. Phenanthraquinone was also capable of modifying thiol groups in pulmonary microsomes from rats and total membrane prepn. isolated from bovine aortic endothelial cells (BAEC), but not bovine serum albumin (BSA), which has a Cys34 as a reactive monothiol group. A comparison of the thiol alkylating agent N-ethylmaleimide (NEM) with that of phenanthraquinone indicates that the two mechanisms of thiol modification are distinct. Studies revealed that thiyl radical intermediates and reactive oxygen species were generated during interaction of phenanthraquinone with DTT. From these findings, it is suggested that phenanthraquinone-mediated destruction of protein sulfhydryls appears to involve the oxidn. of presumably proximal thiols and the redn. of mol. oxygen.
  33. 33
    Arangio, A. M.; Tong, H.; Socorro, J.; Pöschl, U.; Shiraiwa, M. Quantification of Environmentally Persistent Free Radicals and Reactiveoxygen Species in Atmospheric Aerosol Particles. Atmospheric Chem. Phys. 2016, 16 (20), 13105– 13119,  DOI: 10.5194/acp-16-13105-2016
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    Quantification of environmentally persistent free radicals and reactive oxygen species in atmospheric aerosol particles
    Arangio, Andrea M.; Tong, Haijie; Socorro, Joanna; Poeschl, Ulrich; Shiraiwa, Manabu
    Atmospheric Chemistry and Physics (2016), 16 (20), 13105-13119CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
    Fine particulate matter plays a central role in the adverse health effects of air pollution. Inhalation and deposition of aerosol particles in the respiratory tract can lead to the release of reactive oxygen species (ROS), which may cause oxidative stress. In this study, we have detected and quantified a wide range of particle-assocd. radicals using ESR (EPR) spectroscopy. Ambient particle samples were collected using a cascade impactor at a semi-urban site in central Europe, Mainz, Germany, in May-June 2015. Concns. of environmentally persistent free radicals (EPFR), most likely semiquinone radicals, were found to be in the range of (1-7) × 1011 spins μg-1 for particles in the accumulation mode, whereas coarse particles with a diam. larger than 1 μm did not contain substantial amts. of EPFR. Using a spin trapping technique followed by deconvolution of EPR spectra, we have also characterized and quantified ROS, including OH, superoxide (O-2) and formed upon extn. of the particle samples in water. Total ROS amts. of (0.1-3) × 1011 spins μg-1 were released by submicron particle samples and the relative contributions of OH, O-2, C-centered and O-centered org. radicals were ∼11-31, ∼2-8, ∼41-72 and ∼0-25 %, resp., depending on particle sizes. OH was the dominant species for coarse particles. Based on comparisons of the EPR spectra of ambient particulate matter with those of mixts. of org. hydroperoxides, quinones and iron ions followed by chem. anal. using liq. chromatog. mass spectrometry (LC-MS), we suggest that the particle-assocd. ROS were formed by decompn. of org. hydroperoxides interacting with transition metal ions and quinones contained in atm. humic-like substances.
  34. 34
    Chen, Q.; Wang, M.; Wang, Y.; Zhang, L.; Xue, J.; Sun, H.; Mu, Z. Rapid Determination of Environmentally Persistent Free Radicals (EPFRs) in Atmospheric Particles with a Quartz Sheet-Based Approach Using Electron Paramagnetic Resonance (EPR) Spectroscopy. Atmos. Environ. 2018, 184, 140– 145,  DOI: 10.1016/j.atmosenv.2018.04.046
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    Rapid determination of environmentally persistent free radicals (EPFRs) in atmospheric particles with a quartz sheet-based approach using electron paramagnetic resonance (EPR) spectroscopy
    Chen, Qingcai; Wang, Mamin; Wang, Yuqin; Zhang, Lixin; Xue, Jian; Sun, Haoyao; Mu, Zhen
    Atmospheric Environment (2018), 184 (), 140-145CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
    Environmentally persistent free radicals (EPFRs) are present within atm. fine particles, and they are assumed to be a potential factor responsible for human pneumonia and lung cancer. This study presents a new method for the rapid quantification of EPFRs in atm. particles with a quartz sheet-based approach using ESR (EPR) spectroscopy. The three-dimensional distributions of the relative response factors in a cavity resonator were simulated and utilized for an accurate quant. detn. of EPFRs in samples. Comparisons between the proposed method and conventional quant. methods were also performed to illustrate the advantages of the proposed method. The results suggest that the reproducibility and accuracy of the proposed method are superior to those of the quartz tube-based method. Although the solvent extn. method is capable of extg. specific EPFR species, the developed method can be used to det. the total EPFR content; moreover, the anal. process of the proposed approach is substantially quicker than that of the solvent extn. method. The proposed method has been applied in this study to det. the EPFRs in ambient PM2.5 samples collected over Xi'an, the results of which will be useful for extensive research on the sources, concns., and phys.-chem. characteristics of EPFRs in the atm.
  35. 35
    Borrowman, C. K.; Zhou, S.; Burrow, T. E.; Abbatt, J. P. D. Formation of Environmentally Persistent Free Radicals from the Heterogeneous Reaction of Ozone and Polycyclic Aromatic Compounds. Phys. Chem. Chem. Phys. 2016, 18 (1), 205– 212,  DOI: 10.1039/C5CP05606C
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    Formation of environmentally persistent free radicals from the heterogeneous reaction of ozone and polycyclic aromatic compounds
    Borrowman, Cuyler K.; Zhou, Shouming; Burrow, Timothy E.; Abbatt, Jonathan P. D.
    Physical Chemistry Chemical Physics (2016), 18 (1), 205-212CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    In the 1980s long-lived radical species were identified in cigarette tar. Since then, environmentally persistent free radicals (EPFR) have been obsd. in ambient particulate matter, and have been generated by an entrained in internal combustion engine particulate matter. For the first time, EPFR in-situ formation and decay was measured by the heterogeneous reaction of O3 with several polycyclic arom. compds. (PAH). Solid anthracene, pyrene, 1,4-naphthoquinone, and 9,10-anthraquinone (AQ) were reacted with gaseous O3 in a flow system installed in the active cavity of an ESR spectrometer, and radical formation was measured on a tens-of-minutes time-scale at ambient O3 concns. down to 30 ppb. For most substrates, net radical prodn. was initially rapid, slowed at intermediate times, and was followed by a slow decay. For oxidized, solid BAP, the radical signal persisted for many days in the absence of O3. To evaluate the effect of substrate phase, solid PAH were also dissolved in squalane, an org. oil inert to O3, which yielded a much higher max. radical concn. and faster radical decay when exposed to O3. With higher mobility, reactants were apparently able to more easily diffuse and react, yielding higher radical concns. EPR spectra exhibited 3 radicals types, 2 of which were assigned to semiquinone species and 1 to a PAH-derived, C-centered radical. Although the system used PAH concns. not typically obsd. in the environment, the amts. of radicals formed (on the order of 1018 radicals/g), was comparable to that obsd. in ambient particulate matter.
  36. 36
    Villamena, F. A.; Zweier, J. L. Detection of Reactive Oxygen and Nitrogen Species by EPR Spin Trapping. Antioxid. Redox Signal. 2004, 6 (3), 619– 629,  DOI: 10.1089/152308604773934387
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    Detection of reactive oxygen and nitrogen species by EPR spin trapping
    Villamena Frederick A; Zweier Jay L
    Antioxidants & redox signaling (2004), 6 (3), 619-29 ISSN:1523-0864.
    Electron paramagnetic resonance spin trapping has become an indispensable tool for the specific detection of reactive oxygen free radicals in biological systems. In this review we describe some of the advantages as well as some experimental considerations of this technique and how it can be applied to biological systems to measure oxidative stress.
  37. 37
    Klodt, A. L. ICARUS Experiment Set: APIN and NAP SOA generation for reactive oxygen species measurements, ICARUS [data set], available at: https://icarus.ucdavis.edu/experimentset/249 (accessed 2022-06-22).
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    Hinks, M. L.; Montoya-Aguilera, J.; Ellison, L.; Lin, P.; Laskin, A.; Laskin, J.; Shiraiwa, M.; Dabdub, D.; Nizkorodov, S. A. Effect of Relative Humidity on the Composition of Secondary Organic Aerosol from the Oxidation of Toluene. Atmospheric Chem. Phys. 2018, 18 (3), 1643– 1652,  DOI: 10.5194/acp-18-1643-2018
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    Effect of relative humidity on the composition of secondary organic aerosol from the oxidation of toluene
    Hinks, Mallory L.; Montoya-Aguilera, Julia; Ellison, Lucas; Lin, Peng; Laskin, Alexander; Laskin, Julia; Shiraiwa, Manabu; Dabdub, Donald; Nizkorodov, Sergey A.
    Atmospheric Chemistry and Physics (2018), 18 (3), 1643-1652CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
    The effect of relative humidity (RH) on the chem. compn. of secondary org. aerosol (SOA) formed from low-NOx toluene oxidn. in the absence of seed particles was investigated. SOA samples were prepd. in an aerosol smog chamber at < 2% RH and 75% RH, collected on Teflon filters, and analyzed with nanospray desorption electrospray ionization high-resoln. mass spectrometry (nano-DESI-HRMS). Measurements revealed a significant redn. in the fraction of oligomers present in the SOA generated at 75% RH compared to SOA generated under dry conditions. In a sep. set of expts., the particle mass concns. were measured with a scanning mobility particle sizer (SMPS) at RHs ranging from < 2 to 90%. It was found that the particle mass loading decreased by nearly an order of magnitude when RH increased from < 2 to 75-90% for low-NOx toluene SOA. The volatility distributions of the SOA compds., estd. from the distribution of mol. formulas using the "mol. corridor" approach, confirmed that low-NOx toluene SOA became more volatile on av. under high-RH conditions. In contrast, the effect of RH on SOA mass loading was found to be much smaller for high-NOx toluene SOA. The obsd. increase in the oligomer fraction and particle mass loading under dry conditions were attributed to the enhancement of condensation reactions, which produce water and oligomers from smaller compds. in low-NOx toluene SOA. The redn. in the fraction of oligomeric compds. under humid conditions is predicted to partly counteract the previously obsd. enhancement in the toluene SOA yield driven by the aerosol liq. water chem. in deliquesced inorg. seed particles.
  39. 39
    Saleh, R.; Donahue, N. M.; Robinson, A. L. Time Scales for Gas-Particle Partitioning Equilibration of Secondary Organic Aerosol Formed from Alpha-Pinene Ozonolysis. Environ. Sci. Technol. 2013, 47 (11), 5588– 5594,  DOI: 10.1021/es400078d
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    Time Scales for Gas-Particle Partitioning Equilibration of Secondary Organic Aerosol Formed from Alpha-Pinene Ozonolysis
    Saleh, Rawad; Donahue, Neil M.; Robinson, Allen L.
    Environmental Science & Technology (2013), 47 (11), 5588-5594CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Most chem. transport models assume instantaneous equil. to represent gas-particle partitioning of semivolatile org. aerosol. This approach has been challenged by recent studies suggesting that secondary org. aerosol (SOA) cannot reach equil. within atm. time scales. The emergent hypothesis is that gas-particle partitioning rates are limited by diffusion within the condensed phase, which probably is glassy. Here, we study the equilibration time scales of SOA formed from α-pinene ozonolysis by measuring the dynamic response to a modest step-change in temp. Upon heating, equil. is disturbed, and the particles evap. to restore equil. at the new temp., which is attained when evapn. ceases. The SOA was formed at 10° and then heated to near room temp. (30°) so that the phase state (viscosity) of the condensed-phase after heating is similar to how it would be in the atm. Expts. were performed in both a thermodenuder, with SOA loading of 350 μg/m3, and in a smog chamber, with SOA loading of 2-12 μg/m3. Both expts. show, contrary to previous findings, that the SOA achieves equil. with dynamic responses consistent with a mass accommodation coeff. of order 0.1. For typical atm. conditions, this translates into equilibration time scales on the order of min to tens of min, supporting the use of equil. partitioning in chem. transport models.
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    Wei, J.; Fang, T.; Lakey, P. S. J.; Shiraiwa, M. Iron-Facilitated Organic Radical Formation from Secondary Organic Aerosols in Surrogate Lung Fluid. Environ. Sci. Technol. 2022, 56 (11), 7234– 7243,  DOI: 10.1021/acs.est.1c04334
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    Iron-Facilitated Organic Radical Formation from Secondary Organic Aerosols in Surrogate Lung Fluid
    Wei, Jinlai; Fang, Ting; Lakey, Pascale S. J.; Shiraiwa, Manabu
    Environmental Science & Technology (2022), 56 (11), 7234-7243CODEN: ESTHAG; ISSN:1520-5851. (American Chemical Society)
    Respiratory deposition of secondary org. aerosols (SOA) and iron may lead to the generation of reactive oxygen species and free radicals in lung fluid to cause oxidative stress, but their underlying mechanism and formation kinetics are not well understood. Here we demonstrate substantial formation of org. radicals in surrogate lung fluid (SLF) by mixts. of Fe2+ and SOA generated from photooxidn. of isoprene, α-terpineol, and toluene. The molar yields of org. radicals by SOA are measured to be 0.03-0.5% in SLF, which are 5-10 times higher than in water. We observe that Fe2+ enhances org. radical yields dramatically by a factor of 20-80, which can be attributed to Fe2+-facilitated decompn. of org. peroxides, in consistency with a pos. correlation between peroxide contents and org. radical yields. Ascorbate mediates redox cycling of iron ions to sustain org. peroxide decompn., as supported by kinetic modeling reproducing time- and concn.-dependence of org. radical formation as well as addnl. expts. observing the formation of Fe2+ and ascorbate radicals in mixts. of ascorbate and Fe3+. •OH and superoxide are found to be scavenged by antioxidants efficiently. These findings have implications on the role of org. radicals in oxidative damage and lipid peroxidn.
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    Docherty, K. S.; Wu, W.; Lim, Y. B.; Ziemann, P. J. Contributions of Organic Peroxides to Secondary Aerosol Formed from Reactions of Monoterpenes with O3. Environ. Sci. Technol. 2005, 39 (11), 4049– 4059,  DOI: 10.1021/es050228s
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    Contributions of Organic Peroxides to Secondary Aerosol Formed from Reactions of Monoterpenes with O3
    Docherty, Kenneth S.; Wu, Wilbur; Lim, Yong Bin; Ziemann, Paul J.
    Environmental Science and Technology (2005), 39 (11), 4049-4059CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    The role of org. peroxides in secondary org. aerosol (SOA) formation from reactions of monoterpenes with O3 was investigated in a series of environmental chamber expts. Reactions were performed with endocyclic (α-pinene and Δ3-carene) and exocyclic (β-pinene and sabinene) alkenes in dry and humid air and in the presence of the OH radical scavengers: cyclohexane, 1-propanol, and formaldehyde. A thermal desorption particle beam mass spectrometer was used to probe the identity and volatility of SOA components, and an iodometric-spectrophotometric method was used to quantify org. peroxides. Thermal desorption profiles and mass spectra showed that the most volatile SOA components had vapor pressures similar to pinic acid and that much of the SOA consisted of less volatile species that were probably oligomeric compds. Peroxide analyses indicated that the SOA was predominantly org. peroxides, providing evidence that the oligomers were mostly peroxyhemiacetals formed by heterogeneous reactions of hydroperoxides and aldehydes. For example, it was estd. that org. peroxides contributed ∼47 and ∼85% of the SOA mass formed in the α- and β-pinene reactions, resp. Reactions performed with different OH radical scavengers indicated that most of the hydroperoxides were formed through the hydroperoxide channel rather than by reactions of stabilized Criegee intermediates. The effect of the OH radical scavenger on the SOA yield was also investigated, and the results were consistent with results of recent expts. and model simulations that support a mechanism based on changes in the [HO2]/[RO2] ratios. These are the first measurements of org. peroxides in monoterpene SOA, and the results have important implications for understanding the mechanisms of SOA formation and the potential effects of atm. aerosol particles on the environment and human health.
  42. 42
    Fang, T.; Verma, V.; Guo, H.; King, L. E.; Edgerton, E. S.; Weber, R. J. A Semi-Automated System for Quantifying the Oxidative Potential of Ambient Particles in Aqueous Extracts Using the Dithiothreitol (DTT) Assay: Results from the Southeastern Center for Air Pollution and Epidemiology (SCAPE). Atmospheric Meas. Technol. 2015, 8 (1), 471– 482,  DOI: 10.5194/amt-8-471-2015
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    A semi-automated system for quantifying the oxidative potential of ambient particles in aqueous extracts using the dithiothreitol (DTT) assay: results from the Southeastern Center for Air Pollution and Epidemiology (SCAPE)
    Fang, T.; Verma, V.; Guo, H.; King, L. E.; Edgerton, E. S.; Weber, R. J.
    Atmospheric Measurement Techniques (2015), 8 (1), 471-482CODEN: AMTTC2; ISSN:1867-8548. (Copernicus Publications)
    A variety of methods are used to measure the capability of particulate matter (PM) to catalytically generate reactive oxygen species (ROS) in vivo, also defined as the aerosol oxidative potential. A widely used measure of aerosol oxidative potential is the dithiothreitol (DTT) assay, which monitors the depletion of DTT (a surrogate for cellular antioxidants) as catalyzed by the redox-active species in PM. However, a major constraint in the routine use of the DTT assay for integrating it with large-scale health studies is its labor-intensive and time-consuming protocol. To specifically address this concern, we have developed a semi-automated system for quantifying the oxidative potential of aerosol liq. exts. using the DTT assay. The system, capable of unattended anal. at one sample per h, has a high anal. precision (coeff. of variation of 15% for pos. control, 4% for ambient samples) and reasonably low limit of detection (0.31 nmol min-1). Comparison of the automated approach with the manual method conducted on ambient samples yielded good agreement (slope = 1.08 ± 0.12, r2 = 0.92, N = 9). The system was utilized for the Southeastern Center for Air Pollution & Epidemiol. (SCAPE) to generate an extensive data set on DTT activity of ambient particles collected from contrasting environments (urban, roadside, and rural) in the southeastern US. We find that water-sol. PM2.5 DTT activity on a per-air-vol. basis was spatially uniform and often well correlated with PM2.5 mass (r = 0.49 to 0.88), suggesting regional sources contributing to the PM oxidative potential in the southeastern US. The correlation may also suggest a mechanistic explanation (oxidative stress) for obsd. PM2.5 mass-health assocns. The heterogeneity in the intrinsic DTT activity (per-PM-mass basis) across seasons indicates variability in the DTT activity assocd. with aerosols from sources that vary with season. Although developed for the DTT assay, the instrument can also be used to det. oxidative potential with other acellular assays.
  43. 43
    Chin, H.; Hopstock, K. S.; Fleming, L. T.; Nizkorodov, S. A.; Al-Abadleh, H. A. Effect of Aromatic Ring Substituents on the Ability of Catechol to Produce Brown Carbon in Iron(III)-Catalyzed Reactions. Environ. Sci. Atmospheres 2021, 1 (2), 64– 78,  DOI: 10.1039/D0EA00007H
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    Effect of aromatic ring substituents on the ability of catechol to produce brown carbon in iron(III)-catalyzed reactions
    Chin, Henry; Hopstock, Katherine S.; Fleming, Lauren T.; Nizkorodov, Sergey A.; Al-Abadleh, Hind A.
    Environmental Science: Atmospheres (2021), 1 (2), 64-78CODEN: ESANC9; ISSN:2634-3606. (Royal Society of Chemistry)
    Our previous work demonstrated formation of highly insol. and strongly light-absorbing org. particles in reactions between catechol or guaiacol with Fe(III) under pH = 3 conditions characteristic of aerosol liq. water. This work extends these measurements to reactions of Fe(III) with 2,4-dinitrophenol, 4-nitrocatechol, 4-methylcatechol, 1,2,4-benzenetriol, 1,2,3-benzenetriol (pyrogallol) and coniferaldehyde to better understand the mechanism of particle formation catalyzed by Fe(III). Particles were obsd. after 2 h of reactions of catechol (43 ± 1% mass yield), 1,2,4-benzenetriol (32 ± 3%), pyrogallol (27 ± 2%) and coniferaldehyde (35 ± 4%), while reactions of 2,4-dinitrophenol and 4-nitrocatechol did not produce any insol. products. No particles were obsd. in reaction of 4-methylcatechol after 2 h, however, insol. products appeared after a 24 h reaction time. Irradn. of a catechol + Fe(III) mixt. by 405 nm light was found to reduce (but not fully suppress) the particle yield due to a competition between photodegrdn. and Fe(III)-catalyzed oligomerization. Particles produced from precursors + Fe(III) solns. were dissolved in org. solvents and analyzed with ultra performance liq. chromatog. coupled to a photodiode array spectrophotometer and a high resoln. mass spectrometer. Major sepd. chromophores were identified as dimeric, trimeric, and tetrameric products of precursor mols. Purpurogallin was identified as a major reaction product of pyrogallol reaction with Fe(III). To test whether this chem. can occur in more realistic atm. aerosols, reactions of biomass burning org. aerosol (BBOA) exts. with Fe(III) were also examd. Two BBOA samples collected under flaming conditions produced no particles, whereas a BBOA sample produced under smoldering conditions resulted in particle formation under both dark and 405 nm irradn. conditions. The results suggest that Fe(III)-catalyzed chem. can take place in aging BBOA plumes resulting from smoldering fires and make aerosol particles more light-absorbing.
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    Camredon, M.; Aumont, B.; Lee-Taylor, J.; Madronich, S. The SOA/VOC/NOx System: An Explicit Model of Secondary Organic Aerosol Formation. Atmospheric Chem. Phys. 2007, 7 (21), 5599– 5610,  DOI: 10.5194/acp-7-5599-2007
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    The SOA/VOC/NOx system: an explicit model of secondary organic aerosol formation
    Camredon, M.; Aumont, B.; Lee-Taylor, J.; Madronich, S.
    Atmospheric Chemistry and Physics (2007), 7 (21), 5599-5610CODEN: ACPTCE; ISSN:1680-7316. (Copernicus Publications)
    Our current understanding of secondary org. aerosol (SOA) formation is limited by our knowledge of gaseous secondary orgs. involved in gas/particle partitioning. The objective of this study is to explore (i) the potential for products of multiple oxidn. steps contributing to SOA, and (ii) the evolution of the SOA/VOC/NOx system. We developed an explicit model based on the coupling of detailed gas-phase oxidn. schemes with a thermodn. condensation module. Such a model allows prediction of SOA mass and speciation on the basis of first principles. The SOA/VOC/NOx system is studied for the oxidn. of 1-octene under atmospherically relevant concns. In this study, gaseous oxidn. of octene is simulated to lead to SOA formation. Contributors to SOA formation are shown to be formed via multiple oxidn. steps of the parent hydrocarbon. The behavior of the SOA/VOC/NOx system simulated using the explicit model agrees with general tendencies obsd. during lab. chamber expts. This explicit modeling of SOA formation appears as a useful exploratory tool to (i) support interpretations of SOA formation obsd. in lab. chamber expts., (ii) give some insights on SOA formation under atmospherically relevant conditions and (iii) investigate implications for the regional/global lifetimes of the SOA.
  45. 45
    Aumont, B.; Szopa, S.; Madronich, S. Modelling the Evolution of Organic Carbon during Its Gas-Phase Tropospheric Oxidation: Development of an Explicit Model Based on a Self Generating Approach. Atmospheric Chem. Phys. 2005, 5 (9), 2497– 2517,  DOI: 10.5194/acp-5-2497-2005
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    45
    Modelling the evolution of organic carbon during its gas-phase tropospheric oxidation: Development of an explicit model based on a self generating approach
    Aumont, B.; Szopa, S.; Madronich, S.
    Atmospheric Chemistry and Physics (2005), 5 (9), 2497-2517CODEN: ACPTCE; ISSN:1680-7316. (European Geosciences Union)
    Org. compds. emitted in the atm. are oxidized in complex reaction sequences that produce a myriad of intermediates. Although the cumulative importance of these org. intermediates is widely acknowledged, there is still a crit. lack of information concerning the detailed compn. of the highly functionalized secondary orgs. in the gas and condensed phases. The evaluation of their impacts on pollution episodes, climate, and the tropospheric oxidizing capacity requires modeling tools that track the identity and reactivity of org. carbon in the various phases down to the ultimate oxidn. products, CO and CO2. However, a fully detailed representation of the atm. transformations of org. compds. involves a very large no. of intermediate species, far in excess of the no. that can be reasonably written manually. This paper describes (1) the development of a data processing tool to generate the explicit gas-phase oxidn. schemes of acyclic hydrocarbons and their oxidn. products under tropospheric conditions and (2) the protocol used to select the reaction products and the rate consts. Results are presented using the fully explicit oxidn. schemes generated for two test species: n-heptane and isoprene. Comparisons with well-established mechanisms were performed to evaluate these generated schemes. Some preliminary results describing the gradual change of org. carbon during the oxidn. of a given parent compd. are presented.
  46. 46
    Nannoolal, Y.; Rarey, J.; Ramjugernath, D. Estimation of Pure Component Properties. Fluid Phase Equilib. 2008, 269 (1-2), 117– 133,  DOI: 10.1016/j.fluid.2008.04.020
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    Estimation of pure component properties. Part 3. Estimation of the vapor pressure of non-electrolyte organic compounds via group contributions and group interaction
    Nannoolal, Yash; Rarey, Jurgen; Ramjugernath, Deresh
    Fluid Phase Equilibria (2008), 269 (1-2), 117-133CODEN: FPEQDT; ISSN:0378-3812. (Elsevier B.V.)
    A group contribution method for the estn. of the normal b.p. of nonelectrolyte org. compds., which was published earlier, has been the basis for development of subsequent phys. property methods. In this work, the model was extended to enable the prediction of vapor pressure data with special attention to the low-pressure region. The mol. structure of the compd. and a ref. point, usually the normal b.p., are the only required inputs and enables the estn. of vapor pressure at other temps. by group contribution. The structural group definitions are similar to those proposed earlier for the normal b.p., with minor modifications having been made to improve the predictions. Structural groups were defined in a standardized form and fragmentation of the mol. structures was performed by an automatic procedure to eliminate any arbitrary assumptions. The new method is based on vapor pressure data for more than 1600 components. The results of the new method are compared to the Antoine correlative equation using parameters stored in the Dortmund Data Bank, as well as, the DIPPR vapor pressure correlations. The group contribution method has proven to be a good predictor, with accuracies comparable to the correlations. Moreover, because the regression of group contributions was performed for a large no. of compds., the results can in several cases be considered more reliable than those of the correlative models that were regressed to individual components only. The range of the method is usually from about the triple or m.p. to a reduced temp. of 0.75-0.8.
  47. 47
    Vereecken, L.; Peeters, J. Decomposition of Substituted Alkoxy Radicals─Part I: A Generalized Structure–Activity Relationship for Reaction Barrier Heights. Phys. Chem. Chem. Phys. 2009, 11 (40), 9062– 9074,  DOI: 10.1039/b909712k
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    Decomposition of substituted alkoxy radicals-part I: a generalized structure-activity relationship for reaction barrier heights
    Vereecken, L.; Peeters, J.
    Physical Chemistry Chemical Physics (2009), 11 (40), 9062-9074CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    An update and expansion of our readily applicable structure-activity relationship (SAR) for predicting the barrier height Eb to decompn. by β C-C scission of (substituted) alkoxy radicals is presented. Such alkoxy radicals are key intermediates in the atm. oxidn. of volatile org. compds., and a correct description of their chem. is vital to the understanding of atm. chem.; nevertheless, exptl. data on these reactions remain scarce. The SAR is based on quantum chem. characterizations of a large set of alkoxy radicals, and accommodates alkoxy radicals with alkyl- (-R), oxo- (=O), hydroxy- (-OH), hydroperoxy (-OOH), alkoxy (-OR), alkylperoxy- (-OOR), nitroso- (-NO), nitro- (-NO2), nitrosooxy- (-ONO), and nitroxy- (-ONO2) functionalities, as well as 3- to 6-membered rings and some unsatd. side chains. The SAR expresses the barrier height to decompn., Eb = 17.9 kcal mol-1 + ΣNs×Fs, as a linear function of the no. Ns of these substituents on the relevant carbons, and the substituent-specific activities Fs derived from the quantum chem. calcns., allowing facile predictions based solely on the mol. structure. For low barriers, ≤7 kcal mol-1, a simple curvature correction is required. The SAR-predicted barrier height Eb can be used to predict the high-pressure rate coeff. for alkoxy decompn. kdiss at or around 298 K.
  48. 48
    Jenkin, M. E.; Valorso, R.; Aumont, B.; Rickard, A. R. Estimation of Rate Coefficients and Branching Ratios for Reactions of Organic Peroxy Radicals for Use in Automated Mechanism Construction. Atmospheric Chem. Phys. 2019, 19 (11), 7691– 7717,  DOI: 10.5194/acp-19-7691-2019
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    Estimation of rate coefficients and branching ratios for reactions of organic peroxy radicals for use in automated mechanism construction
    Jenkin, Michael E.; Valorso, Richard; Aumont, Bernard; Rickard, Andrew R.
    Atmospheric Chemistry and Physics (2019), 19 (11), 7691-7717CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
    Org. peroxy radicals (RO2), formed from the degrdn. of hydrocarbons and other volatile org. compds. (VOCs), play a key role in tropospheric oxidn. mechanisms. Several competing reactions may be available for a given RO2 radical, the relative rates of which depend on both the structure of RO2 and the ambient conditions. Published kinetics and branching ratio data are reviewed for the bimol. reactions of RO2 with NO, NO2, NO3, OH and HO2; and for their self-reactions and cross-reactions with other RO2 radicals. This information is used to define generic rate coeffs. and structure-activity relationship (SAR) methods that can be applied to the bimol. reactions of a series of important classes of hydrocarbon and oxygenated RO2 radicals. Information for selected unimol. isomerization reactions (i.e. H-atom shift and ring-closure reactions) is also summarized and discussed. The methods presented here are intended to guide the representation of RO2 radical chem. in the next generation of explicit detailed chem. mechanisms.
  49. 49
    McVay, R. C.; Zhang, X.; Aumont, B.; Valorso, R.; Camredon, M.; La, Y. S.; Wennberg, P. O.; Seinfeld, J. H. SOA Formation from the Photooxidation of α-Pinene: Systematic Exploration of the Simulation of Chamber Data. Atmospheric Chem. Phys. 2016, 16 (5), 2785– 2802,  DOI: 10.5194/acp-16-2785-2016
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    SOA formation from the photooxidation of α-pinene: systematic exploration of the simulation of chamber data
    McVay, Renee C.; Zhang, Xuan; Aumont, Bernard; Valorso, Richard; Camredon, Marie; La, Yuyi S.; Wennberg, Paul O.; Seinfeld, John H.
    Atmospheric Chemistry and Physics (2016), 16 (5), 2785-2802CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
    Chem. mechanisms play an important role in simulating the atm. chem. of volatile org. compd. oxidn. Comparison of mechanism simulations with lab. chamber data tests our level of understanding of the prevailing chem. as well as the dynamic processes occurring in the chamber itself. α-Pinene photooxidn. is a well-studied system exptl., for which detailed chem. mechanisms have been formulated. Here, we present the results of simulating low-NO α-pinene photooxidn. expts. conducted in the Caltech chamber with the Generator for Explicit Chem. and Kinetics of Orgs. in the Atm. (GECKO-A) under varying concns. of seed particles and OH levels. Unexpectedly, expts. conducted at low and high OH levels yield the same secondary org. aerosol (SOA) growth, whereas GECKO-A predicts greater SOA growth under high OH levels. SOA formation in the chamber is a result of a competition among the rates of gas-phase oxidn. to low-volatility products, wall deposition of these products, and condensation into the aerosol phase. Various processes - such as photolysis of condensed-phase products, particle-phase dimerization, and peroxy radical autoxidn. - are explored to rationalize the observations. In order to explain the obsd. similar SOA growth at different OH levels, we conclude that vapor wall loss in the Caltech chamber is likely of order 10-5 s-1, consistent with previous exptl. measurements in that chamber.We find that GECKO-A tends to overpredict the contribution to SOA of later-generation oxidn. products under high-OH conditions. Moreover, we propose that autoxidn. may alternatively resolve some or all of the measurement-model discrepancy, but this hypothesis cannot be confirmed until more explicit mechanisms are established for α-pinene autoxidn. The key role of the interplay among oxidn. rate, product volatility, and vapor-wall deposition in chamber expts. is illustrated.
  50. 50
    Galeazzo, T.; Valorso, R.; Li, Y.; Camredon, M.; Aumont, B.; Shiraiwa, M. Estimation of Secondary Organic Aerosol Viscosity from Explicit Modeling of Gas-Phase Oxidation of Isoprene and α-Pinene. Atmospheric Chem. Phys. 2021, 21 (13), 10199– 10213,  DOI: 10.5194/acp-21-10199-2021
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    Estimation of secondary organic aerosol viscosity from explicit modeling of gas-phase oxidation of isoprene and α-pinene
    Galeazzo, Tommaso; Valorso, Richard; Li, Ying; Camredon, Marie; Aumont, Bernard; Shiraiwa, Manabu
    Atmospheric Chemistry and Physics (2021), 21 (13), 10199-10213CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
    Secondary org. aerosols (SOA) are major components of atm. fine particulate matter, affecting climate and air quality. Mounting evidence exists that SOA can adopt glassy and viscous semisolid states, impacting formation and partitioning of SOA. In this study, we apply the GECKO-A (Generator of Explicit Chem. and Kinetics of Orgs. in the Atm.) model to conduct explicit chem. modeling of isoprene photooxidn. and α-pinene ozonolysis and their subsequent SOA formation. The detailed gas-phase chem. schemes from GECKO-A are implemented into a box model and coupled to our recently developed glass transition temp. parameterizations, allowing us to predict SOA viscosity. The effects of chem. compn., relative humidity, mass loadings and mass accommodation on particle viscosity are investigated in comparison with measurements of SOA viscosity. The simulated viscosity of isoprene SOA agrees well with viscosity measurements as a function of relative humidity, while the model underestimates viscosity of α-pinene SOA by a few orders of magnitude. This difference may be due to missing processes in the model, including autoxidn. and particle-phase reactions, leading to the formation of high-molar-mass compds. that would increase particle viscosity. Addnl. simulations imply that kinetic limitations of bulk diffusion and redn. in mass accommodation coeff. may play a role in enhancing particle viscosity by suppressing condensation of semi-volatile compds. The developed model is a useful tool for anal. and investigation of the interplay among gas-phase reactions, particle chem. compn. and SOA phase state.
  51. 51
    Smith, N. R.; Crescenzo, G. V.; Huang, Y.; Hettiyadura, A. P. S.; Siemens, K.; Li, Y.; Faiola, C. L.; Laskin, A.; Shiraiwa, M.; Bertram, A. K.; Nizkorodov, S. A. Viscosity and Liquid–Liquid Phase Separation in Healthy and Stressed Plant SOA. Environ. Sci. Atmospheres 2021, 1 (3), 140– 153,  DOI: 10.1039/D0EA00020E
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    Viscosity and liquid-liquid phase separation in healthy and stressed plant SOA
    Smith, Natalie R.; Crescenzo, Giuseppe V.; Huang, Yuanzhou; Hettiyadura, Anusha P. S.; Siemens, Kyla; Li, Ying; Faiola, Celia L.; Laskin, Alexander; Shiraiwa, Manabu; Bertram, Allan K.; Nizkorodov, Sergey A.
    Environmental Science: Atmospheres (2021), 1 (3), 140-153CODEN: ESANC9; ISSN:2634-3606. (Royal Society of Chemistry)
    Mol. compn., viscosity, and liq.-liq. phase sepn. (LLPS) were investigated for secondary org. aerosol (SOA) derived from synthetic mixts. of volatile org. compds. (VOCs) representing emission profiles for Scots pine trees under healthy and aphid-herbivory stress conditions. Model "healthy plant SOA"and "stressed plant SOA" were generated in a 5 m3 environmental smog chamber by photooxidn. of the mixts. at 50% relative humidity (RH). SOA from photooxidn. of α-pinene was also prepd. for comparison. Mol. compn. was detd. with high resoln. mass spectrometry, viscosity was detd. with the poke-flow technique, and liq.-liq. phase sepn. was investigated with optical microscopy. The stressed plant SOA had increased abundance of higher mol. wt. species, reflecting a greater fraction of sesquiterpenes in the stressed VOC mixt. compared to the healthy plant VOC mixt. LLPS occurred in both the healthy and stressed plant SOA; however, stressed plant SOA exhibited phase sepn. over a broader humidity range than healthy plant SOA, with LLPS persisting down to 23 ± 11% RH. At RH ≤25%, both stressed and healthy plant SOA viscosity exceeded 108 Pa s, a value similar to that of tar pitch. At 40% and 50% RH, stressed plant SOA had the highest viscosity, followed by healthy plant SOA and then α-pinene SOA in descending order. The obsd. peak abundances in the mass spectra were also used to est. the SOA viscosity as a function of RH and volatility. The predicted viscosity of the healthy plant SOA was lower than that of the stressed plant SOA driven by both the higher glass transition temps. and lower hygroscopicity of the org. mols. making up stressed plant SOA. These findings suggest that plant stress influences the physicochem. properties of biogenic SOA. Furthermore, a complex mixt. of VOCs resulted in a higher SOA viscosity compared to SOA generated from α-pinene alone at ≥25% RH, highlighting the importance of studying properties of SOA generated from more realistic multi-component VOC mixts.
  52. 52
    Trump, E. R.; Epstein, S. A.; Riipinen, I.; Donahue, N. M. Wall Effects in Smog Chamber Experiments: A Model Study. Aerosol Sci. Technol. 2016, 50 (11), 1180– 1200,  DOI: 10.1080/02786826.2016.1232858
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    Wall effects in smog chamber experiments: A model study
    Trump, Erica R.; Epstein, Scott A.; Riipinen, Ilona; Donahue, Neil M.
    Aerosol Science and Technology (2016), 50 (11), 1180-1200CODEN: ASTYDQ; ISSN:0278-6826. (Taylor & Francis, Inc.)
    Wall losses of condensable org. vapors are a significant complication for smog-chamber expts. designed to constrain prodn. of Secondary Org. Aerosols (SOA). Here we develop a dynamical mass-balance model based on the Volatility Basis Set (VBS) to explore various pathways for mass transfer between the bulk of a smog-chamber vol. (the vapors and suspended particles) and reservoirs near the chamber walls (deposited and/or nucleated particles on the walls, adsorption to the walls, and sorption into Teflon walls). We consider various limiting cases and explore the sensitivity of inferred SOA yields to assumptions about the actual parameters in a given SOA expt. We also present data suggesting that adsorptive uptake to Teflon for typical SOA is modest. Broadly, we find that walls become a sink for condensable vapors when those vapors interact with either deposited particles of the Teflon walls, with qual. similar effects on the suspended particles. Finally, we show that having a relatively high seed condensation sink is vital to reliable chamber mass balances. Copyright 2016 American Assocn. for Aerosol Research.
  53. 53
    Ye, P.; Ding, X.; Hakala, J.; Hofbauer, V.; Robinson, E. S.; Donahue, N. M. Vapor Wall Loss of Semi-Volatile Organic Compounds in a Teflon Chamber. Aerosol Sci. Technol. 2016, 50 (8), 822– 834,  DOI: 10.1080/02786826.2016.1195905
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    Vapor wall loss of semi-volatile organic compounds in a Teflon chamber
    Ye, Penglin; Ding, Xiang; Hakala, Jani; Hofbauer, Victoria; Robinson, Ellis S.; Donahue, Neil M.
    Aerosol Science and Technology (2016), 50 (8), 822-834CODEN: ASTYDQ; ISSN:0278-6826. (Taylor & Francis, Inc.)
    We have investigated the vapor wall loss of semi-volatile org. compds. (SVOCs) in a Teflon smog chamber. We studied the vapor wall loss of seven SVOCs with known satn. concns., including alkanes (hexacosane, pentacosane, docosane, eicosane, and d62-squalane), an org. acid (oleic acid), and a polyol (levoglucosan) in single-component and binary-component (org.) systems, using ammonium sulfate (AS) seeds to constrain the particle wall loss. We coated inorg. particles with SVOCs and measured the loss of orgs. from those particles to constrain the wall losses, observing loss rates proportional to the satn. concns. of the SVOCs. The loss rate of oleic acid mixed with d62-squalane was proportional to its mole fraction in the mixt. Our results show that the vapor wall-loss rates of SVOCs are significant, quasi-irreversible, and proportional to the SVOC vapor concns. The vapor wall-loss rate const. of the SVOCs that we studied in the CMU chamber is 3.8 ± 0.3 h-1; this is comparable to values in other chambers with similar surface area to vol. ratios. Our results are also consistent with a relatively high mass accommodation coeff. for SVOCs, αorg > 0.1. Copyright 2016 American Assocn. for Aerosol Research.
  54. 54
    Ditto, J. C.; Joo, T.; Khare, P.; Sheu, R.; Takeuchi, M.; Chen, Y.; Xu, W.; Bui, A. A. T.; Sun, Y.; Ng, N. L.; Gentner, D. R. Effects of Molecular-Level Compositional Variability in Organic Aerosol on Phase State and Thermodynamic Mixing Behavior. Environ. Sci. Technol. 2019, 53 (22), 13009– 13018,  DOI: 10.1021/acs.est.9b02664
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    Effects of Molecular-Level Compositional Variability in Organic Aerosol on Phase State and Thermodynamic Mixing Behavior
    Ditto, Jenna C.; Joo, Taekyu; Khare, Peeyush; Sheu, Roger; Takeuchi, Masayuki; Chen, Yunle; Xu, Weiqi; Bui, Alexander A. T.; Sun, Yele; Ng, Nga L.; Gentner, Drew R.
    Environmental Science & Technology (2019), 53 (22), 13009-13018CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    The mol.-level compn. and structure of org. aerosol (OA) affect its physicochem. properties, transformations, and impacts. This work used the mol.-level chem. compn. of functionalized OA from three diverse field sites to evaluate the effect of mol.-level compositional variability on OA phase state and thermodn. mixing favorability. For these ambient sites, modeled aerosol phase state ranged from liq. to semi-solid. OA compn. obsd. variability had some effect on the resulting phase state, but other factors (e.g., the presence of inorg. ions, aerosol liq. water, internal vs. external mixing with water) were detg. factors in whether these particles exist as liqs., semi-solids, or solids. Org. mol. compn. played a more important role in detg. phase state for phase-sepd. (vs. well-mixed) systems. Despite obsd. OA compositional differences, the thermodn. mixing favorability for OA samples with aerosol liq. water, isoprene oxidn. products, or monoterpene oxidn. products remained fairly consistent within each campaign. Mixing of filter-sampled OA and isoprene or monoterpene oxidn. products is often favorable in both seasons, while mixing with water is generally unfavorable.
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    Schervish, M.; Donahue, N. M. Peroxy Radical Chemistry and the Volatility Basis Set. Atmospheric Chem. Phys. 2020, 20 (2), 1183– 1199,  DOI: 10.5194/acp-20-1183-2020
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    Peroxy radical chemistry and the volatility basis set
    Schervish, Meredith; Donahue, Neil M.
    Atmospheric Chemistry and Physics (2020), 20 (2), 1183-1199CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
    Gas-phase autoxidn. of orgs. can generate highly oxygenated org. mols. (HOMs) and thus increase secondary org. aerosol prodn. and enable newparticle formation. Here we present a new implementation of the volatility basis set (VBS) that explicitly resolves peroxy radical (RO2) products formed via autoxidn. The model includes a strong temp. dependence for autoxidn. as well as explicit termination of RO2, including reactions with NO, HO2, and other RO2. The RO2 cross-reactions can produce dimers (ROOR). We explore the temp. and NOx dependence of this chem., showing that temp. strongly influences the intrinsic volatility distribution and that NO can suppress autoxidn. under conditions typically found in the atm.
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    Schervish, M.; Donahue, N. M. Peroxy Radical Kinetics and New Particle Formation. Environ. Sci. Atmospheres 2021, 1 (2), 79– 92,  DOI: 10.1039/D0EA00017E
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    Peroxy radical kinetics and new particle formation
    Schervish, Meredith; Donahue, Neil M.
    Environmental Science: Atmospheres (2021), 1 (2), 79-92CODEN: ESANC9; ISSN:2634-3606. (Royal Society of Chemistry)
    Chamber expts. showing "pure biogenic nucleation" have shown an important role for covalently bound org. assocn. products ("dimers"). These form from peroxy-radical (RO2) cross reactions. Chamber expts. at low-NOx conditions often have quite high hydrocarbon reactant concns. and relatively low concns. of oxygenated volatile org. compds. (OVOCs). This can skew the radical chem. in chambers relative to the real atm., favoring RO2 and disfavoring HO2 radicals. RO2 cross reaction kinetics are in turn highly uncertain. Here we explore the implications of the RO2 to HO2 ratio in chamber expts. as well as the implications of uncertain RO2 cross reaction kinetics and the potential for added CO to mimic more atm. radical conditions. We treat a plausible range of RO2 rate coeffs. under both typical chamber conditions and atm. conditions to see how dimerization is affected by high concns. of OVOCs, and thus lower RO2 : HO2 relative to smog chamber expts. We find that if RO2 reactions are fast, relatively high yields of low volatility dimers can participate in new particle formation. The results are highly sensitive to both the (uncertain) RO2 kinetics as well as RO2 : HO2, suggesting both that low-NOx chamber results should be extrapolated to the atm. with caution but also that the atm. itself may be highly sensitive to the specific (and rich) mixt. of org. compds. and thus peroxy radicals.
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    Abdel-Shafy, H. I.; Mansour, M. S. M. A Review on Polycyclic Aromatic Hydrocarbons: Source, Environmental Impact, Effect on Human Health and Remediation. Egypt. J. Pet. 2016, 25 (1), 107– 123,  DOI: 10.1016/j.ejpe.2015.03.011
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    Kautzman, K. E.; Surratt, J. D.; Chan, M. N.; Chan, A. W. H.; Hersey, S. P.; Chhabra, P. S.; Dalleska, N. F.; Wennberg, P. O.; Flagan, R. C.; Seinfeld, J. H. Chemical Composition of Gas- and Aerosol-Phase Products from the Photooxidation of Naphthalene. J. Phys. Chem. A 2010, 114 (2), 913– 934,  DOI: 10.1021/jp908530s
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    Chemical Composition of Gas- and Aerosol-Phase Products from the Photooxidation of Naphthalene
    Kautzman, K. E.; Surratt, J. D.; Chan, M. N.; Chan, A. W. H.; Hersey, S. P.; Chhabra, P. S.; Dalleska, N. F.; Wennberg, P. O.; Flagan, R. C.; Seinfeld, J. H.
    Journal of Physical Chemistry A (2010), 114 (2), 913-934CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    A detailed evolution of the chem. compn. of the gas- and aerosol-phase constituents produced from OH--initiated photooxidn. of naphthalene under low- and high-NOx conditions is reported. Under high-NOx conditions, ring-opening products are the primary gas-phase products, suggesting the mechanism involves dissocn. of alkoxy radicals (RO) formed via an RO2 + NO pathway, or a bicyclic peroxy mechanism. In contrast to high-NOx chem., ring-retaining compds. appeared to dominate the low-NOx gas-phase products due to the RO2 + HO2 pathway. The authors chem. characterized 53-68% of the secondary org. aerosol (SOA) mass. At. O:C (O:C), H:C, and N:C ratios measured in bulk samples by high-resoln. electro-spray ionization time-of-flight mass spectrometry (HR-ESI-TOFMS) are the same as ratios obsd. with online high-resoln. time-of-flight aerosol mass spectrometry (HR-ToF-AMS), suggesting the chem. compns. and oxidn. levels obsd. in the chem.-characterized fraction of the particle phase are representative of the bulk aerosol. Oligomers, organosulfates (R-OSO3), and other high mol. wt. products were not obsd. in either low- or high-NOx SOA; however, in the presence of a neutral (NH4)2SO4 seed aerosol, an org. sulfonic acid (R-SO3), characterized as hydroxybenzene sulfonic acid, was obsd. in naphthalene SOA produced under high- and low-NOx conditions. Acid compds. and org. peroxides accounted for a large fraction of chem. characterized high- and low-NOx SOA. The authors propose the major gas- and aerosol-phase products obsd. were generated via formation and further reaction of 2-formylcinnamaldehyde or a bicyclic peroxy intermediate. The chem. similarity between lab. SOA and ambient aerosol collected at Birmingham, Alabama, and Pasadena, California, confirmed the importance of polycyclic arom. hydrocarbon oxidn. for aerosol formation in the urban atm.
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    Odinga, E. S.; Waigi, M. G.; Gudda, F. O.; Wang, J.; Yang, B.; Hu, X.; Li, S.; Gao, Y. Occurrence, Formation, Environmental Fate and Risks of Environmentally Persistent Free Radicals in Biochars. Environ. Int. 2020, 134, 105172,  DOI: 10.1016/j.envint.2019.105172
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    Occurrence, formation, environmental fate and risks of environmentally persistent free radicals in biochars
    Odinga, Emmanuel Stephen; Waigi, Michael Gatheru; Gudda, Fredrick Owino; Wang, Jian; Yang, Bing; Hu, Xiaojie; Li, Shunyao; Gao, Yanzheng
    Environment International (2020), 134 (), 105172CODEN: ENVIDV; ISSN:0160-4120. (Elsevier Ltd.)
    Biochars are used globally in agricultural crop prodn. and environmental remediation. However, environmentally persistent free radicals (EPFRs), which are stable emerging pollutants, are generated as a characteristic feature during biomass pyrolysis. EPFRs can induce the formation of reactive oxygen species, which poses huge agro-environmental and human health risks. Their half-lives and persistence in both biochar residues and in the atm. may lead to potentially adverse risks in the environment. This review highlights the comprehensive research into these bioreactive radicals, as well as the bottlenecks of biochar prodn. leading up to the formation and persistence of EPFRs. Addnl., a way forward has been proposed, based on two main recommendations. A global joint initiative to create an all-encompassing regulations policy document that will improve both the technol. and the quality control aspects of biochars to reduce EPFR generation at the prodn. level. Furthermore, environmental impact and risk assessment studies should be conducted in the extensive applications of biochars in order to protect the environmental and human health. The highlighted key research directions proposed herein will shape the prodn., research, and adoption aspects of biochars, which will mitigate the considerable concerns raised on EPFRs.
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    Wei, J.; Fang, T.; Shiraiwa, M. Effects of Acidity on Reactive Oxygen Species Formation from Secondary Organic Aerosols. ACS Environ. Au 2022, 2 (4), 336– 345,  DOI: 10.1021/acsenvironau.2c00018
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    Effects of Acidity on Reactive Oxygen Species Formation from Secondary Organic Aerosols
    Wei, Jinlai; Fang, Ting; Shiraiwa, Manabu
    ACS Environmental Au (2022), 2 (4), 336-345CODEN: AEACC4; ISSN:2694-2518. (American Chemical Society)
    Reactive oxygen species (ROS) play a crit. role in the chem. transformation of atm. secondary org. aerosols (SOA) and aerosol health effects by causing oxidative stress in vivo. Acidity is an important physicochem. property of atm. aerosols, but its effects on the ROS formation from SOA have been poorly characterized. By applying the ESR spin-trapping technique and the Diogenes chemiluminescence assay, we find highly distinct radical yields and compn. at different pH values in the range of 1-7.4 from SOA generated by oxidn. of isoprene, α-terpineol, α-pinene, β-pinene, toluene, and naphthalene. We observe that isoprene SOA has substantial hydroxyl radical (•OH) and org. radical yields at neutral pH, which are 1.5-2 times higher compared to acidic conditions in total radical yields. Superoxide (O2•-) is found to be the dominant species generated by all types of SOAs at lower pH. At neutral pH, α-terpineol SOA exhibits a substantial yield of carbon-centered org. radicals, while no radical formation is obsd. by arom. SOA. Further expts. with model compds. show that the decompn. of org. peroxide leading to radical formation may be suppressed at lower pH due to acid-catalyzed rearrangement of peroxides. We also observe 1.5-3 times higher molar yields of hydrogen peroxide (H2O2) in acidic conditions compared to neutral pH by biogenic and arom. SOA, likely due to enhanced decompn. of α-hydroxyhydroperoxides and quinone redox cycling, resp. These findings are crit. to bridge the gap in understanding ROS formation mechanisms and kinetics in atm. and physiol. environments.
  61. 61
    Kramer, A. J.; Rattanavaraha, W.; Zhang, Z.; Gold, A.; Surratt, J. D.; Lin, Y.-H. Assessing the Oxidative Potential of Isoprene-Derived Epoxides and Secondary Organic Aerosol. Atmos. Environ. 2016, 130, 211– 218,  DOI: 10.1016/j.atmosenv.2015.10.018
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    Assessing the oxidative potential of isoprene-derived epoxides and secondary organic aerosol
    Kramer, Amanda J.; Rattanavaraha, Weruka; Zhang, Zhenfa; Gold, Avram; Surratt, Jason D.; Lin, Ying-Hsuan
    Atmospheric Environment (2016), 130 (), 211-218CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
    Fine particulate matter (PM2.5) is known to contribute to adverse health effects, such as asthma, cardiopulmonary disease, and lung cancer. Secondary org. aerosol (SOA) is a major component of PM2.5 and can be enhanced by atm. oxidn. of biogenic volatile org. compds. in the presence of anthropogenic pollutants, such as nitrogen oxides (NOx) and sulfur dioxide. However, whether biogenic SOA contributes to adverse health effects remains unclear. The objective of this study was to assess the potential of isoprene-derived epoxides and SOA for generating reactive oxygen species (ROS) in light of the recent recognition that atm. oxidn. of isoprene in the presence of acidic sulfate aerosol is a major contributor to the global SOA burden. The dithiothreitol (DTT) assay was used to characterize the ROS generation by the isoprene-derived epoxides, trans-β-isoprene epoxydiol (trans-β-IEPOX) and methacrylic acid epoxide (MAE), and their hydrolysis products, the 2-methyltetrol diastereomers (2-MT), 2-methylglyceric acid (2-MG), their organosulfate derivs., as well as an isoprene-derived hydroxyhydroperoxide (ISOPOOH). In addn., ROS generation potential was evaluated for total SOA produced from photooxidn. of isoprene and methacrolein (MACR) as well as from the reactive uptake of trans-β-IEPOX and MAE onto acidified sulfate aerosol. The high-NOx regime, which yields 2-MG-, MAE- and MACR-derived SOA has a higher ROS generation potential than the low-NOx regime, which yields 2-MT, IEPOX- and isoprene-derived SOA. ISOPOOH has an ROS generation potential similar to 1,4-naphthoquinone (1,4-NQ), suggesting a significant contribution of aerosol-phase org. peroxides to PM oxidative potential. MAE- and MACR-derived SOA show equal or greater ROS generation potential than reported in studies on diesel exhaust PM, highlighting the importance of a comprehensive investigation of the toxicity of isoprene-derived SOA.
  62. 62
    McWhinney, R. D.; Zhou, S.; Abbatt, J. P. D. Naphthalene SOA: Redox Activity and Naphthoquinone Gas–Particle Partitioning. Atmospheric Chem. Phys. 2013, 13 (19), 9731– 9744,  DOI: 10.5194/acp-13-9731-2013
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    Naphthalene SOA: redox activity and naphthoquinone gas-particle partitioning
    McWhinney, R. D.; Zhou, S.; Abbatt, J. P. D.
    Atmospheric Chemistry and Physics (2013), 13 (19), 9731-9744, 14 pp.CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
    Chamber secondary org. aerosol (SOA) from low-NOx photooxidn. of naphthalene by hydroxyl radical was examd. with respect to its redox cycling behavior using the dithiothreitol (DTT) assay. Naphthalene SOA was highly redox-active, consuming DTT at an av. rate of 118 ± 14 pmol per min per μg of SOA material. Measured particle-phase masses of the major previously identified redox active products, 1,2- and 1,4-naphthoquinone, accounted for only 21 ± 3% of the obsd. redox cycling activity. The redox-active 5-hydroxy-1,4-naphthoquinone was identified as a new minor product of naphthalene oxidn., and including this species in redox activity predictions increased the predicted DTT reactivity to 30 ± 5 % of observations. These results suggest that there are substantial unidentified redox-active SOA constituents beyond the small quinones that may be important toxic components of these particles. A gas-to-SOA particle partitioning coeff. was calcd. to be (7.0 ± 2.5) × 10-4 m3 μg-1 for 1,4-naphthoquinone at 25 °C. This value suggests that under typical warm conditions, 1,4-naphthoquinone is unlikely to contribute strongly to redox behavior of ambient particles, although further work is needed to det. the potential impact under conditions such as low temps. where partitioning to the particle is more favorable. Also, higher order oxidn. products that likely account for a substantial fraction of the redox cycling capability of the naphthalene SOA are likely to partition much more strongly to the particle phase.
  63. 63
    Tuet, W. Y.; Chen, Y.; Xu, L.; Fok, S.; Gao, D.; Weber, R. J.; Ng, N. L. Chemical Oxidative Potential of Secondary Organic Aerosol (SOA) Generated from the Photooxidation of Biogenic and Anthropogenic Volatile Organic Compounds. Atmospheric Chem. Phys. 2017, 17 (2), 839– 853,  DOI: 10.5194/acp-17-839-2017
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    Chemical oxidative potential of secondary organic aerosol (SOA) generated from the photooxidation of biogenic and anthropogenic volatile organic compounds
    Tuet, Wing Y.; Chen, Yunle; Xu, Lu; Fok, Shierly; Gao, Dong; Weber, Rodney J.; Ng, Nga L.
    Atmospheric Chemistry and Physics (2017), 17 (2), 839-853CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
    Particulate matter (PM), of which a significant fraction is comprised of secondary org. aerosols (SOA), has received considerable attention due to its health implications. In this study, the water-sol. oxidative potential (OPWS) of SOA generated from the photooxidn. of biogenic and anthropogenic hydrocarbon precursors (isoprene, α-pinene, β-caryophyllene, pentadecane, m-xylene, and naphthalene) under different reaction conditions ("RO2+HO2" vs. "RO2+NO" dominant, dry vs. humid) was characterized using dithiothreitol (DTT) consumption. The measured intrinsic OPWS-DTT values ranged from 9 to 205 pmol min-1 μg-1 and were highly dependent on the specific hydrocarbon precursor, with naphthalene and isoprene SOA generating the highest and lowest OPWS-DTT values, resp. Humidity and RO2 fate affected OPWS-DTT in a hydrocarbon-specific manner, with naphthalene SOA exhibiting the most pronounced effects, likely due to the formation of nitroaroms. Together, these results suggest that precursor identity may be more influential than reaction condition in detg. SOA oxidative potential, demonstrating the importance of sources, such as incomplete combustion, to aerosol toxicity. In the context of other PM sources, all SOA systems, with the exception of naphthalene SOA, were less DTT active than ambient sources related to incomplete combustion, including diesel and gasoline combustion as well as biomass burning. Finally, naphthalene SOA was as DTT active as biomass burning aerosol, which was found to be the most DTT-active OA source in a previous ambient study. These results highlight a need to consider SOA contributions (particularly from anthropogenic hydrocarbons) to health effects in the context of hydrocarbon emissions, SOA yields, and other PM sources.
  64. 64
    Tong, H.; Zhang, Y.; Filippi, A.; Wang, T.; Li, C.; Liu, F.; Leppla, D.; Kourtchev, I.; Wang, K.; Keskinen, H.-M. Radical Formation by Fine Particulate Matter Associated with Highly Oxygenated Molecules. Environ. Sci. Technol. 2019, 53 (21), 12506– 12518,  DOI: 10.1021/acs.est.9b05149
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    Radical Formation by Fine Particulate Matter Associated with Highly Oxygenated Molecules
    Tong, Haijie; Zhang, Yun; Filippi, Alexander; Wang, Ting; Li, Chenpei; Liu, Fobang; Leppla, Denis; Kourtchev, Ivan; Wang, Kai; Keskinen, Helmi-Marja; Levula, Janne T.; Arangio, Andrea M.; Shen, Fangxia; Ditas, Florian; Martin, Scot T.; Artaxo, Paulo; Godoi, Ricardo H. M.; Yamamoto, Carlos I.; de Souza, Rodrigo A. F.; Huang, Ru-Jin; Berkemeier, Thomas; Wang, Yueshe; Su, Hang; Cheng, Yafang; Pope, Francis D.; Fu, Pingqing; Yao, Maosheng; Poehlker, Christopher; Petaejae, Tuukka; Kulmala, Markku; Andreae, Meinrat O.; Shiraiwa, Manabu; Poeschl, Ulrich; Hoffmann, Thorsten; Kalberer, Markus
    Environmental Science & Technology (2019), 53 (21), 12506-12518CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Highly oxygenated mols. (HOMs) play an important role in the formation and evolution of secondary org. aerosols (SOA). However, the abundance of HOMs in different environments and their relation to the oxidative potential of fine particulate matter (PM) are largely unknown. Here, we investigated the relative HOM abundance and radical yield of lab.-generated SOA and fine PM in ambient air ranging from remote forest areas to highly polluted megacities. By ESR and mass spectrometric investigations, we found that the relative abundance of HOMs, esp. the dimeric and low-volatility types, in ambient fine PM was pos. correlated with the formation of radicals in aq. PM exts. SOA from photooxidn. of isoprene, ozonolysis of α- and β-pinene, and fine PM from tropical (central Amazon) and boreal (Hyyti.ovrddot.al.ovrddot.a, Finland) forests exhibited a higher HOM abundance and radical yield than SOA from photooxidn. of naphthalene and fine PM from urban sites (Beijing, Guangzhou, Mainz, Shanghai, and Xi'an), confirming that HOMs are important constituents of biogenic SOA to generate radicals. Our study provides new insights into the chem. relationship of HOM abundance, compn., and sources with the yield of radicals by lab. and ambient aerosols, enabling better quantification of the component-specific contribution of source- or site-specific fine PM to its climate and health effects.
  65. 65
    Grosjean, D.; Grosjean, E.; Williams, E. L. Thermal Decomposition of PAN, PPN and Vinyl-PAN. Air Waste 1994, 44 (4), 391– 396,  DOI: 10.1080/1073161X.1994.10467260
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    Thermal decomposition of PAN, PPN and vinyl-PAN
    Grosjean, Daniel; Grosjean, Eric; Williams, Edwin L.
    Air & Waste (1994), 44 (4), 391-6CODEN: AIWAE2; ISSN:1073-161X.
    The gas phase thermal decompn. rates of the C1 and C2-substituted peroxyacyl nitrates (RC(O)OONO2), PAN (R=CH3), PPN (R=C2H5) and vinyl-PAN (R= CH2=CH-) were measured at 288-299 K and 1 atm. of air. The results for PAN are consistent with literature data. Thermal decompn. rates for PPN and vinyl-PAN are similar to that for PAN, with k298 = 3.0 × 10-4/s for PAN, 3.4 × 10-4/s for PPN, and 3.0 × 10-4/s for vinyl-PAN. Implications for the atm. persistence of PPN and vinyl-PAN as compared to that of PAN are discussed.
  66. 66
    von Ahsen, S.; Willner, H.; Francisco, J. S. Thermal Decomposition of Peroxy Acetyl Nitrate CH3C(O)OONO2. J. Chem. Phys. 2004, 121 (5), 2048– 2057,  DOI: 10.1063/1.1767813
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    Thermal decomposition of peroxy acetyl nitrate CH3C(O)OONO2
    von Ahsen, Stefan; Willner, Helge; Francisco, Joseph S.
    Journal of Chemical Physics (2004), 121 (5), 2048-2057CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    The thermal decompn. of peroxy acetyl nitrate (PAN) is investigated by low pressure flash thermolysis of PAN highly dild. in noble gases and subsequent isolation of the products in noble gas matrixes at low temps. and by d. functional computations. The IR spectroscopically obsd. formation of CH3C(O)OO and H2CCO (ketene) besides NO2, CO2, and HOO implies a unimol. decay pathway for the thermal decompn. of PAN. The major decompn. reaction of PAN is bond fission of the O-N single bond yielding the peroxy radical. The O-O bond fission pathway is a minor route. In the latter case the primary reaction products undergo secondary reactions whose products are spectroscopically identified. No evidence for rearrangement processes as the formation of Me nitrate is obsd. A detailed mapping of the reaction pathways for primary and secondary reactions using quantum chem. calcns. is in good agreement with the expt. and predicts homolytic O-N and O-O bond fissions within the PAN mol. as the lowest energetic primary processes. In addn., the first IR spectroscopic characterization of two rotameric forms for the radical CH3C(O)OO is given.
  67. 67
    Bunce, N. J.; Liu, L.; Zhu, J.; Lane, D. A. Reaction of Naphthalene and Its Derivatives with Hydroxyl Radicals in the Gas Phase. Environ. Sci. Technol. 1997, 31 (8), 2252– 2259,  DOI: 10.1021/es960813g
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    Reaction of Naphthalene and Its Derivatives with Hydroxyl Radicals in the Gas Phase
    Bunce, Nigel J.; Liu, Lina; Zhu, Jiang; Lane, Douglas A.
    Environmental Science and Technology (1997), 31 (8), 2252-2259CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Naphthalene is the most abundant polycyclic arom. hydrocarbon (PAH) found in urban air. It is reactive in the atm. under ambient conditions, its chief reaction partner being the hydroxyl radical, OH•. In this work, the reactions of OH• with naphthalene, 1- and 2-naphthol, and 1- and 2-nitronaphthalene were studied in a 9.4 m3 smog chamber. Relative rates of reaction accorded well with previous studies and allowed ests. to be made of the atm. lifetimes of these compds. Numerous oxidn. products were identified, and mechanisms proposed for their formation were based on the further transformation of benzocyclohexadienyl radicals formed by addn. of OH• to naphthalene. The naphthols and nitronaphthalenes were deduced not to be on the major reaction pathway to the more oxidized products. Because of the high reactivity of PAH in air, we suggest that priority be given to identifying and quantitating their reaction products, some of which may be relatively persistent air toxics.
  68. 68
    Nozière, B.; Barnes, I.; Becker, K.-H. Product Study and Mechanisms of the Reactions of α-Pinene and of Pinonaldehyde with OH Radicals. J. Geophys. Res. Atmospheres 1999, 104 (D19), 23645– 23656,  DOI: 10.1029/1999JD900778
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    Product study and mechanisms of the reactions of α-pinene and of pinonaldehyde with OH radicals
    Noziere, Barbara; Barnes, Ian; Becker, Karl-Heinz
    Journal of Geophysical Research, [Atmospheres] (1999), 104 (D19), 23645-23656CODEN: JGRDE3 ISSN:. (American Geophysical Union)
    The reactions of α-pinene and of its main oxidn. product, pinonaldehyde (3-acetyl-2,2-dimethyl-cyclobutyl-ethanal), with OH radicals have been studied in the lab. using Fourier transform IR spectroscopy for real-time monitoring of the gas-phase chem. species and a Scanning Mobility Particle Sizer system (3071 A, TSI) for the study of the secondary aerosol formation. All gas-phase molar yields were quantified using calibrated ref. of the pure compd., except for the nitrates products. The results were: for the α-pinene expts. in the presence of NOx, pinonaldehyde, (87 ± 20)%; total nitrates (18 ± 9)%; formaldehyde, (23 ± 9)%; acetone (9 ± 6)%; for the α-pinene expts. in the absence of NOx: pinonaldehyde, (37 ± 7)%; formaldehyde, (8 ± 1)%; acetone, (7 ± 2)%; for the pinonaldehyde expts. in the presence of nitric oxide, formaldehyde (152 ± 56)% and acetone (15 ± 7)%. The aerosol measurements showed that the condensed products accounted for the missing carbon in the gas-phase balance. The partitioning of the products into the condensed phase was found to be potentially significant under exptl. conditions but less than 10% for initial α-pinene concns. lower than 1013 mol. cm-3 and hence negligible under atm. conditions in the absence of aerosol seeds. On the basis of these results a comprehensive mechanism for the gas-phase reaction of α-pinene with OH in the presence of NOx has been proposed, including quant. values for all the involved branching ratios.
  69. 69
    Romonosky, D. E.; Laskin, A.; Laskin, J.; Nizkorodov, S. A. High-Resolution Mass Spectrometry and Molecular Characterization of Aqueous Photochemistry Products of Common Types of Secondary Organic Aerosols. J. Phys. Chem. A 2015, 119 (11), 2594– 2606,  DOI: 10.1021/jp509476r
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    High-Resolution Mass Spectrometry and Molecular Characterization of Aqueous Photochemistry Products of Common Types of Secondary Organic Aerosols
    Romonosky, Dian E.; Laskin, Alexander; Laskin, Julia; Nizkorodov, Sergey A.
    Journal of Physical Chemistry A (2015), 119 (11), 2594-2606CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    This work presents a systematic assessment of the mol. level compn. and extent of aq. photochem. processing in different types of secondary org. aerosols (SOA) from biogenic and anthropogenic precursors, including α-pinene, β-pinene, β-myrcene, D-limonene, α-humulene, 1,3,5-trimethylbenzene, and guaiacol, oxidized by O3 (simulating a remote atm.) or by OH- in the presence of NOx (simulating an urban atm.). Chamber- and flow-tube-generated SOA samples were collected, extd. in a methanol/water soln., and photolyzed for 1 h under identical irradn. conditions. In these expts., irradn. was equiv. to ∼3-8 h exposure to the sun at its zenith. The mol. level compn. of dissolved SOA was probed before and after photolysis with direct-infusion electro-spray ionization high-resoln. mass spectrometry. Mass spectra of un-photolyzed SOA generated by O3 oxidn. of monoterpenes showed qual. similar features and contained largely overlapping subsets of identified compds. Mass spectra of OH-/NOx-generated SOA had a more unique visual appearance and indicated a lower extent of product overlap. The fraction of N-contg. species (organonitrates, nitroaroms.) was highly sensitive to the SOA precursor. These observations suggested that attributing high-resoln. mass spectra in field SOA samples to specific SOA precursors should be more straight-forward under OH-/NOx oxidn. conditions vs. O3-driven oxidn. Comparing SOA constituents before and after photolysis showed a tendency to reduce the av. no. of atoms in the SOA compds. without a significant effect on overall O:C and H:C ratios. SOA prepd. by OH-/NOx photooxidn. of 1,3,5-trimethylbenzene and guaiacol were more resilient to photolysis despite being the most light-absorbing. The compn. of SOA prepd. by ozonolysis of monoterpenes changed more significantly as a result of photolysis. Results indicated aq. photolysis of dissolved SOA compds. in cloud/fog water can occur in various types of SOA and on atmospherically relevant time scales. However, the extent of the photolysis-driven changes in mol. compn. depended on the specific type of SOA.
  70. 70
    Romonosky, D. E.; Li, Y.; Shiraiwa, M.; Laskin, A.; Laskin, J.; Nizkorodov, S. A. Aqueous Photochemistry of Secondary Organic Aerosol of α-Pinene and α-Humulene Oxidized with Ozone, Hydroxyl Radical, and Nitrate Radical. J. Phys. Chem. A 2017, 121 (6), 1298– 1309,  DOI: 10.1021/acs.jpca.6b10900
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    Aqueous Photochemistry of Secondary Organic Aerosol of α-Pinene and α-Humulene Oxidized with Ozone, Hydroxyl Radical, and Nitrate Radical
    Romonosky, Dian E.; Li, Ying; Shiraiwa, Manabu; Laskin, Alexander; Laskin, Julia; Nizkorodov, Sergey A.
    Journal of Physical Chemistry A (2017), 121 (6), 1298-1309CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    Formation of secondary org. aerosols (SOA) from biogenic volatile org. compds. (BVOC) occurs via O3- and OH-initiated reactions during the day and reactions with NO3 during the night. We explored the effect of these three oxidn. conditions on the mol. compn. and aq. photochem. of model SOA prepd. from two common BVOC. A common monoterpene, α-pinene, and sesquiterpene, α-humulene, were used to form SOA in a smog chamber via BVOC + O3, BVOC + NO3, and BVOC + OH + NOx oxidn. Samples of SOA were collected on filters, water-sol. compds. from SOA were extd. in water, and the resulting aq. solns. were photolyzed to simulate the photochem. aq. processing of SOA. The extent of change in the mol. level compn. of SOA over 4 h of photolysis (approx. equiv. to 64 h of photolysis under ambient conditions) was assessed with high-resoln. electrospray ionization mass spectrometry. The anal. revealed significant differences in the mol. compn. between SOA formed by the different oxidn. pathways. The compn. further evolved during photolysis with the most notable change corresponding to the nearly complete removal of nitrogen-contg. org. compds. Hydrolysis of SOA compds. also occurred in parallel with photolysis. The preferential loss of larger SOA compds. during photolysis and hydrolysis made the SOA compds. more volatile on av. This study suggests that aq. processes may under certain conditions lead to a redn. in the SOA loading as opposed to an increase in SOA loading commonly assumed in the literature.
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    Siemens, K.; Morales, A.; He, Q.; Li, C.; Hettiyadura, A. P. S.; Rudich, Y.; Laskin, A. Molecular Analysis of Secondary Brown Carbon Produced from the Photooxidation of Naphthalene. Environ. Sci. Technol. 2022, 56 (6), 3340– 3353,  DOI: 10.1021/acs.est.1c03135
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    Molecular Analysis of Secondary Brown Carbon Produced from the Photooxidation of Naphthalene
    Siemens, Kyla; Morales, Ana; He, Quanfu; Li, Chunlin; Hettiyadura, Anusha P. S.; Rudich, Yinon; Laskin, Alexander
    Environmental Science & Technology (2022), 56 (6), 3340-3353CODEN: ESTHAG; ISSN:1520-5851. (American Chemical Society)
    We investigate the chem. compn. of org. light-absorbing components, also known as brown carbon (BrC) chromophores, formed in a proxy of anthropogenic secondary org. aerosol generated from the photooxidn. of naphthalene (naph-SOA) in the absence and presence of NOx. High-performance liq. chromatog. equipped with a photodiode array detector and electrospray ionization high-resoln. mass spectrometer is employed to characterize naph-SOA and its BrC components. We provide mol.-level insights into the chem. compn. and optical properties of individual naph-SOA components and investigate their BrC relevance. This work reveals the formation of strongly absorbing nitro-arom. chromophores under high-NOx conditions and describes their degrdn. during atm. aging. NOx addn. enhanced the light absorption of naph-SOA while reducing wavelength-dependence, as seen by the mass absorption coeff. (MAC) and absorption Ångstr.ovrddot.om exponent (AAE). Optical parameters of naph-SOA generated under low- and high-NOx conditions showed a range of values from MACOM 405nm ~ 0.12 m2 g-1 and AAE300-450nm ~ 8.87 (low-NOx) to MACOM 405nm ~ 0.19 m2 g-1 and AAE300-450nm ~ 7.59 (high-NOx), consistent with "very weak" and "weak" BrC optical classes, resp. The weak-BrC class is commonly attributed to biomass smoldering emissions, which appear to have optical properties comparable with the naph-SOA. Mol. chromophores contributing to naphthalene BrC absorption were identified with substantial nitro-aroms., indicating that these species may be used as source-specific markers of BrC related to the anthropogenic emissions.
  72. 72
    Lee, H. J.; Aiona, P. K.; Laskin, A.; Laskin, J.; Nizkorodov, S. A. Effect of Solar Radiation on the Optical Properties and Molecular Composition of Laboratory Proxies of Atmospheric Brown Carbon. Environ. Sci. Technol. 2014, 48 (17), 10217– 10226,  DOI: 10.1021/es502515r
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    Effect of solar radiation on the optical properties and molecular composition of laboratory proxies of atmospheric brown carbon
    Lee, Hyun Ji; Aiona, Paige Kuuipo; Laskin, Alexander; Laskin, Julia; Nizkorodov, Sergey A.
    Environmental Science & Technology (2014), 48 (17), 10217-10226CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Sources, optical properties, and chem. compn. of atm. brown carbon (BrC) aerosol are uncertain, making it challenging to est. its contribution to radiative forcing. Furthermore, optical properties of BrC may change significantly during its atm. aging. We examd. the effect of photolysis on the mol. compn., mass absorption coeff., and fluorescence of secondary org. aerosol (SOA) prepd. by high-NOx photooxidn. of naphthalene (NAP SOA). Our expts. were designed to model photolysis processes of NAP SOA compds. dissolved in cloud or fog droplets. Aq. solns. of NAP SOA were obsd. to photobleach (i.e., lose their ability to absorb visible radiation) with an effective half-life of ∼15 h (with sun in its zenith) for the loss of near-UV (300-400 nm) absorbance. The mol. compn. of NAP SOA was significantly modified by photolysis, with the av. SOA formula changing from C14.1H14.5O5.1N0.085 to C11.8H14.9O4.5N0.023 after 4 h of irradn. However, the av. O/C ratio did not change significantly, suggesting that it is not a good metric for assessing the extent of photolysis-driven aging in NAP SOA (and in BrC in general). In contrast to NAP SOA, the photobleaching of BrC material produced by the reaction of limonene + ozone SOA with ammonia vapor (aged LIM/O3 SOA) was much faster, but it did not result in a significant change in av. mol. compn. The characteristic absorbance of the aged LIM/O3 SOA in the 450-600 nm range decayed with an effective half-life of <0.5 h. These results emphasize the highly variable and dynamic nature of different types of atm. BrC.
  73. 73
    Vasquez, K. T.; Crounse, J. D.; Schulze, B. C.; Bates, K. H.; Teng, A. P.; Xu, L.; Allen, H. M.; Wennberg, P. O. Rapid Hydrolysis of Tertiary Isoprene Nitrate Efficiently Removes NOx from the Atmosphere. Proc. Natl. Acad. Sci. U. S. A. 2020, 117 (52), 33011– 33016,  DOI: 10.1073/pnas.2017442117
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    Rapid hydrolysis of tertiary isoprene nitrate efficiently removes NOx from the atmosphere
    Vasquez, Krystal T.; Crounse, John D.; Schulze, Benjamin C.; Bates, Kelvin H.; Teng, Alexander P.; Xu, Lu; Allen, Hannah M.; Wennberg, Paul O.
    Proceedings of the National Academy of Sciences of the United States of America (2020), 117 (52), 33011-33016CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
    The formation of a suite of isoprene-derived hydroxy nitrate (IHN) isomers during the OH-initiated oxidn. of isoprene affects both the concn. and distribution of nitrogen oxide free radicals (NOx). Expts. performed in an atm. simulation chamber suggest that the lifetime of the most abundant isomer, 1,2-IHN, is shortened significantly by a water-mediated process (leading to nitric acid formation), while the lifetime of a similar isomer, 4,3-IHN, is not. Consistent with these chamber studies, NMR kinetic expts. constrain the 1,2-IHN hydrolysis lifetime to \<10 s in deuterium oxide (D2O) at 298 K, whereas the 4,3-IHN isomer was obsd. to hydrolyze much less efficiently. These lab. findings are used to interpret observations of the IHN isomer distribution in ambient air. The IHN isomer ratio (1,2-IHN to 4,3-IHN) in a high NOx environment decreases rapidly in the afternoon, which is not explained using known gas-phase chem. When simulated with an observationally constrained model, we find that an addnl. loss process for the 1,2-IHN isomer with a time const. of ∼6 h best explains our atm. measurements. Using ests. for 1,2-IHN Henry's law const. and atm. liq. water vol., we show that condensed-phase hydrolysis of 1,2-IHN can account for this loss process. Simulations from a global chem. transport model show that the hydrolysis of 1,2-IHN accounts for a substantial fraction of NOx lost (and HNO3 produced), resulting in large impacts on oxidant formation, esp. over forested regions.
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    Kurtén, T.; Rissanen, M. P.; Mackeprang, K.; Thornton, J. A.; Hyttinen, N.; Jørgensen, S.; Ehn, M.; Kjaergaard, H. G. Computational Study of Hydrogen Shifts and Ring-Opening Mechanisms in α-Pinene Ozonolysis Products. J. Phys. Chem. A 2015, 119 (46), 11366– 11375,  DOI: 10.1021/acs.jpca.5b08948
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    Computational Study of Hydrogen Shifts and Ring-Opening Mechanisms in α-Pinene Ozonolysis Products
    Kurten, Theo; Rissanen, Matti P.; Mackeprang, Kasper; Thornton, Joel A.; Hyttinen, Noora; Joergensen, Solvejg; Ehn, Mikael; Kjaergaard, Henrik G.
    Journal of Physical Chemistry A (2015), 119 (46), 11366-11375CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    Autoxidn. by sequential peroxy radical hydrogen shifts (H-shifts) and O2 addns. has recently emerged as a promising mechanism for the rapid formation of highly oxidized, low-volatility org. compds. in the atm. A key prerequisite for autoxidn. is that the H-shifts of the initial peroxy radicals formed by, e.g., OH or O3 oxidn. are fast enough to compete with bimol. sink reactions. In most atm. conditions, these restrict the lifetime of peroxy radicals to be on the order of seconds. We have systematically investigated all potentially important (nonmethyl, sterically unhindered) H-shifts of all four peroxy radicals formed in the ozonolysis of α-pinene using d. functional (ωB97XD) and coupled cluster [CCSD(T)-F12] theory. In contrast to the related but chem. simpler cyclohexene ozonolysis system, none of the calcd. H-shifts have rate consts. above 1 s-1 at 298 K, and most are below 0.01 s-1. The low rate consts. are connected to the presence of the strained cyclobutyl ring in the α-pinene-derived peroxy radicals, which hinders H-shifts both from and across the ring. For autoxidn. to yield the exptl. obsd. highly oxidized products in the α-pinene ozonolysis system, addnl. ring-opening reaction mechanisms breaking the cyclobutyl ring are therefore needed. We further investigate possible uni- and bimol. pathways for opening the cyclobutyl ring in the α-pinene ozonolysis system.
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    Li, Y.; Shiraiwa, M. Timescales of Secondary Organic Aerosols to Reach Equilibrium at Various Temperatures and Relative Humidities. Atmospheric Chem. Phys. 2019, 19 (9), 5959– 5971,  DOI: 10.5194/acp-19-5959-2019
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    Timescales of secondary organic aerosols to reach equilibrium at various temperatures and relative humiditie
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    Secondary org. aerosols (SOA) account for a substantial fraction of air particulate matter, and SOA formation is often modeled assuming rapid establishment of gas-particle equil. Here, we est. the characteristic timescale for SOA to achieve gas-particle equil. under a wide range of temps. and relative humidities using a state-of-the-art kinetic flux model. Equilibration timescales were calcd. by varying particle phase state, size, mass loadings, and volatility of org. compds. in open and closed systems. Model simulations suggest that the equilibration timescale for semi-volatile compds. is on the order of seconds or minutes for most conditions in the planetary boundary layer, but it can be longer than 1 h if particles adopt glassy or amorphous solid states with high glass transition temps. at low relative humidity. The timescale of partitioning of low-volatile compds. into highly viscous particles is shorter compared to semi-volatile compds. in the closed system, as it is largely detd. by condensation sink due to very slow re-evapn. with relatively quick establishment of local equil. between the gas phase and the near-surface bulk. The dependence of equilibration timescales on both volatility and bulk diffusivity provides crit. insights into thermodn. or kinetic treatments of SOA partitioning for accurate predictions of gas- and particle-phase concns. of semi-volatile compds. in regional and global chem. transport models.
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    Shiraiwa, M.; Pöschl, U. Mass Accommodation and Gas–Particle Partitioning in Secondary Organic Aerosols: Dependence on Diffusivity, Volatility, Particle-Phase Reactions, and Penetration Depth. Atmospheric Chem. Phys. 2021, 21 (3), 1565– 1580,  DOI: 10.5194/acp-21-1565-2021
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    Mass accommodation and gas-particle partitioning in secondary organic aerosols: dependence on diffusivity, volatility, particle-phase reactions, and penetration depth
    Shiraiwa, Manabu; Poeschl, Ulrich
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    Mass accommodation is an essential process for gas-particle partitioning of org. compds. in secondary org. aerosols (SOA). The mass accommodation coeff. is commonly described as the probability of a gas mol. colliding with the surface to enter the particle phase. It is often applied, however, without specifying if and how deep a mol. has to penetrate beneath the surface to be regarded as being incorporated into the condensed phase (adsorption vs. absorption). While this aspect is usually not crit. for liq. particles with rapid surface-bulk exchange, it can be important for viscous semi-solid or glassy solid particles to distinguish and resolve the kinetics of accommodation at the surface, transfer across the gas-particle interface, and further transport into the particle bulk. For this purpose, we introduce a novel parameter: an effective mass accommodation coeff. aeff that depends on penetration depth and is a function of surface accommodation coeff., volatility, bulk diffusivity, and particlephase reaction rate coeff. Application of aeff in the traditional Fuchs-Sutugin approxn. of mass-transport kinetics at the gas-particle interface yields SOA partitioning results that are consistent with a detailed kinetic multilayer model (kinetic multilayer model of gas-particle interactions in aerosols and clouds, KM-GAP; Shiraiwa et al., 2012) and two-film model solns. (Model for Simulating Aerosol Interactions and Chem., MOSAIC; Zaveri et al., 2014) but deviate substantially from earlier modeling approaches not considering the influence of penetration depth and related parameters. For highly viscous or semi-solid particles, we show that the effective mass accommodation coeff. remains similar to the surface accommodation coeff. in the case of low-volatility compds., whereas it can decrease by several orders of magnitude in the case of semi-volatile compds. Such effects can explain apparent inconsistencies between earlier studies deriving mass accommodation coeffs. from exptl. data or from mol. dynamics simulations. Our findings challenge the approach of traditional SOA models using the Fuchs-Sutugin approxn. of mass transfer kinetics with a fixed mass accommodation coeff., regardless of particle phase state and penetration depth. The effective mass accommodation coeff. introduced in this study provides an efficient new way of accounting for the influence of volatility, diffusivity, and particle-phase reactions on SOA partitioning in process models as well as in regional and global air quality models. While kinetic limitations may not be crit. for partitioning into liq. SOA particles in the planetary boundary layer (PBL), the effects are likely important for amorphous semi-solid or glassy SOA in the free and upper troposphere (FT-UT) as well as in the PBL at low relative humidity and low temp.
  77. 77
    Zhang, Y.; Chen, Y.; Lambe, A. T.; Olson, N. E.; Lei, Z.; Craig, R. L.; Zhang, Z.; Gold, A.; Onasch, T. B.; Jayne, J. T. Effect of the Aerosol-Phase State on Secondary Organic Aerosol Formation from the Reactive Uptake of Isoprene-Derived Epoxydiols (IEPOX). Environ. Sci. Technol. Lett. 2018, 5 (3), 167– 174,  DOI: 10.1021/acs.estlett.8b00044
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    Effect of the Aerosol-Phase State on Secondary Organic Aerosol Formation from the Reactive Uptake of Isoprene-Derived Epoxydiols (IEPOX)
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    Environmental Science & Technology Letters (2018), 5 (3), 167-174CODEN: ESTLCU; ISSN:2328-8930. (American Chemical Society)
    Acid-catalyzed reactions between gas- and particle-phase constituents are crit. to atm. secondary org. aerosol (SOA) formation. The aerosol-phase state is thought to influence the reactive uptake of gas-phase precursors to aerosol particles by altering diffusion rates within particles. However, few exptl. studies have explored the precise role of the aerosol-phase state on reactive uptake processes. This lab. study systematically examines the reactive uptake coeff. (γ) of trans-β-isoprene epoxydiol (trans-β-IEPOX), the predominant IEPOX isomer, on acidic sulfate particles coated with SOA derived from α-pinene ozonolysis. γIEPOX is obtained for core-shell particles, the morphol. of which was confirmed by microscopy, as a function of SOA coating thickness and relative humidity. γIEPOX is reduced, in some cases by half of the original value, when SOA coatings are present prior to uptake, esp. when coating thicknesses are >15 nm. The diurnal trend of IEPOX lost to acid-catalyzed reactive uptake yielding SOA compared with other known atm. sinks (gas-phase oxidn. or deposition) is derived by modeling the exptl. coating effect with field data from the southeastern United States. IEPOX-derived SOA is estd. to be reduced by 16-27% due to preexisting org. coatings during the afternoon (12:00 to 7:00 p.m., local time), corresponding to the period with the highest level of prodn.
  78. 78
    Huang, Y.; Mahrt, F.; Xu, S.; Shiraiwa, M.; Zuend, A.; Bertram, A. K. Coexistence of Three Liquid Phases in Individual Atmospheric Aerosol Particles. Proc. Natl. Acad. Sci. U. S. A. 2021, 118 (16), e2102512118,  DOI: 10.1073/pnas.2102512118
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    Coexistence of three liquid phases in individual atmospheric aerosol particles
    Huang, Yuanzhou; Mahrt, Fabian; Xu, Shaun; Shiraiwa, Manabu; Zuend, Andreas; Bertram, Allan K.
    Proceedings of the National Academy of Sciences of the United States of America (2021), 118 (16), e2102512118CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
    Individual atm. particles can contain mixts. of primary org. aerosol (POA), secondary org. aerosol (SOA), and secondary inorg. aerosol (SIA). To predict the role of such complex multicomponent particles in air quality and climate, information on the no. and types of phases present in the particles is needed. However, the phase behavior of such particles has not been studied in the lab., and as a result, remains poorly constrained. Here, we show that POA+SOA+SIA particles can contain three distinct liq. phases: a low-polarity org.-rich phase, a higher-polarity org.-rich phase, and an aq. inorg.-rich phase. Based on our results, when the elemental oxygen-to-carbon (O:C) ratio of the SOA is \<0.8, three liq. phases can coexist within the same particle over a wide relative humidity range. In contrast, when the O:C ratio of the SOA is greater than 0.8, three phases will not form. We also demonstrate, using thermodn. and kinetic modeling, that the presence of three liq. phases in such particles impacts their equilibration timescale with the surrounding gas phase. Three phases will likely also impact their ability to act as nuclei for liq. cloud droplets, the reactivity of these particles, and the mechanism of SOA formation and growth in the atm. These observations provide fundamental information necessary for improved predictions of air quality and aerosol indirect effects on climate.

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  • Abstract

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    Figure 1

    Figure 1. (a) EPFR concentrations in naphthalene SOA generated under low and high NOx conditions after 30 min of sample collection. (b) Decay of EPFR in naphthalene SOA generated under low (dark gray) and high NOx (light gray) conditions over the span of 80 min after SOA collection.

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    Figure 2

    Figure 2. Abundance of C10H6O2+ compounds in naphthalene SOA as determined by high-resolution mass spectrometry.

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    Figure 3

    Figure 3. Molar yields of BMPO radical adducts (BMPO-OH, BMPO-OOH, BMPO-OR, and BMPO-R) in water extracts of (a) α-pinene and (b) naphthalene SOA generated under low and high NOx conditions.

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    Figure 4

    Figure 4. (a) Total peroxide concentrations and (b) DTT activities of α-pinene and naphthalene SOA produced under low and high NOx conditions. Error bars represent the standard deviation.

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    Figure 5

    Figure 5. (a) Functional group distributions in α-pinene SOA simulated by the GECKO-A box model for the photooxidation of α-pinene under low and high NOx conditions. (b) Modeled concentrations of organic hydroperoxides and organic nitrates from α-pinene oxidation under low and high NOx conditions by r2D-VBS. The green bars represent OOH formation with an allowed production of one peroxide per molecule, whereas the blue bars represent OOH formation with OOH production at each step of autoxidation. The red bar represents the organic nitrate formation in the presence of NOx.

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    Figure 6

    Figure 6. High-resolution mass spectra and intensity-normalized average elemental ratios for (a) naphthalene (NAP) low NOx SOA, (b) NAP high NOx SOA, (c) α-pinene (APIN) low NOx SOA, and (d) APIN high NOx SOA. Compounds containing only carbon, hydrogen, and oxygen (CHO) are shown in black while compounds containing carbon, hydrogen, oxygen, and nitrogen (CHON) are shown in red.

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    Figure 7

    Figure 7. Double-bond equivalents as a function of carbon number for (a) naphthalene SOA and (b) α-pinene. SOA formed under high NOx conditions, excluding nitrogen-containing compounds, is shown in red circles, and SOA formed under low NOx conditions is shown in black squares. Marker size is scaled to the relative summed intensity at each point.

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      There is no corresponding record for this reference.
    9. 9
      Cox, R. A.; Derwent, R. G.; Williams, M. R. Atmospheric Photooxidation Reactions. Rates, Reactivity, and Mechanism for Reaction of Organic Compounds with Hydroxyl Radicals. Environ. Sci. Technol. 1980, 14 (1), 57– 61,  DOI: 10.1021/es60161a007
      9
      Atmospheric photooxidation reactions. Rates, reactivity, and mechanism for reaction of organic compounds with hydroxyl radicals
      Cox, Richard A.; Derwent, Richard G.; Williams, Michael R.
      Environmental Science and Technology (1980), 14 (1), 57-61CODEN: ESTHAG; ISSN:0013-936X.
      The photooxidn. of a no. of org. species, representing several classes of atm. pollutants, has been studied in the presence of HONO, NO, and NO2 at ppm concns. The expts. give information on the rate and mechanism of the reaction with org. mols. of HO radicals produced by photolysis of HONO under these conditions. The data allow evaluation of relative rate consts. for the reaction of HO with these org. species and the stoichiometry for NO to NO2 conversion during the subsequent oxidn. steps. The implications of the results for the assessment of the atm. reactivity of org. pollutants with respect to photooxidant formation are briefly discussed.
    10. 10
      Suzen, S.; Gurer-Orhan, H.; Saso, L. Detection of Reactive Oxygen and Nitrogen Species by Electron Paramagnetic Resonance (EPR) Technique. Mol. Basel Switz. 2017, 22 (1), E181
      There is no corresponding record for this reference.
    11. 11
      Guenther, A. A Global Model of Natural Volatile Organic Compound Emissions. J. Geophys. Res. 1995, 100 (D5), 8873– 8892,  DOI: 10.1029/94JD02950
      11
      A global model of natural volatile organic compound emissions
      Guenther, Alex; Hewitt, C. Nicholas; Erickson, David; Fall, Ray; Geron, Chris; Graedel, Tom; Harley, Peter; Klinger, Lee; Lerdau, Manuel; et al.
      Journal of Geophysical Research, [Atmospheres] (1995), 100 (D5), 8873-92CODEN: JGRDE3 ISSN:. (American Geophysical Union)
      Numerical assessments of global air quality and potential changes in atm. chem. constituents require ests. of the surface fluxes of a variety of trace gas species. A global model is developed to est. emissions of volatile org. compds. from natural sources (NVOC). Methane is not considered here and has been described in detail elsewhere. The model has a highly resolved spatial grid (0.5° × 0.5° latitude/longitude) and generates hourly av. emission ests. Chem. species are grouped into four categories: isoprene, monoterpenes, other reactive VOC (ORVOC), and other VOC (OVOC). NVOC emissions from oceans are estd. as a function of geophys. variables from a general circulation model and ocean color satellite data. Emissions from plant foliage are estd. from ecosystem specific biomass and emission factors and algorithms describing light and temp. dependence of NVOC emissions. Foliar d. ests. are based on climatic variables and satellite data. Temporal variations in the model are driven by monthly ests. of biomass and temp. and hourly light ests. The annual global VOC flux is estd. to be 1150 Tg C, composed of 44% isoprene, 11% monoterpenes, 22.5% other reactive VOC, and 22.5% other VOC. Large uncertainties exist for each of these ests. and particularly for compds. other than isoprene and monoterpenes. Tropical woodlands (rain forest, seasonal, drought-deciduous, and savanna) contribute about half of all global natural VOC emissions. Croplands, shrublands and other woodlands contribute 10-20% apiece. Isoprene emissions calcd. for temperate regions are as much as a factor of 5 higher than previous ests.
    12. 12
      Zhao, D.; Schmitt, S. H.; Wang, M.; Acir, I.-H.; Tillmann, R.; Tan, Z.; Novelli, A.; Fuchs, H.; Pullinen, I.; Wegener, R. Effects of NOx and SO2 on the Secondary Organic Aerosol Formation from Photooxidation of α-Pinene and Limonene. Atmospheric Chem. Phys. 2018, 18 (3), 1611– 1628,  DOI: 10.5194/acp-18-1611-2018
      12
      Effects of NOx and SO2 on the secondary organic aerosol formation from photooxidation of a-pinene and limonene
      Zhao, Defeng; Schmitt, Sebastian H.; Wang, Mingjin; Acir, Ismail-Hakki; Tillmann, Ralf; Tan, Zhaofeng; Novelli, Anna; Fuchs, Hendrik; Pullinen, Iida; Wegener, Robert; Rohrer, Franz; Wildt, Juergen; Kiendler-Scharr, Astrid; Wahner, Andreas; Mentel, Thomas F.
      Atmospheric Chemistry and Physics (2018), 18 (3), 1611-1628CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      Anthropogenic emissions such as NOx and SO2 influence the biogenic secondary org. aerosol (SOA) formation, but detailed mechanisms and effects are still elusive. We studied the effects of NOx and SO2 on the SOA formation from the photooxidn. of α-pinene and limonene at ambient relevant NOx and SO2 concns. (NOx: < 1 to 20 ppb, SO2: < 0.05 to 15 ppb). In these expts., monoterpene oxidn. was dominated by OH oxidn. We found that SO2 induced nucleation and enhanced SOA mass formation. NOx strongly suppressed not only new particle formation but also SOA mass yield. However, in the presence of SO2 which induced a high no. concn. of particles after oxidn. to H2SO4, the suppression of the mass yield of SOA by NOx was completely or partly compensated for. This indicates that the suppression of SOA yield by NOx was largely due to the suppressed new particle formation, leading to a lack of particle surface for the orgs. to condense on and thus a significant influence of vapor wall loss on SOA mass yield. By compensating for the suppressing effect on nucleation of NOx, SO2 also compensated for the suppressing effect on SOA yield. Aerosol mass spectrometer data show that increasing NOx enhanced nitrate formation. The majority of the nitrate was org. nitrate (57-77 %), even in low-NOx conditions (< ∼ 1 ppb). Org. nitrate contributed 7-26 % of total orgs. assuming a mol. wt. of 200 g mol-1. SOA from α-pinene photooxidn. at high NOx had a generally lower hydrogen to carbon ratio (H / C), compared to low NOx. The NOx dependence of the chem. compn. can be attributed to the NOx dependence of the branching ratio of the RO2 loss reactions, leading to a lower fraction of org. hydroperoxides and higher fractions of org. nitrates at high NOx. While NOx suppressed new particle formation and SOA mass formation, SO2 can compensate for such effects, and the combining effect of SO2 and NOx may have an important influence on SOA formation affected by interactions of biogenic volatile org. compds. (VOCs) with anthropogenic emissions.
    13. 13
      Schwantes, R. H.; Charan, S. M.; Bates, K. H.; Huang, Y.; Nguyen, T. B.; Mai, H.; Kong, W.; Flagan, R. C.; Seinfeld, J. H. Low-Volatility Compounds Contribute Significantly to Isoprene Secondary Organic Aerosol (SOA) under High-NOx Conditions. Atmospheric Chem. Phys. 2019, 19 (11), 7255– 7278,  DOI: 10.5194/acp-19-7255-2019
      13
      Low-volatility compounds contribute significantly to isoprene secondary organic aerosol (SOA) under high-NOx conditions
      Schwantes, Rebecca H.; Charan, Sophia M.; Bates, Kelvin H.; Huang, Yuanlong; Nguyen, Tran B.; Mai, Huajun; Kong, Weimeng; Flagan, Richard C.; Seinfeld, John H.
      Atmospheric Chemistry and Physics (2019), 19 (11), 7255-7278CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      Recent advances in our knowledge of the gas-phase oidation of isoprene, the impact of chamber walls on secondary org. aerosol (SOA) mass yields, and aerosol measurement anal. techniques warrant reevaluating SOA yields from isoprene. In particular, SOA from isoprene oidation under high-NOx conditions forms via two major pathways: (1) low-volatility nitrates and dinitrates (LV pathway) and (2) hydroymethyl-methyl-a-lactone (HMML) reaction on a surface or the condensed phase of particles to form 2-Me glyceric acid and its oligomers (2MGA pathway). These SOA prodn. pathways respond differently to reaction conditions. Past chamber expts. generated SOA with varying contributions from these two unique pathways, leading to results that are difficult to interpret. This study examines the SOA yields from these two pathways independently, which improves the interpretation of previous results and provides further understanding of the relevance of chamber SOA yields to the atm. and regional or global modeling. Results suggest that low-volatility nitrates and dinitrates produce significantly more aerosol than previously thought; the exptl. measured SOA mass yield from the LV pathway is ∼0.15. Sufficient seed surface area at the start of the reaction is needed to limit the effects of vapor wall losses of low-volatility compds. and accurately measure the complete SOA mass yield. Under dry conditions, substantial amts. of SOA are formed from HMML ring-opening reactions with inorg. ions and HMML org. oligomerization processes. However, the lactone org. oligomerization reactions are suppressed under more atmospherically relevant humidity levels, where hydration of the lactone is more competitive. This limits the SOA formation potential from the 2MGA pathway to HMML ring-opening reactions with water or inorg. ions under typical atm. conditions. The isoprene SOA mass yield from the LV pathway measured in this work is significantly higher than previous studies have reported, suggesting that low-volatility compds. such as org. nitrates and dinitrates may contribute to isoprene SOA under high-NOx conditions significantly more than previously thought and thus deserve continued study.
    14. 14
      Yan, C.; Nie, W.; Vogel, A. L.; Dada, L.; Lehtipalo, K.; Stolzenburg, D.; Wagner, R.; Rissanen, M. P.; Xiao, M.; Ahonen, L. Size-Dependent Influence of NOx on the Growth Rates of Organic Aerosol Particles. Sci. Adv. 2020, 6 (22), eaay4945,  DOI: 10.1126/sciadv.aay4945
      There is no corresponding record for this reference.
    15. 15
      Crounse, J. D.; Nielsen, L. B.; Jørgensen, S.; Kjaergaard, H. G.; Wennberg, P. O. Autoxidation of Organic Compounds in the Atmosphere. J. Phys. Chem. Lett. 2013, 4 (20), 3513– 3520,  DOI: 10.1021/jz4019207
      15
      Autoxidation of Organic Compounds in the Atmosphere
      Crounse, John D.; Nielsen, Lasse B.; Joergensen, Solvejg; Kjaergaard, Henrik G.; Wennberg, Paul O.
      Journal of Physical Chemistry Letters (2013), 4 (20), 3513-3520CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      A hypothesis that auto-oxidn. (inter- and intra-mol. H abstraction by peroxy radicals) plays an important role in the atm. oxidn. of org. compds., particularly org. matter assocd. with aerosols, is discussed. The rate of this process at room temp. was detd. in the lab. for a model compd., 3-pentanone. Ab-initio calcns. assessed H-shifts within a broader group of substituted org. compds. The rate of H abstraction by peroxy radicals was largely detd. by the thermochem. of nascent alkyl radicals; thus, it was highly affected by neighboring substituents. As a result, auto-oxidn. rates increased rapidly as O-contg. functional groups (carbonyl, hydroxy, hydroperoxy) are added to org. compds. This mechanism was consistent with formation of the multi-functional hydroperoxides and carbonyls often obsd. in atm. aerosol particles.
    16. 16
      Wennberg, P. O.; Bates, K. H.; Crounse, J. D.; Dodson, L. G.; McVay, R. C.; Mertens, L. A.; Nguyen, T. B.; Praske, E.; Schwantes, R. H.; Smarte, M. D. Gas-Phase Reactions of Isoprene and Its Major Oxidation Products. Chem. Rev. 2018, 118 (7), 3337– 3390,  DOI: 10.1021/acs.chemrev.7b00439
      16
      Gas-Phase Reactions of Isoprene and Its Major Oxidation Products
      Wennberg, Paul O.; Bates, Kelvin H.; Crounse, John D.; Dodson, Leah G.; McVay, Renee C.; Mertens, Laura A.; Nguyen, Tran B.; Praske, Eric; Schwantes, Rebecca H.; Smarte, Matthew D.; St Clair, Jason M.; Teng, Alexander P.; Zhang, Xuan; Seinfeld, John H.
      Chemical Reviews (Washington, DC, United States) (2018), 118 (7), 3337-3390CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. Isoprene carries approx. half of the flux of non-methane volatile org. carbon emitted to the atm. by the biosphere. Accurate representation of its oxidn. rate and products is essential for quantifying its influence on the abundance of the hydroxyl radical (OH), nitrogen oxide free radicals (NOx), ozone (O3), and, via the formation of highly oxygenated compds., aerosol. We present a review of recent lab. and theor. studies of the oxidn. pathways of isoprene initiated by addn. of OH, O3, the nitrate radical (NO3), and the chlorine atom. From this review, a recommendation for a nearly complete gas-phase oxidn. mechanism of isoprene and its major products is developed. The mechanism is compiled with the aims of providing an accurate representation of the flow of carbon while allowing quantification of the impact of isoprene emissions on HOx and NOx free radical concns. and of the yields of products known to be involved in condensed-phase processes. Finally, a simplified (reduced) mechanism is developed for use in chem. transport models that retains the essential chem. required to accurately simulate isoprene oxidn. under conditions where it occurs in the atm.-above forested regions remote from large NOx emissions.
    17. 17
      Bianchi, F.; Kurtén, T.; Riva, M.; Mohr, C.; Rissanen, M. P.; Roldin, P.; Berndt, T.; Crounse, J. D.; Wennberg, P. O.; Mentel, T. F. Highly Oxygenated Organic Molecules (HOM) from Gas-Phase Autoxidation Involving Peroxy Radicals: A Key Contributor to Atmospheric Aerosol. Chem. Rev. 2019, 119 (6), 3472– 3509,  DOI: 10.1021/acs.chemrev.8b00395
      17
      Highly Oxygenated Molecules (HOM) from Gas-Phase Autoxidation Involving Organic Peroxy Radicals: A Key Contributor to Atmospheric Aerosol
      Bianchi, Federico; Kurten, Theo; Riva, Matthieu; Mohr, Claudia; Rissanen, Matti P.; Roldin, Pontus; Berndt, Torsten; Crounse, John D.; Wennberg, Paul O.; Mentel, Thomas F.; Wildt, Jurgen; Junninen, Heikki; Jokinen, Tuija; Kulmala, Markku; Worsnop, Douglas R.; Thornton, Joel A.; Donahue, Neil; Kjaergaard, Henrik G.; Ehn, Mikael
      Chemical Reviews (Washington, DC, United States) (2019), 119 (6), 3472-3509CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review which defines highly oxygenated org. mols. (HOM) formed in the atm. via auto-oxidn. involving peroxy radicals arising from volatile org. compds. describing currently available techniques for their identification/quantification, followed by a summary of the current knowledge on their formation mechanisms and physicochem. properties, is given. Major aims are to provide a common frame for the currently quite fragmented literature on HOM studies and highlighting existing gaps, and suggesting directions for future HOM research. Topics discussed include: introduction; HOM background (defining key concepts, HOM in relation to other classification schemes, historical naming conventions); HOM detection (gas and particle phases, uncertainties and anal. challenges of HOM detection); HOM formation mechanisms (auto-oxidn. involving peroxy radical as HOM source, bimol. RO2 reactions, factors affecting HOM formation); HOM properties and atm. fate (physicochem. properties, removal mechanisms); HOM atm. observations and impact (ambient HOM observation, atm. impact); and summary and perspectives.
    18. 18
      Daellenbach, K. R.; Uzu, G.; Jiang, J.; Cassagnes, L.-E.; Leni, Z.; Vlachou, A.; Stefenelli, G.; Canonaco, F.; Weber, S.; Segers, A. Sources of Particulate-Matter Air Pollution and Its Oxidative Potential in Europe. Nature 2020, 587 (7834), 414– 419,  DOI: 10.1038/s41586-020-2902-8
      18
      Sources of particulate-matter air pollution and its oxidative potential in Europe
      Daellenbach, Kaspar R.; Uzu, Gaelle; Jiang, Jianhui; Cassagnes, Laure-Estelle; Leni, Zaira; Vlachou, Athanasia; Stefenelli, Giulia; Canonaco, Francesco; Weber, Samuel; Segers, Arjo; Kuenen, Jeroen J. P.; Schaap, Martijn; Favez, Olivier; Albinet, Alexandre; Aksoyoglu, Sebnem; Dommen, Josef; Baltensperger, Urs; Geiser, Marianne; El Haddad, Imad; Jaffrezo, Jean-Luc; Prevot, Andre S. H.
      Nature (London, United Kingdom) (2020), 587 (7834), 414-419CODEN: NATUAS; ISSN:0028-0836. (Nature Research)
      Abstr.: Particulate matter is a component of ambient air pollution that has been linked to millions of annual premature deaths globally1-3. Assessments of the chronic and acute effects of particulate matter on human health tend to be based on mass concn., with particle size and compn. also thought to play a part4. Oxidative potential has been suggested to be one of the many possible drivers of the acute health effects of particulate matter, but the link remains uncertain5-8. Studies investigating the particulate-matter components that manifest an oxidative activity have yielded conflicting results7. In consequence, there is still much to be learned about the sources of particulate matter that may control the oxidative potential concn.7. Here we use field observations and air-quality modeling to quantify the major primary and secondary sources of particulate matter and of oxidative potential in Europe. We find that secondary inorg. components, crustal material and secondary biogenic org. aerosols control the mass concn. of particulate matter. By contrast, oxidative potential concn. is assocd. mostly with anthropogenic sources, in particular with fine-mode secondary org. aerosols largely from residential biomass burning and coarse-mode metals from vehicular non-exhaust emissions. Our results suggest that mitigation strategies aimed at reducing the mass concns. of particulate matter alone may not reduce the oxidative potential concn. If the oxidative potential can be linked to major health impacts, it may be more effective to control specific sources of particulate matter rather than overall particulate mass.
    19. 19
      Xiong, Q.; Yu, H.; Wang, R.; Wei, J.; Verma, V. Rethinking Dithiothreitol-Based Particulate Matter Oxidative Potential: Measuring Dithiothreitol Consumption versus Reactive Oxygen Species Generation. Environ. Sci. Technol. 2017, 51 (11), 6507– 6514,  DOI: 10.1021/acs.est.7b01272
      19
      Rethinking Dithiothreitol-Based Particulate Matter Oxidative Potential: Measuring Dithiothreitol Consumption versus Reactive Oxygen Species Generation
      Xiong, Qianshan; Yu, Haoran; Wang, Runran; Wei, Jinlai; Verma, Vishal
      Environmental Science & Technology (2017), 51 (11), 6507-6514CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      We measured the rate of generation of reactive oxygen species (ROS) [hydroxyl radicals (•OH) and hydrogen peroxide (H2O2)] catalyzed by ambient particulate matter (PM) in the dithiothreitol (DTT) assay. To understand the mechanism of ROS generation, we tested several redox-active substances, such as 9,10-phenanthrenequinone (PQ), 5-hydroxy-1,4-naphthoquinone (5H-1,4NQ), 1,2-naphthoquinone (1,2-NQ), 1,4-naphthoquinone (1,4-NQ), copper(II), manganese(II), and iron (II and III). Both pure compds. and their mixts. show different patterns in DTT oxidn. vs. ROS generation. The quinones, known to oxidize DTT in the efficiency order of PQ > 5H-1,4NQ > 1,2-NQ > 1,4-NQ, show a different efficiency order (5H-1,4NQ > 1,2-NQ ≈ PQ > 1,4-NQ) in the ROS generation. Cu(II), a dominant metal in DTT oxidn., contributes almost negligibly to the ROS generation. Fe is mostly inactive in DTT oxidn., but shows synergistic effect in •OH formation in the presence of other quinones (mixt./sum > 1.5). Ten ambient PM samples collected from an urban site were analyzed, and although DTT oxidn. was significantly correlated with H2O2 generation (Pearson's r = 0.91), no correlation was obsd. between DTT oxidn. and •OH formation. Our results show that measuring both DTT consumption and ROS generation in the DTT assay is important to incorporate the synergistic contribution from different aerosol components and to provide a more inclusive picture of the ROS activity of ambient PM.
    20. 20
      Fang, T.; Lakey, P. S. J.; Weber, R. J.; Shiraiwa, M. Oxidative Potential of Particulate Matter and Generation of Reactive Oxygen Species in Epithelial Lining Fluid. Environ. Sci. Technol. 2019, 53 (21), 12784– 12792,  DOI: 10.1021/acs.est.9b03823
      20
      Oxidative Potential of Particulate Matter and Generation of Reactive Oxygen Species in Epithelial Lining Fluid
      Fang, Ting; Lakey, Pascale S. J.; Weber, Rodney J.; Shiraiwa, Manabu
      Environmental Science & Technology (2019), 53 (21), 12784-12792CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Reactive oxygen species (ROS) play a central role in adverse health effects of atm. particulate matter (PM). Respiratory deposition can lead to ROS formation in epithelial lining fluid due to redox reactions of PM components with lung antioxidants. Since direct ROS quantification is challenging, PM oxidative potential is more commonly measured using antioxidant surrogates, including dithiothreitol (DTT) and ascorbic acid, assuming that surrogate decay corresponds with ROS formation. This assumption has not been validated and the lack of ROS quantification in the respiratory tract causes major limitations in evaluating PM impacts on oxidative stress. By combining field measurements of size-segregated chem. compn., a human respiratory tract model, and kinetic modeling, the authors quantified prodn. rates and concns. of different types of ROS in different regions of the epithelial lining fluid by considering particle size-dependent respiratory deposition. The extra-thoracic region had higher ROS concns. vs. bronchial and alveolar regions. While H2O2 and O2- prodn. is governed by Fe and Cu ions, OH- are mainly generated by org. compds. and metal ions Fenton-like reactions. In winter affected by biomass burning, model comparisons suggested humic-like substances contribute substantially to ROS formation. PM oxidative potential was detd. to be a good indicator of chem. H2O2 and O2- prodn., but did not represent OH- generation. Results provided rationale and limitations for using oxidative potential as an indicator for PM toxicity in epidemiol. and toxicol. studies.
    21. 21
      Wei, J.; Fang, T.; Wong, C.; Lakey, P. S. J.; Nizkorodov, S. A.; Shiraiwa, M. Superoxide Formation from Aqueous Reactions of Biogenic Secondary Organic Aerosols. Environ. Sci. Technol. 2021, 55 (1), 260– 270,  DOI: 10.1021/acs.est.0c07789
      21
      Superoxide formation from aqueous reactions of biogenic secondary organic aerosols
      Wei, Jinlai; Fang, Ting; Wong, Cynthia; Lakey, Pascale S. J.; Nizkorodov, Sergey A.; Shiraiwa, Manabu
      Environmental Science & Technology (2021), 55 (1), 260-270CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Reactive oxygen species (ROS) play a central role in aq.-phase processing and health effects of atm. aerosols. Although hydroxyl radical (•OH) and hydrogen peroxide (H2O2) are regarded as major oxidants assocd. with secondary org. aerosols (SOA), the kinetics and reaction mechanisms of superoxide (O2•-) formation are rarely quantified and poorly understood. Here, we demonstrate a dominant formation of O2•- with molar yields of 0.01-0.03% from aq. reactions of biogenic SOA generated by •OH photooxidn. of isoprene, β-pinene, α-terpineol, and D-limonene. The temporal evolution of •OH and O2•- formation is elucidated by kinetic modeling with a cascade of aq. reactions including the decompn. of org. hydroperoxides, •OH oxidn. of primary or secondary alcs., and unimol. decompn. of α-hydroxyperoxyl radicals. Relative yields of various types of ROS reflect a relative abundance of org. hydroperoxides and alcs. contained in SOA. These findings and mechanistic understanding have important implications on the atm. fate of SOA and particle-phase reactions of highly oxygenated org. mols. as well as oxidative stress upon respiratory deposition.
    22. 22
      Tong, H.; Arangio, A. M.; Lakey, P. S. J.; Berkemeier, T.; Liu, F.; Kampf, C. J.; Brune, W. H.; Pöschl, U.; Shiraiwa, M. Hydroxyl Radicals from Secondary Organic Aerosol Decomposition in Water. Atmospheric Chem. Phys. 2016, 16 (3), 1761– 1771,  DOI: 10.5194/acp-16-1761-2016
      22
      Hydroxyl radicals from secondary organic aerosol decomposition in water
      Tong, Haijie; Arangio, Andrea M.; Lakey, Pascale S. J.; Berkemeier, Thomas; Liu, Fobang; Kampf, Christopher J.; Brune, William H.; Poeschl, Ulrich; Shiraiwa, Manabu
      Atmospheric Chemistry and Physics (2016), 16 (3), 1761-1771CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      We found that ambient and lab.-generated secondary org. aerosols (SOA) form substantial amts. of OH radicals upon interaction with liq. water, which can be explained by the decompn. of org. hydroperoxides. The molar OH yield from SOA formed by ozonolysis of terpenes (α-pinene, β-pinene, limonene) is ∼0.1% upon extn. with pure water and increases to ∼1.5% in the presence of Fe2+ ions due to Fenton-like reactions. Upon extn. of SOA samples from OH photooxidn. of isoprene, we also detected OH yields of around ∼0.1 %, which increases upon addn. of Fe2+. Our findings imply that the chem. reactivity and aging of SOA particles is strongly enhanced upon interaction with water and iron. In cloud droplets under dark conditions, SOA decompn. can compete with the classical H2O2 Fenton reaction as the source of OH radicals. Also in the human respiratory tract, the inhalation and deposition of SOA particles may lead to a substantial release of OH radicals, which may contribute to oxidative stress and play an important role in the adverse health effects of atm. aerosols.
    23. 23
      Shiraiwa, M.; Selzle, K.; Pöschl, U. Hazardous Components and Health Effects of Atmospheric Aerosol Particles: Reactive Oxygen Species, Soot, Polycyclic Aromatic Compounds and Allergenic Proteins. Free Radic. Res. 2012, 46 (8), 927– 939,  DOI: 10.3109/10715762.2012.663084
      23
      Hazardous components and health effects of atmospheric aerosol particles: reactive oxygen species, soot, polycyclic aromatic compounds and allergenic proteins
      Shiraiwa, Manabu; Selzle, Kathrin; Poeschl, Ulrich
      Free Radical Research (2012), 46 (8), 927-939CODEN: FRARER; ISSN:1029-2470. (Informa Healthcare)
      A review. This review outlines recent advances in the investigation of the chem. properties, mol. interactions and health effects of hazardous compds. in atm. aerosols, in particular reactive oxygen species (ROS), soot, polycyclic arom. compds. (PACs) and allergenic proteins. Epidemiol. studies show correlations between air particulate matter and adverse health effects of air pollution including allergy, asthma, cardiovascular and respiratory diseases, but the causative relations and mechanisms of interaction on the mol. level are still unclear. ROS generated by photochem. and heterogeneous reactions in the atm. seem to play a key role in aerosol health effects and provide a direct link between atm. and physiol. multiphase processes. Soot and PACs can trigger formation of ROS in vivo, leading to inflammation and cellular damage. PACs as well as allergenic proteins are efficiently oxygenated and nitrated upon exposure to ozone and nitrogen dioxide, which leads to an enhancement of their toxicity and allergenicity.
    24. 24
      Lakey, P. S. J.; Berkemeier, T.; Tong, H.; Arangio, A. M.; Lucas, K.; Pöschl, U.; Shiraiwa, M. Chemical Exposure-Response Relationship between Air Pollutants and Reactive Oxygen Species in the Human Respiratory Tract. Sci. Rep. 2016, 6 (1), 32916,  DOI: 10.1038/srep32916
      24
      Chemical exposure-response relationship between air pollutants and reactive oxygen species in the human respiratory tract
      Lakey, Pascale S. J.; Berkemeier, Thomas; Tong, Haijie; Arangio, Andrea M.; Lucas, Kurt; Poeschl, Ulrich; Shiraiwa, Manabu
      Scientific Reports (2016), 6 (), 32916CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
      Air pollution can cause oxidative stress and adverse health effects such as asthma and other respiratory diseases, but the underlying chem. processes are not well characterized. Here we present chem. exposure-response relations between ambient concns. of air pollutants and the prodn. rates and concns. of reactive oxygen species (ROS) in the epithelial lining fluid (ELF) of the human respiratory tract. In highly polluted environments, fine particulate matter (PM2.5) contg. redox-active transition metals, quinones, and secondary org. aerosols can increase ROS concns. in the ELF to levels characteristic for respiratory diseases. Ambient ozone readily sats. the ELF and can enhance oxidative stress by depleting antioxidants and surfactants. Chem. exposure-response relations provide a quant. basis for assessing the relative importance of specific air pollutants in different regions of the world, showing that aerosol-induced epithelial ROS levels in polluted megacity air can be several orders of magnitude higher than in pristine rainforest air.
    25. 25
      Li, N.; Xia, T.; Nel, A. E. The Role of Oxidative Stress in Ambient Particulate Matter-Induced Lung Diseases and Its Implications in the Toxicity of Engineered Nanoparticles. Free Radic. Biol. Med. 2008, 44 (9), 1689– 1699,  DOI: 10.1016/j.freeradbiomed.2008.01.028
      25
      The role of oxidative stress in ambient particulate matter-induced lung diseases and its implications in the toxicity of engineered nanoparticles
      Li, Ning; Xia, Tian; Nel, Andre E.
      Free Radical Biology & Medicine (2008), 44 (9), 1689-1699CODEN: FRBMEH; ISSN:0891-5849. (Elsevier)
      A review. Ambient particulate matter (PM) is an environmental factor that has been assocd. with increased respiratory morbidity and mortality. The major effect of ambient PM on the pulmonary system is the exacerbation of inflammation, esp. in susceptible people. One of the mechanisms by which ambient PM exerts its proinflammatory effects is the generation of oxidative stress by its chem. compds. and metals. Cellular responses to PM-induced oxidative stress include activation of antioxidant defense, inflammation, and toxicity. The proinflammatory effect of PM in the lung is characterized by increased cytokine/chemokine prodn. and adhesion mol. expression. Moreover, there is evidence that ambient PM can act as an adjuvant for allergic sensitization, which raises the possibility that long-term PM exposure may lead to increased prevalence of asthma. In addn. to ambient PM, rapid expansion of nanotechnol. has introduced the potential that engineered nanoparticles (NP) may also become airborne and may contribute to pulmonary diseases by novel mechanisms that could include oxidant injury. Currently, little is known about the potential adverse health effects of these particles. In this communication, the mechanisms by which particulate pollutants, including ambient PM and engineered NP, exert their adverse effects through the generation of oxidative stress and the impacts of oxidant injury in the respiratory tract will be reviewed. The importance of cellular antioxidant and detoxification pathways in protecting against particle-induced lung damage will also be discussed.
    26. 26
      Mazzoli-Rocha, F.; Fernandes, S.; Einicker-Lamas, M.; Zin, W. A. Roles of Oxidative Stress in Signaling and Inflammation Induced by Particulate Matter. Cell Biol. Toxicol. 2010, 26 (5), 481– 498,  DOI: 10.1007/s10565-010-9158-2
      26
      Roles of oxidative stress in signaling and inflammation induced by particulate matter
      Mazzoli-Rocha, Flavia; Fernandes, Silviane; Einicker-Lamas, Marcelo; Zin, Walter Araujo
      Cell Biology and Toxicology (2010), 26 (5), 481-498CODEN: CBTOE2; ISSN:0742-2091. (Springer)
      A review. This review reports the role of oxidative stress in impairing the function of lung exposed to particulate matter (PM). PM constitutes a heterogeneous mixt. of various types of particles, many of which are likely to be involved in oxidative stress induction and respiratory diseases. Probably, the ability of PM to cause oxidative stress underlies the assocn. between increased exposure to PM and exacerbations of lung disease. Mostly because of their large surface area, ultrafine particles have been shown to cause oxidative stress and proinflammatory effects in different in vivo and in vitro studies. Particle components and surface area may act synergistically inducing lung inflammation. In this vein, reactive oxygen species elicited upon PM exposure have been shown to activate a no. of redox-responsive signaling pathways and Ca2+ influx in lung target cells that are involved in the expression of genes that modulate relevant responses to lung inflammation and disease.
    27. 27
      Gehling, W.; Dellinger, B. Environmentally Persistent Free Radicals and Their Lifetimes in PM2.5. Environ. Sci. Technol. 2013, 47 (15), 8172– 8178,  DOI: 10.1021/es401767m
      27
      Environmentally Persistent Free Radicals and Their Lifetimes in PM2.5
      Gehling, William; Dellinger, Barry
      Environmental Science & Technology (2013), 47 (15), 8172-8178CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      For the first time, an expansive study into the concn. and extended decay behavior of environmentally persistent free radicals in PM2.5 was performed. Results from this study revealed three types of radical decay-a fast decay, slow decay, and no decay-following one of four decay patterns: a relatively fast decay exhibiting a 1/e lifetime of 1-21 days accompanied by a slow decay with a 1/e lifetime of 21-5028 days (47% of samples); a single slow decay including a 1/e lifetime of 4-2083 days (24% of samples); no decay (18% of samples); and a relatively fast decay displaying an av. 1/e lifetime of 0.25-21 days followed by no decay (11% of samples). Phenol correlated well with the initial radical concn. and fast decay rate. Other correlations for common atm. pollutants (ozone, NOx, SO2, etc.) as well as meteorol. conditions suggested photochem. processes impact the initial radical concn. and fast decay rate. The radical signal in PM2.5 was remarkably similar to semiquinones in cigarette smoke. Accordingly, radicals inhaled from PM2.5 were related to the radicals inhaled from smoking cigarettes, expressed as the no. of equiv. cigarettes smoked. This calcd. to 0.4-0.9 cigarettes per day for nonextreme air quality in the United States.
    28. 28
      Chowdhury, P. H.; He, Q.; Carmieli, R.; Li, C.; Rudich, Y.; Pardo, M. Connecting the Oxidative Potential of Secondary Organic Aerosols with Reactive Oxygen Species in Exposed Lung Cells. Environ. Sci. Technol. 2019, 53 (23), 13949– 13958,  DOI: 10.1021/acs.est.9b04449
      28
      Connecting the Oxidative Potential of Secondary Organic Aerosols with Reactive Oxygen Species in Exposed Lung Cells
      Chowdhury, Pratiti Home; He, Quanfu; Carmieli, Raanan; Li, Chunlin; Rudich, Yinon; Pardo, Michal
      Environmental Science & Technology (2019), 53 (23), 13949-13958CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      It has been hypothesized that the cytotoxicity of secondary org. aerosols (SOA) is mediated through the formation of reactive oxygen species (ROS) in the exposed cells. Here, lung epithelial cells (A549) residing at the air-liq. interface were exposed to proxies of anthropogenic and biogenic SOA that were photochem. aged under varying nitrogen oxide (NOx) concns. in an oxidn. flow reactor (OFR). The total org. peroxides and ROS radical content in the SOA were quantified by the iodometric-spectrophotometric method and by continuous-wave ESR (CW-EPR). The effect of the exposure was evaluated by measuring cell viability and cellular ROS prodn. following the exposure. The results demonstrate that SOA that aged in the absence of NOx contained more ROS than fresh SOA and were more toxic towards the cells, while varying NOx conditions had no significant influence on levels of ROS content in fresh SOA and their toxicity. Anal. of ROS in the exposed cells using flow cytometry showed a similar trend with the total ROS content in the SOA. This study provides a first and direct observation of such assocn.
    29. 29
      Tong, H.; Lakey, P. S. J.; Arangio, A. M.; Socorro, J.; Shen, F.; Lucas, K.; Brune, W. H.; Pöschl, U.; Shiraiwa, M. Reactive Oxygen Species Formed by Secondary Organic Aerosols in Water and Surrogate Lung Fluid. Environ. Sci. Technol. 2018, 52 (20), 11642– 11651,  DOI: 10.1021/acs.est.8b03695
      29
      Reactive Oxygen Species Formed by Secondary Organic Aerosols in Water and Surrogate Lung Fluid
      Tong, Haijie; Lakey, Pascale S. J.; Arangio, Andrea M.; Socorro, Joanna; Shen, Fangxia; Lucas, Kurt; Brune, William H.; Poeschl, Ulrich; Shiraiwa, Manabu
      Environmental Science & Technology (2018), 52 (20), 11642-11651CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Reactive O species (ROS) play a central role in the adverse health effects of air pollutants. Respiratory deposition of fine air particulate matter can lead to ROS formation in epithelial lining fluid, potentially causing oxidative stress and inflammation. Secondary org. aerosols (SOA) account for a large fraction of fine particulate matter, but their role in adverse health effects is unclear. This work quantified and compared ROS yields and oxidative potential of isoprene, β-pinene, and naphthalene SOA in water and surrogate lung fluid (SLF). In pure water, isoprene and β-pinene SOA produced mainly OH- and org. radicals; naphthalene SOA produced mainly H2O2 and O2-. Total molar ROS yields of isoprene and β-pinene SOA were 11.8 and 8.2% in water and decreased to 8.5 and 5.2% in SLF, resp., attributed to ROS removal by lung antioxidants. A pos. correlation between total peroxide concn. and ROS yield suggested org. (hydro)peroxides may play an important role in ROS formation from biogenic SOA. Total molar ROS yield of naphthalene SOA was 1.7% in water and increased to 11.3% in SLF. This strong increase was likely due to redox reaction cycles involving environmentally persistent free radicals or semiquinones, antioxidants, and O2, which may promote H2O2 formation and adverse health effects of anthropogenic SOA from arom. precursors.
    30. 30
      Vejerano, E. P.; Rao, G.; Khachatryan, L.; Cormier, S. A.; Lomnicki, S. Environmentally Persistent Free Radicals: Insights on a New Class of Pollutants. Environ. Sci. Technol. 2018, 52 (5), 2468– 2481,  DOI: 10.1021/acs.est.7b04439
      30
      Environmentally Persistent Free Radicals: Insights on a New Class of Pollutants
      Vejerano, Eric P.; Rao, Guiying; Khachatryan, Lavrent; Cormier, Stephania A.; Lomnicki, Slawo
      Environmental Science & Technology (2018), 52 (5), 2468-2481CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Environmentally persistent free radicals, EPFRs, exist in significant concn. in atm. particulate matter (PM). EPFRs are primarily emitted from combustion and thermal processing of org. materials, in which the org. combustion byproducts interact with transition metal-contg. particles to form a free radical-particle pollutant. While the existence of persistent free radicals in combustion has been known for over half-a-century, only recently that their presence in environmental matrixes and health effects have started significant research, but still in its infancy. Most of the exptl. studies conducted to understand the origin and nature of EPFRs have focused primarily on nanoparticles that are supported on a larger micrometer-sized particle that mimics incidental nanoparticles formed during combustion. Less is known on the extent by which EPFRs may form on engineered nanomaterials (ENMs) during combustion or thermal treatment. In this crit. and timely review, we summarize important findings on EPFRs and discuss their potential to form on pristine ENMs as a new research direction. ENMs may form EPFRs that may differ in type and concn. compared to nanoparticles that are supported on larger particles. The lack of basic data and fundamental knowledge about the interaction of combustion byproducts with ENMs under high-temp. and oxidative conditions present an unknown environmental and health burden. Studying the extent of ENMs on catalyzing EPFRs is important to address the hazards of atm. PM fully from these emerging environmental contaminants.
    31. 31
      Gehling, W.; Khachatryan, L.; Dellinger, B. Hydroxyl Radical Generation from Environmentally Persistent Free Radicals (EPFRs) in PM2.5. Environ. Sci. Technol. 2014, 48 (8), 4266– 4272,  DOI: 10.1021/es401770y
      31
      Hydroxyl Radical Generation from Environmentally Persistent Free Radicals (EPFRs) in PM2.5
      Gehling, William; Khachatryan, Lavrent; Dellinger, Barry
      Environmental Science & Technology (2014), 48 (8), 4266-4272CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Hydroxyl radicals generated from an aq. suspension of ambient PM2.5 and detected using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) in a spin trap in conjunction with ESR spectroscopy is discussed. Study results suggested the importance of environmentally persistent free radicals (EPFR) in PM2.5 to generate significant OH- concns. without adding H2O2. Particles for which EPFR were allowed to decay over time induced less OH-; also, higher particle concns. produced more OH-. Some samples did not alter OH- generation when the soln. was purged with air. This was ascribed to internal vs. external surface-assocd. EPFR.
    32. 32
      Kumagai, Y.; Koide, S.; Taguchi, K.; Endo, A.; Nakai, Y.; Yoshikawa, T.; Shimojo, N. Oxidation of Proximal Protein Sulfhydryls by Phenanthraquinone, a Component of Diesel Exhaust Particles. Chem. Res. Toxicol. 2002, 15 (4), 483– 489,  DOI: 10.1021/tx0100993
      32
      Oxidation of Proximal Protein Sulfhydryls by Phenanthraquinone, a Component of Diesel Exhaust Particles
      Kumagai, Yoshito; Koide, Sachie; Taguchi, Keiko; Endo, Akiko; Nakai, Yumi; Yoshikawa, Toshikazu; Shimojo, Nobuhiro
      Chemical Research in Toxicology (2002), 15 (4), 483-489CODEN: CRTOEC; ISSN:0893-228X. (American Chemical Society)
      Diesel exhaust particles (DEP) contain quinones that are capable of catalyzing the generation of reactive oxygen species in biol. systems, resulting in induction of oxidative stress. In the present study, we explored sulfhydryl oxidn. by phenanthraquinone, a component of DEP, using thiol compds. and protein prepns. Phenanthraquinone reacted readily with dithiol compds. such as dithiothreitol (DTT), 2,3-dimercapto-1-propanol (BAL), and 2,3-dimercapto-1-propanesulfonic acid (DMPS), resulting in modification of the thiol groups, whereas minimal reactivities of this quinone with monothiol compds. such as GSH, 2-mercaptoethanol, and N-acetyl-L-cysteine were seen. The modification of DTT dithiol caused by phenanthraquinone proceeded under anaerobic conditions but was accelerated by mol. oxygen. Phenanthraquinone was also capable of modifying thiol groups in pulmonary microsomes from rats and total membrane prepn. isolated from bovine aortic endothelial cells (BAEC), but not bovine serum albumin (BSA), which has a Cys34 as a reactive monothiol group. A comparison of the thiol alkylating agent N-ethylmaleimide (NEM) with that of phenanthraquinone indicates that the two mechanisms of thiol modification are distinct. Studies revealed that thiyl radical intermediates and reactive oxygen species were generated during interaction of phenanthraquinone with DTT. From these findings, it is suggested that phenanthraquinone-mediated destruction of protein sulfhydryls appears to involve the oxidn. of presumably proximal thiols and the redn. of mol. oxygen.
    33. 33
      Arangio, A. M.; Tong, H.; Socorro, J.; Pöschl, U.; Shiraiwa, M. Quantification of Environmentally Persistent Free Radicals and Reactiveoxygen Species in Atmospheric Aerosol Particles. Atmospheric Chem. Phys. 2016, 16 (20), 13105– 13119,  DOI: 10.5194/acp-16-13105-2016
      33
      Quantification of environmentally persistent free radicals and reactive oxygen species in atmospheric aerosol particles
      Arangio, Andrea M.; Tong, Haijie; Socorro, Joanna; Poeschl, Ulrich; Shiraiwa, Manabu
      Atmospheric Chemistry and Physics (2016), 16 (20), 13105-13119CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      Fine particulate matter plays a central role in the adverse health effects of air pollution. Inhalation and deposition of aerosol particles in the respiratory tract can lead to the release of reactive oxygen species (ROS), which may cause oxidative stress. In this study, we have detected and quantified a wide range of particle-assocd. radicals using ESR (EPR) spectroscopy. Ambient particle samples were collected using a cascade impactor at a semi-urban site in central Europe, Mainz, Germany, in May-June 2015. Concns. of environmentally persistent free radicals (EPFR), most likely semiquinone radicals, were found to be in the range of (1-7) × 1011 spins μg-1 for particles in the accumulation mode, whereas coarse particles with a diam. larger than 1 μm did not contain substantial amts. of EPFR. Using a spin trapping technique followed by deconvolution of EPR spectra, we have also characterized and quantified ROS, including OH, superoxide (O-2) and formed upon extn. of the particle samples in water. Total ROS amts. of (0.1-3) × 1011 spins μg-1 were released by submicron particle samples and the relative contributions of OH, O-2, C-centered and O-centered org. radicals were ∼11-31, ∼2-8, ∼41-72 and ∼0-25 %, resp., depending on particle sizes. OH was the dominant species for coarse particles. Based on comparisons of the EPR spectra of ambient particulate matter with those of mixts. of org. hydroperoxides, quinones and iron ions followed by chem. anal. using liq. chromatog. mass spectrometry (LC-MS), we suggest that the particle-assocd. ROS were formed by decompn. of org. hydroperoxides interacting with transition metal ions and quinones contained in atm. humic-like substances.
    34. 34
      Chen, Q.; Wang, M.; Wang, Y.; Zhang, L.; Xue, J.; Sun, H.; Mu, Z. Rapid Determination of Environmentally Persistent Free Radicals (EPFRs) in Atmospheric Particles with a Quartz Sheet-Based Approach Using Electron Paramagnetic Resonance (EPR) Spectroscopy. Atmos. Environ. 2018, 184, 140– 145,  DOI: 10.1016/j.atmosenv.2018.04.046
      34
      Rapid determination of environmentally persistent free radicals (EPFRs) in atmospheric particles with a quartz sheet-based approach using electron paramagnetic resonance (EPR) spectroscopy
      Chen, Qingcai; Wang, Mamin; Wang, Yuqin; Zhang, Lixin; Xue, Jian; Sun, Haoyao; Mu, Zhen
      Atmospheric Environment (2018), 184 (), 140-145CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
      Environmentally persistent free radicals (EPFRs) are present within atm. fine particles, and they are assumed to be a potential factor responsible for human pneumonia and lung cancer. This study presents a new method for the rapid quantification of EPFRs in atm. particles with a quartz sheet-based approach using ESR (EPR) spectroscopy. The three-dimensional distributions of the relative response factors in a cavity resonator were simulated and utilized for an accurate quant. detn. of EPFRs in samples. Comparisons between the proposed method and conventional quant. methods were also performed to illustrate the advantages of the proposed method. The results suggest that the reproducibility and accuracy of the proposed method are superior to those of the quartz tube-based method. Although the solvent extn. method is capable of extg. specific EPFR species, the developed method can be used to det. the total EPFR content; moreover, the anal. process of the proposed approach is substantially quicker than that of the solvent extn. method. The proposed method has been applied in this study to det. the EPFRs in ambient PM2.5 samples collected over Xi'an, the results of which will be useful for extensive research on the sources, concns., and phys.-chem. characteristics of EPFRs in the atm.
    35. 35
      Borrowman, C. K.; Zhou, S.; Burrow, T. E.; Abbatt, J. P. D. Formation of Environmentally Persistent Free Radicals from the Heterogeneous Reaction of Ozone and Polycyclic Aromatic Compounds. Phys. Chem. Chem. Phys. 2016, 18 (1), 205– 212,  DOI: 10.1039/C5CP05606C
      35
      Formation of environmentally persistent free radicals from the heterogeneous reaction of ozone and polycyclic aromatic compounds
      Borrowman, Cuyler K.; Zhou, Shouming; Burrow, Timothy E.; Abbatt, Jonathan P. D.
      Physical Chemistry Chemical Physics (2016), 18 (1), 205-212CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      In the 1980s long-lived radical species were identified in cigarette tar. Since then, environmentally persistent free radicals (EPFR) have been obsd. in ambient particulate matter, and have been generated by an entrained in internal combustion engine particulate matter. For the first time, EPFR in-situ formation and decay was measured by the heterogeneous reaction of O3 with several polycyclic arom. compds. (PAH). Solid anthracene, pyrene, 1,4-naphthoquinone, and 9,10-anthraquinone (AQ) were reacted with gaseous O3 in a flow system installed in the active cavity of an ESR spectrometer, and radical formation was measured on a tens-of-minutes time-scale at ambient O3 concns. down to 30 ppb. For most substrates, net radical prodn. was initially rapid, slowed at intermediate times, and was followed by a slow decay. For oxidized, solid BAP, the radical signal persisted for many days in the absence of O3. To evaluate the effect of substrate phase, solid PAH were also dissolved in squalane, an org. oil inert to O3, which yielded a much higher max. radical concn. and faster radical decay when exposed to O3. With higher mobility, reactants were apparently able to more easily diffuse and react, yielding higher radical concns. EPR spectra exhibited 3 radicals types, 2 of which were assigned to semiquinone species and 1 to a PAH-derived, C-centered radical. Although the system used PAH concns. not typically obsd. in the environment, the amts. of radicals formed (on the order of 1018 radicals/g), was comparable to that obsd. in ambient particulate matter.
    36. 36
      Villamena, F. A.; Zweier, J. L. Detection of Reactive Oxygen and Nitrogen Species by EPR Spin Trapping. Antioxid. Redox Signal. 2004, 6 (3), 619– 629,  DOI: 10.1089/152308604773934387
      36
      Detection of reactive oxygen and nitrogen species by EPR spin trapping
      Villamena Frederick A; Zweier Jay L
      Antioxidants & redox signaling (2004), 6 (3), 619-29 ISSN:1523-0864.
      Electron paramagnetic resonance spin trapping has become an indispensable tool for the specific detection of reactive oxygen free radicals in biological systems. In this review we describe some of the advantages as well as some experimental considerations of this technique and how it can be applied to biological systems to measure oxidative stress.
    37. 37
      Klodt, A. L. ICARUS Experiment Set: APIN and NAP SOA generation for reactive oxygen species measurements, ICARUS [data set], available at: https://icarus.ucdavis.edu/experimentset/249 (accessed 2022-06-22).
      There is no corresponding record for this reference.
    38. 38
      Hinks, M. L.; Montoya-Aguilera, J.; Ellison, L.; Lin, P.; Laskin, A.; Laskin, J.; Shiraiwa, M.; Dabdub, D.; Nizkorodov, S. A. Effect of Relative Humidity on the Composition of Secondary Organic Aerosol from the Oxidation of Toluene. Atmospheric Chem. Phys. 2018, 18 (3), 1643– 1652,  DOI: 10.5194/acp-18-1643-2018
      38
      Effect of relative humidity on the composition of secondary organic aerosol from the oxidation of toluene
      Hinks, Mallory L.; Montoya-Aguilera, Julia; Ellison, Lucas; Lin, Peng; Laskin, Alexander; Laskin, Julia; Shiraiwa, Manabu; Dabdub, Donald; Nizkorodov, Sergey A.
      Atmospheric Chemistry and Physics (2018), 18 (3), 1643-1652CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      The effect of relative humidity (RH) on the chem. compn. of secondary org. aerosol (SOA) formed from low-NOx toluene oxidn. in the absence of seed particles was investigated. SOA samples were prepd. in an aerosol smog chamber at < 2% RH and 75% RH, collected on Teflon filters, and analyzed with nanospray desorption electrospray ionization high-resoln. mass spectrometry (nano-DESI-HRMS). Measurements revealed a significant redn. in the fraction of oligomers present in the SOA generated at 75% RH compared to SOA generated under dry conditions. In a sep. set of expts., the particle mass concns. were measured with a scanning mobility particle sizer (SMPS) at RHs ranging from < 2 to 90%. It was found that the particle mass loading decreased by nearly an order of magnitude when RH increased from < 2 to 75-90% for low-NOx toluene SOA. The volatility distributions of the SOA compds., estd. from the distribution of mol. formulas using the "mol. corridor" approach, confirmed that low-NOx toluene SOA became more volatile on av. under high-RH conditions. In contrast, the effect of RH on SOA mass loading was found to be much smaller for high-NOx toluene SOA. The obsd. increase in the oligomer fraction and particle mass loading under dry conditions were attributed to the enhancement of condensation reactions, which produce water and oligomers from smaller compds. in low-NOx toluene SOA. The redn. in the fraction of oligomeric compds. under humid conditions is predicted to partly counteract the previously obsd. enhancement in the toluene SOA yield driven by the aerosol liq. water chem. in deliquesced inorg. seed particles.
    39. 39
      Saleh, R.; Donahue, N. M.; Robinson, A. L. Time Scales for Gas-Particle Partitioning Equilibration of Secondary Organic Aerosol Formed from Alpha-Pinene Ozonolysis. Environ. Sci. Technol. 2013, 47 (11), 5588– 5594,  DOI: 10.1021/es400078d
      39
      Time Scales for Gas-Particle Partitioning Equilibration of Secondary Organic Aerosol Formed from Alpha-Pinene Ozonolysis
      Saleh, Rawad; Donahue, Neil M.; Robinson, Allen L.
      Environmental Science & Technology (2013), 47 (11), 5588-5594CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Most chem. transport models assume instantaneous equil. to represent gas-particle partitioning of semivolatile org. aerosol. This approach has been challenged by recent studies suggesting that secondary org. aerosol (SOA) cannot reach equil. within atm. time scales. The emergent hypothesis is that gas-particle partitioning rates are limited by diffusion within the condensed phase, which probably is glassy. Here, we study the equilibration time scales of SOA formed from α-pinene ozonolysis by measuring the dynamic response to a modest step-change in temp. Upon heating, equil. is disturbed, and the particles evap. to restore equil. at the new temp., which is attained when evapn. ceases. The SOA was formed at 10° and then heated to near room temp. (30°) so that the phase state (viscosity) of the condensed-phase after heating is similar to how it would be in the atm. Expts. were performed in both a thermodenuder, with SOA loading of 350 μg/m3, and in a smog chamber, with SOA loading of 2-12 μg/m3. Both expts. show, contrary to previous findings, that the SOA achieves equil. with dynamic responses consistent with a mass accommodation coeff. of order 0.1. For typical atm. conditions, this translates into equilibration time scales on the order of min to tens of min, supporting the use of equil. partitioning in chem. transport models.
    40. 40
      Wei, J.; Fang, T.; Lakey, P. S. J.; Shiraiwa, M. Iron-Facilitated Organic Radical Formation from Secondary Organic Aerosols in Surrogate Lung Fluid. Environ. Sci. Technol. 2022, 56 (11), 7234– 7243,  DOI: 10.1021/acs.est.1c04334
      40
      Iron-Facilitated Organic Radical Formation from Secondary Organic Aerosols in Surrogate Lung Fluid
      Wei, Jinlai; Fang, Ting; Lakey, Pascale S. J.; Shiraiwa, Manabu
      Environmental Science & Technology (2022), 56 (11), 7234-7243CODEN: ESTHAG; ISSN:1520-5851. (American Chemical Society)
      Respiratory deposition of secondary org. aerosols (SOA) and iron may lead to the generation of reactive oxygen species and free radicals in lung fluid to cause oxidative stress, but their underlying mechanism and formation kinetics are not well understood. Here we demonstrate substantial formation of org. radicals in surrogate lung fluid (SLF) by mixts. of Fe2+ and SOA generated from photooxidn. of isoprene, α-terpineol, and toluene. The molar yields of org. radicals by SOA are measured to be 0.03-0.5% in SLF, which are 5-10 times higher than in water. We observe that Fe2+ enhances org. radical yields dramatically by a factor of 20-80, which can be attributed to Fe2+-facilitated decompn. of org. peroxides, in consistency with a pos. correlation between peroxide contents and org. radical yields. Ascorbate mediates redox cycling of iron ions to sustain org. peroxide decompn., as supported by kinetic modeling reproducing time- and concn.-dependence of org. radical formation as well as addnl. expts. observing the formation of Fe2+ and ascorbate radicals in mixts. of ascorbate and Fe3+. •OH and superoxide are found to be scavenged by antioxidants efficiently. These findings have implications on the role of org. radicals in oxidative damage and lipid peroxidn.
    41. 41
      Docherty, K. S.; Wu, W.; Lim, Y. B.; Ziemann, P. J. Contributions of Organic Peroxides to Secondary Aerosol Formed from Reactions of Monoterpenes with O3. Environ. Sci. Technol. 2005, 39 (11), 4049– 4059,  DOI: 10.1021/es050228s
      41
      Contributions of Organic Peroxides to Secondary Aerosol Formed from Reactions of Monoterpenes with O3
      Docherty, Kenneth S.; Wu, Wilbur; Lim, Yong Bin; Ziemann, Paul J.
      Environmental Science and Technology (2005), 39 (11), 4049-4059CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      The role of org. peroxides in secondary org. aerosol (SOA) formation from reactions of monoterpenes with O3 was investigated in a series of environmental chamber expts. Reactions were performed with endocyclic (α-pinene and Δ3-carene) and exocyclic (β-pinene and sabinene) alkenes in dry and humid air and in the presence of the OH radical scavengers: cyclohexane, 1-propanol, and formaldehyde. A thermal desorption particle beam mass spectrometer was used to probe the identity and volatility of SOA components, and an iodometric-spectrophotometric method was used to quantify org. peroxides. Thermal desorption profiles and mass spectra showed that the most volatile SOA components had vapor pressures similar to pinic acid and that much of the SOA consisted of less volatile species that were probably oligomeric compds. Peroxide analyses indicated that the SOA was predominantly org. peroxides, providing evidence that the oligomers were mostly peroxyhemiacetals formed by heterogeneous reactions of hydroperoxides and aldehydes. For example, it was estd. that org. peroxides contributed ∼47 and ∼85% of the SOA mass formed in the α- and β-pinene reactions, resp. Reactions performed with different OH radical scavengers indicated that most of the hydroperoxides were formed through the hydroperoxide channel rather than by reactions of stabilized Criegee intermediates. The effect of the OH radical scavenger on the SOA yield was also investigated, and the results were consistent with results of recent expts. and model simulations that support a mechanism based on changes in the [HO2]/[RO2] ratios. These are the first measurements of org. peroxides in monoterpene SOA, and the results have important implications for understanding the mechanisms of SOA formation and the potential effects of atm. aerosol particles on the environment and human health.
    42. 42
      Fang, T.; Verma, V.; Guo, H.; King, L. E.; Edgerton, E. S.; Weber, R. J. A Semi-Automated System for Quantifying the Oxidative Potential of Ambient Particles in Aqueous Extracts Using the Dithiothreitol (DTT) Assay: Results from the Southeastern Center for Air Pollution and Epidemiology (SCAPE). Atmospheric Meas. Technol. 2015, 8 (1), 471– 482,  DOI: 10.5194/amt-8-471-2015
      42
      A semi-automated system for quantifying the oxidative potential of ambient particles in aqueous extracts using the dithiothreitol (DTT) assay: results from the Southeastern Center for Air Pollution and Epidemiology (SCAPE)
      Fang, T.; Verma, V.; Guo, H.; King, L. E.; Edgerton, E. S.; Weber, R. J.
      Atmospheric Measurement Techniques (2015), 8 (1), 471-482CODEN: AMTTC2; ISSN:1867-8548. (Copernicus Publications)
      A variety of methods are used to measure the capability of particulate matter (PM) to catalytically generate reactive oxygen species (ROS) in vivo, also defined as the aerosol oxidative potential. A widely used measure of aerosol oxidative potential is the dithiothreitol (DTT) assay, which monitors the depletion of DTT (a surrogate for cellular antioxidants) as catalyzed by the redox-active species in PM. However, a major constraint in the routine use of the DTT assay for integrating it with large-scale health studies is its labor-intensive and time-consuming protocol. To specifically address this concern, we have developed a semi-automated system for quantifying the oxidative potential of aerosol liq. exts. using the DTT assay. The system, capable of unattended anal. at one sample per h, has a high anal. precision (coeff. of variation of 15% for pos. control, 4% for ambient samples) and reasonably low limit of detection (0.31 nmol min-1). Comparison of the automated approach with the manual method conducted on ambient samples yielded good agreement (slope = 1.08 ± 0.12, r2 = 0.92, N = 9). The system was utilized for the Southeastern Center for Air Pollution & Epidemiol. (SCAPE) to generate an extensive data set on DTT activity of ambient particles collected from contrasting environments (urban, roadside, and rural) in the southeastern US. We find that water-sol. PM2.5 DTT activity on a per-air-vol. basis was spatially uniform and often well correlated with PM2.5 mass (r = 0.49 to 0.88), suggesting regional sources contributing to the PM oxidative potential in the southeastern US. The correlation may also suggest a mechanistic explanation (oxidative stress) for obsd. PM2.5 mass-health assocns. The heterogeneity in the intrinsic DTT activity (per-PM-mass basis) across seasons indicates variability in the DTT activity assocd. with aerosols from sources that vary with season. Although developed for the DTT assay, the instrument can also be used to det. oxidative potential with other acellular assays.
    43. 43
      Chin, H.; Hopstock, K. S.; Fleming, L. T.; Nizkorodov, S. A.; Al-Abadleh, H. A. Effect of Aromatic Ring Substituents on the Ability of Catechol to Produce Brown Carbon in Iron(III)-Catalyzed Reactions. Environ. Sci. Atmospheres 2021, 1 (2), 64– 78,  DOI: 10.1039/D0EA00007H
      43
      Effect of aromatic ring substituents on the ability of catechol to produce brown carbon in iron(III)-catalyzed reactions
      Chin, Henry; Hopstock, Katherine S.; Fleming, Lauren T.; Nizkorodov, Sergey A.; Al-Abadleh, Hind A.
      Environmental Science: Atmospheres (2021), 1 (2), 64-78CODEN: ESANC9; ISSN:2634-3606. (Royal Society of Chemistry)
      Our previous work demonstrated formation of highly insol. and strongly light-absorbing org. particles in reactions between catechol or guaiacol with Fe(III) under pH = 3 conditions characteristic of aerosol liq. water. This work extends these measurements to reactions of Fe(III) with 2,4-dinitrophenol, 4-nitrocatechol, 4-methylcatechol, 1,2,4-benzenetriol, 1,2,3-benzenetriol (pyrogallol) and coniferaldehyde to better understand the mechanism of particle formation catalyzed by Fe(III). Particles were obsd. after 2 h of reactions of catechol (43 ± 1% mass yield), 1,2,4-benzenetriol (32 ± 3%), pyrogallol (27 ± 2%) and coniferaldehyde (35 ± 4%), while reactions of 2,4-dinitrophenol and 4-nitrocatechol did not produce any insol. products. No particles were obsd. in reaction of 4-methylcatechol after 2 h, however, insol. products appeared after a 24 h reaction time. Irradn. of a catechol + Fe(III) mixt. by 405 nm light was found to reduce (but not fully suppress) the particle yield due to a competition between photodegrdn. and Fe(III)-catalyzed oligomerization. Particles produced from precursors + Fe(III) solns. were dissolved in org. solvents and analyzed with ultra performance liq. chromatog. coupled to a photodiode array spectrophotometer and a high resoln. mass spectrometer. Major sepd. chromophores were identified as dimeric, trimeric, and tetrameric products of precursor mols. Purpurogallin was identified as a major reaction product of pyrogallol reaction with Fe(III). To test whether this chem. can occur in more realistic atm. aerosols, reactions of biomass burning org. aerosol (BBOA) exts. with Fe(III) were also examd. Two BBOA samples collected under flaming conditions produced no particles, whereas a BBOA sample produced under smoldering conditions resulted in particle formation under both dark and 405 nm irradn. conditions. The results suggest that Fe(III)-catalyzed chem. can take place in aging BBOA plumes resulting from smoldering fires and make aerosol particles more light-absorbing.
    44. 44
      Camredon, M.; Aumont, B.; Lee-Taylor, J.; Madronich, S. The SOA/VOC/NOx System: An Explicit Model of Secondary Organic Aerosol Formation. Atmospheric Chem. Phys. 2007, 7 (21), 5599– 5610,  DOI: 10.5194/acp-7-5599-2007
      44
      The SOA/VOC/NOx system: an explicit model of secondary organic aerosol formation
      Camredon, M.; Aumont, B.; Lee-Taylor, J.; Madronich, S.
      Atmospheric Chemistry and Physics (2007), 7 (21), 5599-5610CODEN: ACPTCE; ISSN:1680-7316. (Copernicus Publications)
      Our current understanding of secondary org. aerosol (SOA) formation is limited by our knowledge of gaseous secondary orgs. involved in gas/particle partitioning. The objective of this study is to explore (i) the potential for products of multiple oxidn. steps contributing to SOA, and (ii) the evolution of the SOA/VOC/NOx system. We developed an explicit model based on the coupling of detailed gas-phase oxidn. schemes with a thermodn. condensation module. Such a model allows prediction of SOA mass and speciation on the basis of first principles. The SOA/VOC/NOx system is studied for the oxidn. of 1-octene under atmospherically relevant concns. In this study, gaseous oxidn. of octene is simulated to lead to SOA formation. Contributors to SOA formation are shown to be formed via multiple oxidn. steps of the parent hydrocarbon. The behavior of the SOA/VOC/NOx system simulated using the explicit model agrees with general tendencies obsd. during lab. chamber expts. This explicit modeling of SOA formation appears as a useful exploratory tool to (i) support interpretations of SOA formation obsd. in lab. chamber expts., (ii) give some insights on SOA formation under atmospherically relevant conditions and (iii) investigate implications for the regional/global lifetimes of the SOA.
    45. 45
      Aumont, B.; Szopa, S.; Madronich, S. Modelling the Evolution of Organic Carbon during Its Gas-Phase Tropospheric Oxidation: Development of an Explicit Model Based on a Self Generating Approach. Atmospheric Chem. Phys. 2005, 5 (9), 2497– 2517,  DOI: 10.5194/acp-5-2497-2005
      45
      Modelling the evolution of organic carbon during its gas-phase tropospheric oxidation: Development of an explicit model based on a self generating approach
      Aumont, B.; Szopa, S.; Madronich, S.
      Atmospheric Chemistry and Physics (2005), 5 (9), 2497-2517CODEN: ACPTCE; ISSN:1680-7316. (European Geosciences Union)
      Org. compds. emitted in the atm. are oxidized in complex reaction sequences that produce a myriad of intermediates. Although the cumulative importance of these org. intermediates is widely acknowledged, there is still a crit. lack of information concerning the detailed compn. of the highly functionalized secondary orgs. in the gas and condensed phases. The evaluation of their impacts on pollution episodes, climate, and the tropospheric oxidizing capacity requires modeling tools that track the identity and reactivity of org. carbon in the various phases down to the ultimate oxidn. products, CO and CO2. However, a fully detailed representation of the atm. transformations of org. compds. involves a very large no. of intermediate species, far in excess of the no. that can be reasonably written manually. This paper describes (1) the development of a data processing tool to generate the explicit gas-phase oxidn. schemes of acyclic hydrocarbons and their oxidn. products under tropospheric conditions and (2) the protocol used to select the reaction products and the rate consts. Results are presented using the fully explicit oxidn. schemes generated for two test species: n-heptane and isoprene. Comparisons with well-established mechanisms were performed to evaluate these generated schemes. Some preliminary results describing the gradual change of org. carbon during the oxidn. of a given parent compd. are presented.
    46. 46
      Nannoolal, Y.; Rarey, J.; Ramjugernath, D. Estimation of Pure Component Properties. Fluid Phase Equilib. 2008, 269 (1-2), 117– 133,  DOI: 10.1016/j.fluid.2008.04.020
      46
      Estimation of pure component properties. Part 3. Estimation of the vapor pressure of non-electrolyte organic compounds via group contributions and group interaction
      Nannoolal, Yash; Rarey, Jurgen; Ramjugernath, Deresh
      Fluid Phase Equilibria (2008), 269 (1-2), 117-133CODEN: FPEQDT; ISSN:0378-3812. (Elsevier B.V.)
      A group contribution method for the estn. of the normal b.p. of nonelectrolyte org. compds., which was published earlier, has been the basis for development of subsequent phys. property methods. In this work, the model was extended to enable the prediction of vapor pressure data with special attention to the low-pressure region. The mol. structure of the compd. and a ref. point, usually the normal b.p., are the only required inputs and enables the estn. of vapor pressure at other temps. by group contribution. The structural group definitions are similar to those proposed earlier for the normal b.p., with minor modifications having been made to improve the predictions. Structural groups were defined in a standardized form and fragmentation of the mol. structures was performed by an automatic procedure to eliminate any arbitrary assumptions. The new method is based on vapor pressure data for more than 1600 components. The results of the new method are compared to the Antoine correlative equation using parameters stored in the Dortmund Data Bank, as well as, the DIPPR vapor pressure correlations. The group contribution method has proven to be a good predictor, with accuracies comparable to the correlations. Moreover, because the regression of group contributions was performed for a large no. of compds., the results can in several cases be considered more reliable than those of the correlative models that were regressed to individual components only. The range of the method is usually from about the triple or m.p. to a reduced temp. of 0.75-0.8.
    47. 47
      Vereecken, L.; Peeters, J. Decomposition of Substituted Alkoxy Radicals─Part I: A Generalized Structure–Activity Relationship for Reaction Barrier Heights. Phys. Chem. Chem. Phys. 2009, 11 (40), 9062– 9074,  DOI: 10.1039/b909712k
      47
      Decomposition of substituted alkoxy radicals-part I: a generalized structure-activity relationship for reaction barrier heights
      Vereecken, L.; Peeters, J.
      Physical Chemistry Chemical Physics (2009), 11 (40), 9062-9074CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      An update and expansion of our readily applicable structure-activity relationship (SAR) for predicting the barrier height Eb to decompn. by β C-C scission of (substituted) alkoxy radicals is presented. Such alkoxy radicals are key intermediates in the atm. oxidn. of volatile org. compds., and a correct description of their chem. is vital to the understanding of atm. chem.; nevertheless, exptl. data on these reactions remain scarce. The SAR is based on quantum chem. characterizations of a large set of alkoxy radicals, and accommodates alkoxy radicals with alkyl- (-R), oxo- (=O), hydroxy- (-OH), hydroperoxy (-OOH), alkoxy (-OR), alkylperoxy- (-OOR), nitroso- (-NO), nitro- (-NO2), nitrosooxy- (-ONO), and nitroxy- (-ONO2) functionalities, as well as 3- to 6-membered rings and some unsatd. side chains. The SAR expresses the barrier height to decompn., Eb = 17.9 kcal mol-1 + ΣNs×Fs, as a linear function of the no. Ns of these substituents on the relevant carbons, and the substituent-specific activities Fs derived from the quantum chem. calcns., allowing facile predictions based solely on the mol. structure. For low barriers, ≤7 kcal mol-1, a simple curvature correction is required. The SAR-predicted barrier height Eb can be used to predict the high-pressure rate coeff. for alkoxy decompn. kdiss at or around 298 K.
    48. 48
      Jenkin, M. E.; Valorso, R.; Aumont, B.; Rickard, A. R. Estimation of Rate Coefficients and Branching Ratios for Reactions of Organic Peroxy Radicals for Use in Automated Mechanism Construction. Atmospheric Chem. Phys. 2019, 19 (11), 7691– 7717,  DOI: 10.5194/acp-19-7691-2019
      48
      Estimation of rate coefficients and branching ratios for reactions of organic peroxy radicals for use in automated mechanism construction
      Jenkin, Michael E.; Valorso, Richard; Aumont, Bernard; Rickard, Andrew R.
      Atmospheric Chemistry and Physics (2019), 19 (11), 7691-7717CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      Org. peroxy radicals (RO2), formed from the degrdn. of hydrocarbons and other volatile org. compds. (VOCs), play a key role in tropospheric oxidn. mechanisms. Several competing reactions may be available for a given RO2 radical, the relative rates of which depend on both the structure of RO2 and the ambient conditions. Published kinetics and branching ratio data are reviewed for the bimol. reactions of RO2 with NO, NO2, NO3, OH and HO2; and for their self-reactions and cross-reactions with other RO2 radicals. This information is used to define generic rate coeffs. and structure-activity relationship (SAR) methods that can be applied to the bimol. reactions of a series of important classes of hydrocarbon and oxygenated RO2 radicals. Information for selected unimol. isomerization reactions (i.e. H-atom shift and ring-closure reactions) is also summarized and discussed. The methods presented here are intended to guide the representation of RO2 radical chem. in the next generation of explicit detailed chem. mechanisms.
    49. 49
      McVay, R. C.; Zhang, X.; Aumont, B.; Valorso, R.; Camredon, M.; La, Y. S.; Wennberg, P. O.; Seinfeld, J. H. SOA Formation from the Photooxidation of α-Pinene: Systematic Exploration of the Simulation of Chamber Data. Atmospheric Chem. Phys. 2016, 16 (5), 2785– 2802,  DOI: 10.5194/acp-16-2785-2016
      49
      SOA formation from the photooxidation of α-pinene: systematic exploration of the simulation of chamber data
      McVay, Renee C.; Zhang, Xuan; Aumont, Bernard; Valorso, Richard; Camredon, Marie; La, Yuyi S.; Wennberg, Paul O.; Seinfeld, John H.
      Atmospheric Chemistry and Physics (2016), 16 (5), 2785-2802CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      Chem. mechanisms play an important role in simulating the atm. chem. of volatile org. compd. oxidn. Comparison of mechanism simulations with lab. chamber data tests our level of understanding of the prevailing chem. as well as the dynamic processes occurring in the chamber itself. α-Pinene photooxidn. is a well-studied system exptl., for which detailed chem. mechanisms have been formulated. Here, we present the results of simulating low-NO α-pinene photooxidn. expts. conducted in the Caltech chamber with the Generator for Explicit Chem. and Kinetics of Orgs. in the Atm. (GECKO-A) under varying concns. of seed particles and OH levels. Unexpectedly, expts. conducted at low and high OH levels yield the same secondary org. aerosol (SOA) growth, whereas GECKO-A predicts greater SOA growth under high OH levels. SOA formation in the chamber is a result of a competition among the rates of gas-phase oxidn. to low-volatility products, wall deposition of these products, and condensation into the aerosol phase. Various processes - such as photolysis of condensed-phase products, particle-phase dimerization, and peroxy radical autoxidn. - are explored to rationalize the observations. In order to explain the obsd. similar SOA growth at different OH levels, we conclude that vapor wall loss in the Caltech chamber is likely of order 10-5 s-1, consistent with previous exptl. measurements in that chamber.We find that GECKO-A tends to overpredict the contribution to SOA of later-generation oxidn. products under high-OH conditions. Moreover, we propose that autoxidn. may alternatively resolve some or all of the measurement-model discrepancy, but this hypothesis cannot be confirmed until more explicit mechanisms are established for α-pinene autoxidn. The key role of the interplay among oxidn. rate, product volatility, and vapor-wall deposition in chamber expts. is illustrated.
    50. 50
      Galeazzo, T.; Valorso, R.; Li, Y.; Camredon, M.; Aumont, B.; Shiraiwa, M. Estimation of Secondary Organic Aerosol Viscosity from Explicit Modeling of Gas-Phase Oxidation of Isoprene and α-Pinene. Atmospheric Chem. Phys. 2021, 21 (13), 10199– 10213,  DOI: 10.5194/acp-21-10199-2021
      50
      Estimation of secondary organic aerosol viscosity from explicit modeling of gas-phase oxidation of isoprene and α-pinene
      Galeazzo, Tommaso; Valorso, Richard; Li, Ying; Camredon, Marie; Aumont, Bernard; Shiraiwa, Manabu
      Atmospheric Chemistry and Physics (2021), 21 (13), 10199-10213CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      Secondary org. aerosols (SOA) are major components of atm. fine particulate matter, affecting climate and air quality. Mounting evidence exists that SOA can adopt glassy and viscous semisolid states, impacting formation and partitioning of SOA. In this study, we apply the GECKO-A (Generator of Explicit Chem. and Kinetics of Orgs. in the Atm.) model to conduct explicit chem. modeling of isoprene photooxidn. and α-pinene ozonolysis and their subsequent SOA formation. The detailed gas-phase chem. schemes from GECKO-A are implemented into a box model and coupled to our recently developed glass transition temp. parameterizations, allowing us to predict SOA viscosity. The effects of chem. compn., relative humidity, mass loadings and mass accommodation on particle viscosity are investigated in comparison with measurements of SOA viscosity. The simulated viscosity of isoprene SOA agrees well with viscosity measurements as a function of relative humidity, while the model underestimates viscosity of α-pinene SOA by a few orders of magnitude. This difference may be due to missing processes in the model, including autoxidn. and particle-phase reactions, leading to the formation of high-molar-mass compds. that would increase particle viscosity. Addnl. simulations imply that kinetic limitations of bulk diffusion and redn. in mass accommodation coeff. may play a role in enhancing particle viscosity by suppressing condensation of semi-volatile compds. The developed model is a useful tool for anal. and investigation of the interplay among gas-phase reactions, particle chem. compn. and SOA phase state.
    51. 51
      Smith, N. R.; Crescenzo, G. V.; Huang, Y.; Hettiyadura, A. P. S.; Siemens, K.; Li, Y.; Faiola, C. L.; Laskin, A.; Shiraiwa, M.; Bertram, A. K.; Nizkorodov, S. A. Viscosity and Liquid–Liquid Phase Separation in Healthy and Stressed Plant SOA. Environ. Sci. Atmospheres 2021, 1 (3), 140– 153,  DOI: 10.1039/D0EA00020E
      51
      Viscosity and liquid-liquid phase separation in healthy and stressed plant SOA
      Smith, Natalie R.; Crescenzo, Giuseppe V.; Huang, Yuanzhou; Hettiyadura, Anusha P. S.; Siemens, Kyla; Li, Ying; Faiola, Celia L.; Laskin, Alexander; Shiraiwa, Manabu; Bertram, Allan K.; Nizkorodov, Sergey A.
      Environmental Science: Atmospheres (2021), 1 (3), 140-153CODEN: ESANC9; ISSN:2634-3606. (Royal Society of Chemistry)
      Mol. compn., viscosity, and liq.-liq. phase sepn. (LLPS) were investigated for secondary org. aerosol (SOA) derived from synthetic mixts. of volatile org. compds. (VOCs) representing emission profiles for Scots pine trees under healthy and aphid-herbivory stress conditions. Model "healthy plant SOA"and "stressed plant SOA" were generated in a 5 m3 environmental smog chamber by photooxidn. of the mixts. at 50% relative humidity (RH). SOA from photooxidn. of α-pinene was also prepd. for comparison. Mol. compn. was detd. with high resoln. mass spectrometry, viscosity was detd. with the poke-flow technique, and liq.-liq. phase sepn. was investigated with optical microscopy. The stressed plant SOA had increased abundance of higher mol. wt. species, reflecting a greater fraction of sesquiterpenes in the stressed VOC mixt. compared to the healthy plant VOC mixt. LLPS occurred in both the healthy and stressed plant SOA; however, stressed plant SOA exhibited phase sepn. over a broader humidity range than healthy plant SOA, with LLPS persisting down to 23 ± 11% RH. At RH ≤25%, both stressed and healthy plant SOA viscosity exceeded 108 Pa s, a value similar to that of tar pitch. At 40% and 50% RH, stressed plant SOA had the highest viscosity, followed by healthy plant SOA and then α-pinene SOA in descending order. The obsd. peak abundances in the mass spectra were also used to est. the SOA viscosity as a function of RH and volatility. The predicted viscosity of the healthy plant SOA was lower than that of the stressed plant SOA driven by both the higher glass transition temps. and lower hygroscopicity of the org. mols. making up stressed plant SOA. These findings suggest that plant stress influences the physicochem. properties of biogenic SOA. Furthermore, a complex mixt. of VOCs resulted in a higher SOA viscosity compared to SOA generated from α-pinene alone at ≥25% RH, highlighting the importance of studying properties of SOA generated from more realistic multi-component VOC mixts.
    52. 52
      Trump, E. R.; Epstein, S. A.; Riipinen, I.; Donahue, N. M. Wall Effects in Smog Chamber Experiments: A Model Study. Aerosol Sci. Technol. 2016, 50 (11), 1180– 1200,  DOI: 10.1080/02786826.2016.1232858
      52
      Wall effects in smog chamber experiments: A model study
      Trump, Erica R.; Epstein, Scott A.; Riipinen, Ilona; Donahue, Neil M.
      Aerosol Science and Technology (2016), 50 (11), 1180-1200CODEN: ASTYDQ; ISSN:0278-6826. (Taylor & Francis, Inc.)
      Wall losses of condensable org. vapors are a significant complication for smog-chamber expts. designed to constrain prodn. of Secondary Org. Aerosols (SOA). Here we develop a dynamical mass-balance model based on the Volatility Basis Set (VBS) to explore various pathways for mass transfer between the bulk of a smog-chamber vol. (the vapors and suspended particles) and reservoirs near the chamber walls (deposited and/or nucleated particles on the walls, adsorption to the walls, and sorption into Teflon walls). We consider various limiting cases and explore the sensitivity of inferred SOA yields to assumptions about the actual parameters in a given SOA expt. We also present data suggesting that adsorptive uptake to Teflon for typical SOA is modest. Broadly, we find that walls become a sink for condensable vapors when those vapors interact with either deposited particles of the Teflon walls, with qual. similar effects on the suspended particles. Finally, we show that having a relatively high seed condensation sink is vital to reliable chamber mass balances. Copyright 2016 American Assocn. for Aerosol Research.
    53. 53
      Ye, P.; Ding, X.; Hakala, J.; Hofbauer, V.; Robinson, E. S.; Donahue, N. M. Vapor Wall Loss of Semi-Volatile Organic Compounds in a Teflon Chamber. Aerosol Sci. Technol. 2016, 50 (8), 822– 834,  DOI: 10.1080/02786826.2016.1195905
      53
      Vapor wall loss of semi-volatile organic compounds in a Teflon chamber
      Ye, Penglin; Ding, Xiang; Hakala, Jani; Hofbauer, Victoria; Robinson, Ellis S.; Donahue, Neil M.
      Aerosol Science and Technology (2016), 50 (8), 822-834CODEN: ASTYDQ; ISSN:0278-6826. (Taylor & Francis, Inc.)
      We have investigated the vapor wall loss of semi-volatile org. compds. (SVOCs) in a Teflon smog chamber. We studied the vapor wall loss of seven SVOCs with known satn. concns., including alkanes (hexacosane, pentacosane, docosane, eicosane, and d62-squalane), an org. acid (oleic acid), and a polyol (levoglucosan) in single-component and binary-component (org.) systems, using ammonium sulfate (AS) seeds to constrain the particle wall loss. We coated inorg. particles with SVOCs and measured the loss of orgs. from those particles to constrain the wall losses, observing loss rates proportional to the satn. concns. of the SVOCs. The loss rate of oleic acid mixed with d62-squalane was proportional to its mole fraction in the mixt. Our results show that the vapor wall-loss rates of SVOCs are significant, quasi-irreversible, and proportional to the SVOC vapor concns. The vapor wall-loss rate const. of the SVOCs that we studied in the CMU chamber is 3.8 ± 0.3 h-1; this is comparable to values in other chambers with similar surface area to vol. ratios. Our results are also consistent with a relatively high mass accommodation coeff. for SVOCs, αorg > 0.1. Copyright 2016 American Assocn. for Aerosol Research.
    54. 54
      Ditto, J. C.; Joo, T.; Khare, P.; Sheu, R.; Takeuchi, M.; Chen, Y.; Xu, W.; Bui, A. A. T.; Sun, Y.; Ng, N. L.; Gentner, D. R. Effects of Molecular-Level Compositional Variability in Organic Aerosol on Phase State and Thermodynamic Mixing Behavior. Environ. Sci. Technol. 2019, 53 (22), 13009– 13018,  DOI: 10.1021/acs.est.9b02664
      54
      Effects of Molecular-Level Compositional Variability in Organic Aerosol on Phase State and Thermodynamic Mixing Behavior
      Ditto, Jenna C.; Joo, Taekyu; Khare, Peeyush; Sheu, Roger; Takeuchi, Masayuki; Chen, Yunle; Xu, Weiqi; Bui, Alexander A. T.; Sun, Yele; Ng, Nga L.; Gentner, Drew R.
      Environmental Science & Technology (2019), 53 (22), 13009-13018CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      The mol.-level compn. and structure of org. aerosol (OA) affect its physicochem. properties, transformations, and impacts. This work used the mol.-level chem. compn. of functionalized OA from three diverse field sites to evaluate the effect of mol.-level compositional variability on OA phase state and thermodn. mixing favorability. For these ambient sites, modeled aerosol phase state ranged from liq. to semi-solid. OA compn. obsd. variability had some effect on the resulting phase state, but other factors (e.g., the presence of inorg. ions, aerosol liq. water, internal vs. external mixing with water) were detg. factors in whether these particles exist as liqs., semi-solids, or solids. Org. mol. compn. played a more important role in detg. phase state for phase-sepd. (vs. well-mixed) systems. Despite obsd. OA compositional differences, the thermodn. mixing favorability for OA samples with aerosol liq. water, isoprene oxidn. products, or monoterpene oxidn. products remained fairly consistent within each campaign. Mixing of filter-sampled OA and isoprene or monoterpene oxidn. products is often favorable in both seasons, while mixing with water is generally unfavorable.
    55. 55
      Schervish, M.; Donahue, N. M. Peroxy Radical Chemistry and the Volatility Basis Set. Atmospheric Chem. Phys. 2020, 20 (2), 1183– 1199,  DOI: 10.5194/acp-20-1183-2020
      55
      Peroxy radical chemistry and the volatility basis set
      Schervish, Meredith; Donahue, Neil M.
      Atmospheric Chemistry and Physics (2020), 20 (2), 1183-1199CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      Gas-phase autoxidn. of orgs. can generate highly oxygenated org. mols. (HOMs) and thus increase secondary org. aerosol prodn. and enable newparticle formation. Here we present a new implementation of the volatility basis set (VBS) that explicitly resolves peroxy radical (RO2) products formed via autoxidn. The model includes a strong temp. dependence for autoxidn. as well as explicit termination of RO2, including reactions with NO, HO2, and other RO2. The RO2 cross-reactions can produce dimers (ROOR). We explore the temp. and NOx dependence of this chem., showing that temp. strongly influences the intrinsic volatility distribution and that NO can suppress autoxidn. under conditions typically found in the atm.
    56. 56
      Schervish, M.; Donahue, N. M. Peroxy Radical Kinetics and New Particle Formation. Environ. Sci. Atmospheres 2021, 1 (2), 79– 92,  DOI: 10.1039/D0EA00017E
      56
      Peroxy radical kinetics and new particle formation
      Schervish, Meredith; Donahue, Neil M.
      Environmental Science: Atmospheres (2021), 1 (2), 79-92CODEN: ESANC9; ISSN:2634-3606. (Royal Society of Chemistry)
      Chamber expts. showing "pure biogenic nucleation" have shown an important role for covalently bound org. assocn. products ("dimers"). These form from peroxy-radical (RO2) cross reactions. Chamber expts. at low-NOx conditions often have quite high hydrocarbon reactant concns. and relatively low concns. of oxygenated volatile org. compds. (OVOCs). This can skew the radical chem. in chambers relative to the real atm., favoring RO2 and disfavoring HO2 radicals. RO2 cross reaction kinetics are in turn highly uncertain. Here we explore the implications of the RO2 to HO2 ratio in chamber expts. as well as the implications of uncertain RO2 cross reaction kinetics and the potential for added CO to mimic more atm. radical conditions. We treat a plausible range of RO2 rate coeffs. under both typical chamber conditions and atm. conditions to see how dimerization is affected by high concns. of OVOCs, and thus lower RO2 : HO2 relative to smog chamber expts. We find that if RO2 reactions are fast, relatively high yields of low volatility dimers can participate in new particle formation. The results are highly sensitive to both the (uncertain) RO2 kinetics as well as RO2 : HO2, suggesting both that low-NOx chamber results should be extrapolated to the atm. with caution but also that the atm. itself may be highly sensitive to the specific (and rich) mixt. of org. compds. and thus peroxy radicals.
    57. 57
      Abdel-Shafy, H. I.; Mansour, M. S. M. A Review on Polycyclic Aromatic Hydrocarbons: Source, Environmental Impact, Effect on Human Health and Remediation. Egypt. J. Pet. 2016, 25 (1), 107– 123,  DOI: 10.1016/j.ejpe.2015.03.011
      There is no corresponding record for this reference.
    58. 58
      Kautzman, K. E.; Surratt, J. D.; Chan, M. N.; Chan, A. W. H.; Hersey, S. P.; Chhabra, P. S.; Dalleska, N. F.; Wennberg, P. O.; Flagan, R. C.; Seinfeld, J. H. Chemical Composition of Gas- and Aerosol-Phase Products from the Photooxidation of Naphthalene. J. Phys. Chem. A 2010, 114 (2), 913– 934,  DOI: 10.1021/jp908530s
      58
      Chemical Composition of Gas- and Aerosol-Phase Products from the Photooxidation of Naphthalene
      Kautzman, K. E.; Surratt, J. D.; Chan, M. N.; Chan, A. W. H.; Hersey, S. P.; Chhabra, P. S.; Dalleska, N. F.; Wennberg, P. O.; Flagan, R. C.; Seinfeld, J. H.
      Journal of Physical Chemistry A (2010), 114 (2), 913-934CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      A detailed evolution of the chem. compn. of the gas- and aerosol-phase constituents produced from OH--initiated photooxidn. of naphthalene under low- and high-NOx conditions is reported. Under high-NOx conditions, ring-opening products are the primary gas-phase products, suggesting the mechanism involves dissocn. of alkoxy radicals (RO) formed via an RO2 + NO pathway, or a bicyclic peroxy mechanism. In contrast to high-NOx chem., ring-retaining compds. appeared to dominate the low-NOx gas-phase products due to the RO2 + HO2 pathway. The authors chem. characterized 53-68% of the secondary org. aerosol (SOA) mass. At. O:C (O:C), H:C, and N:C ratios measured in bulk samples by high-resoln. electro-spray ionization time-of-flight mass spectrometry (HR-ESI-TOFMS) are the same as ratios obsd. with online high-resoln. time-of-flight aerosol mass spectrometry (HR-ToF-AMS), suggesting the chem. compns. and oxidn. levels obsd. in the chem.-characterized fraction of the particle phase are representative of the bulk aerosol. Oligomers, organosulfates (R-OSO3), and other high mol. wt. products were not obsd. in either low- or high-NOx SOA; however, in the presence of a neutral (NH4)2SO4 seed aerosol, an org. sulfonic acid (R-SO3), characterized as hydroxybenzene sulfonic acid, was obsd. in naphthalene SOA produced under high- and low-NOx conditions. Acid compds. and org. peroxides accounted for a large fraction of chem. characterized high- and low-NOx SOA. The authors propose the major gas- and aerosol-phase products obsd. were generated via formation and further reaction of 2-formylcinnamaldehyde or a bicyclic peroxy intermediate. The chem. similarity between lab. SOA and ambient aerosol collected at Birmingham, Alabama, and Pasadena, California, confirmed the importance of polycyclic arom. hydrocarbon oxidn. for aerosol formation in the urban atm.
    59. 59
      Odinga, E. S.; Waigi, M. G.; Gudda, F. O.; Wang, J.; Yang, B.; Hu, X.; Li, S.; Gao, Y. Occurrence, Formation, Environmental Fate and Risks of Environmentally Persistent Free Radicals in Biochars. Environ. Int. 2020, 134, 105172,  DOI: 10.1016/j.envint.2019.105172
      59
      Occurrence, formation, environmental fate and risks of environmentally persistent free radicals in biochars
      Odinga, Emmanuel Stephen; Waigi, Michael Gatheru; Gudda, Fredrick Owino; Wang, Jian; Yang, Bing; Hu, Xiaojie; Li, Shunyao; Gao, Yanzheng
      Environment International (2020), 134 (), 105172CODEN: ENVIDV; ISSN:0160-4120. (Elsevier Ltd.)
      Biochars are used globally in agricultural crop prodn. and environmental remediation. However, environmentally persistent free radicals (EPFRs), which are stable emerging pollutants, are generated as a characteristic feature during biomass pyrolysis. EPFRs can induce the formation of reactive oxygen species, which poses huge agro-environmental and human health risks. Their half-lives and persistence in both biochar residues and in the atm. may lead to potentially adverse risks in the environment. This review highlights the comprehensive research into these bioreactive radicals, as well as the bottlenecks of biochar prodn. leading up to the formation and persistence of EPFRs. Addnl., a way forward has been proposed, based on two main recommendations. A global joint initiative to create an all-encompassing regulations policy document that will improve both the technol. and the quality control aspects of biochars to reduce EPFR generation at the prodn. level. Furthermore, environmental impact and risk assessment studies should be conducted in the extensive applications of biochars in order to protect the environmental and human health. The highlighted key research directions proposed herein will shape the prodn., research, and adoption aspects of biochars, which will mitigate the considerable concerns raised on EPFRs.
    60. 60
      Wei, J.; Fang, T.; Shiraiwa, M. Effects of Acidity on Reactive Oxygen Species Formation from Secondary Organic Aerosols. ACS Environ. Au 2022, 2 (4), 336– 345,  DOI: 10.1021/acsenvironau.2c00018
      60
      Effects of Acidity on Reactive Oxygen Species Formation from Secondary Organic Aerosols
      Wei, Jinlai; Fang, Ting; Shiraiwa, Manabu
      ACS Environmental Au (2022), 2 (4), 336-345CODEN: AEACC4; ISSN:2694-2518. (American Chemical Society)
      Reactive oxygen species (ROS) play a crit. role in the chem. transformation of atm. secondary org. aerosols (SOA) and aerosol health effects by causing oxidative stress in vivo. Acidity is an important physicochem. property of atm. aerosols, but its effects on the ROS formation from SOA have been poorly characterized. By applying the ESR spin-trapping technique and the Diogenes chemiluminescence assay, we find highly distinct radical yields and compn. at different pH values in the range of 1-7.4 from SOA generated by oxidn. of isoprene, α-terpineol, α-pinene, β-pinene, toluene, and naphthalene. We observe that isoprene SOA has substantial hydroxyl radical (•OH) and org. radical yields at neutral pH, which are 1.5-2 times higher compared to acidic conditions in total radical yields. Superoxide (O2•-) is found to be the dominant species generated by all types of SOAs at lower pH. At neutral pH, α-terpineol SOA exhibits a substantial yield of carbon-centered org. radicals, while no radical formation is obsd. by arom. SOA. Further expts. with model compds. show that the decompn. of org. peroxide leading to radical formation may be suppressed at lower pH due to acid-catalyzed rearrangement of peroxides. We also observe 1.5-3 times higher molar yields of hydrogen peroxide (H2O2) in acidic conditions compared to neutral pH by biogenic and arom. SOA, likely due to enhanced decompn. of α-hydroxyhydroperoxides and quinone redox cycling, resp. These findings are crit. to bridge the gap in understanding ROS formation mechanisms and kinetics in atm. and physiol. environments.
    61. 61
      Kramer, A. J.; Rattanavaraha, W.; Zhang, Z.; Gold, A.; Surratt, J. D.; Lin, Y.-H. Assessing the Oxidative Potential of Isoprene-Derived Epoxides and Secondary Organic Aerosol. Atmos. Environ. 2016, 130, 211– 218,  DOI: 10.1016/j.atmosenv.2015.10.018
      61
      Assessing the oxidative potential of isoprene-derived epoxides and secondary organic aerosol
      Kramer, Amanda J.; Rattanavaraha, Weruka; Zhang, Zhenfa; Gold, Avram; Surratt, Jason D.; Lin, Ying-Hsuan
      Atmospheric Environment (2016), 130 (), 211-218CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
      Fine particulate matter (PM2.5) is known to contribute to adverse health effects, such as asthma, cardiopulmonary disease, and lung cancer. Secondary org. aerosol (SOA) is a major component of PM2.5 and can be enhanced by atm. oxidn. of biogenic volatile org. compds. in the presence of anthropogenic pollutants, such as nitrogen oxides (NOx) and sulfur dioxide. However, whether biogenic SOA contributes to adverse health effects remains unclear. The objective of this study was to assess the potential of isoprene-derived epoxides and SOA for generating reactive oxygen species (ROS) in light of the recent recognition that atm. oxidn. of isoprene in the presence of acidic sulfate aerosol is a major contributor to the global SOA burden. The dithiothreitol (DTT) assay was used to characterize the ROS generation by the isoprene-derived epoxides, trans-β-isoprene epoxydiol (trans-β-IEPOX) and methacrylic acid epoxide (MAE), and their hydrolysis products, the 2-methyltetrol diastereomers (2-MT), 2-methylglyceric acid (2-MG), their organosulfate derivs., as well as an isoprene-derived hydroxyhydroperoxide (ISOPOOH). In addn., ROS generation potential was evaluated for total SOA produced from photooxidn. of isoprene and methacrolein (MACR) as well as from the reactive uptake of trans-β-IEPOX and MAE onto acidified sulfate aerosol. The high-NOx regime, which yields 2-MG-, MAE- and MACR-derived SOA has a higher ROS generation potential than the low-NOx regime, which yields 2-MT, IEPOX- and isoprene-derived SOA. ISOPOOH has an ROS generation potential similar to 1,4-naphthoquinone (1,4-NQ), suggesting a significant contribution of aerosol-phase org. peroxides to PM oxidative potential. MAE- and MACR-derived SOA show equal or greater ROS generation potential than reported in studies on diesel exhaust PM, highlighting the importance of a comprehensive investigation of the toxicity of isoprene-derived SOA.
    62. 62
      McWhinney, R. D.; Zhou, S.; Abbatt, J. P. D. Naphthalene SOA: Redox Activity and Naphthoquinone Gas–Particle Partitioning. Atmospheric Chem. Phys. 2013, 13 (19), 9731– 9744,  DOI: 10.5194/acp-13-9731-2013
      62
      Naphthalene SOA: redox activity and naphthoquinone gas-particle partitioning
      McWhinney, R. D.; Zhou, S.; Abbatt, J. P. D.
      Atmospheric Chemistry and Physics (2013), 13 (19), 9731-9744, 14 pp.CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      Chamber secondary org. aerosol (SOA) from low-NOx photooxidn. of naphthalene by hydroxyl radical was examd. with respect to its redox cycling behavior using the dithiothreitol (DTT) assay. Naphthalene SOA was highly redox-active, consuming DTT at an av. rate of 118 ± 14 pmol per min per μg of SOA material. Measured particle-phase masses of the major previously identified redox active products, 1,2- and 1,4-naphthoquinone, accounted for only 21 ± 3% of the obsd. redox cycling activity. The redox-active 5-hydroxy-1,4-naphthoquinone was identified as a new minor product of naphthalene oxidn., and including this species in redox activity predictions increased the predicted DTT reactivity to 30 ± 5 % of observations. These results suggest that there are substantial unidentified redox-active SOA constituents beyond the small quinones that may be important toxic components of these particles. A gas-to-SOA particle partitioning coeff. was calcd. to be (7.0 ± 2.5) × 10-4 m3 μg-1 for 1,4-naphthoquinone at 25 °C. This value suggests that under typical warm conditions, 1,4-naphthoquinone is unlikely to contribute strongly to redox behavior of ambient particles, although further work is needed to det. the potential impact under conditions such as low temps. where partitioning to the particle is more favorable. Also, higher order oxidn. products that likely account for a substantial fraction of the redox cycling capability of the naphthalene SOA are likely to partition much more strongly to the particle phase.
    63. 63
      Tuet, W. Y.; Chen, Y.; Xu, L.; Fok, S.; Gao, D.; Weber, R. J.; Ng, N. L. Chemical Oxidative Potential of Secondary Organic Aerosol (SOA) Generated from the Photooxidation of Biogenic and Anthropogenic Volatile Organic Compounds. Atmospheric Chem. Phys. 2017, 17 (2), 839– 853,  DOI: 10.5194/acp-17-839-2017
      63
      Chemical oxidative potential of secondary organic aerosol (SOA) generated from the photooxidation of biogenic and anthropogenic volatile organic compounds
      Tuet, Wing Y.; Chen, Yunle; Xu, Lu; Fok, Shierly; Gao, Dong; Weber, Rodney J.; Ng, Nga L.
      Atmospheric Chemistry and Physics (2017), 17 (2), 839-853CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      Particulate matter (PM), of which a significant fraction is comprised of secondary org. aerosols (SOA), has received considerable attention due to its health implications. In this study, the water-sol. oxidative potential (OPWS) of SOA generated from the photooxidn. of biogenic and anthropogenic hydrocarbon precursors (isoprene, α-pinene, β-caryophyllene, pentadecane, m-xylene, and naphthalene) under different reaction conditions ("RO2+HO2" vs. "RO2+NO" dominant, dry vs. humid) was characterized using dithiothreitol (DTT) consumption. The measured intrinsic OPWS-DTT values ranged from 9 to 205 pmol min-1 μg-1 and were highly dependent on the specific hydrocarbon precursor, with naphthalene and isoprene SOA generating the highest and lowest OPWS-DTT values, resp. Humidity and RO2 fate affected OPWS-DTT in a hydrocarbon-specific manner, with naphthalene SOA exhibiting the most pronounced effects, likely due to the formation of nitroaroms. Together, these results suggest that precursor identity may be more influential than reaction condition in detg. SOA oxidative potential, demonstrating the importance of sources, such as incomplete combustion, to aerosol toxicity. In the context of other PM sources, all SOA systems, with the exception of naphthalene SOA, were less DTT active than ambient sources related to incomplete combustion, including diesel and gasoline combustion as well as biomass burning. Finally, naphthalene SOA was as DTT active as biomass burning aerosol, which was found to be the most DTT-active OA source in a previous ambient study. These results highlight a need to consider SOA contributions (particularly from anthropogenic hydrocarbons) to health effects in the context of hydrocarbon emissions, SOA yields, and other PM sources.
    64. 64
      Tong, H.; Zhang, Y.; Filippi, A.; Wang, T.; Li, C.; Liu, F.; Leppla, D.; Kourtchev, I.; Wang, K.; Keskinen, H.-M. Radical Formation by Fine Particulate Matter Associated with Highly Oxygenated Molecules. Environ. Sci. Technol. 2019, 53 (21), 12506– 12518,  DOI: 10.1021/acs.est.9b05149
      64
      Radical Formation by Fine Particulate Matter Associated with Highly Oxygenated Molecules
      Tong, Haijie; Zhang, Yun; Filippi, Alexander; Wang, Ting; Li, Chenpei; Liu, Fobang; Leppla, Denis; Kourtchev, Ivan; Wang, Kai; Keskinen, Helmi-Marja; Levula, Janne T.; Arangio, Andrea M.; Shen, Fangxia; Ditas, Florian; Martin, Scot T.; Artaxo, Paulo; Godoi, Ricardo H. M.; Yamamoto, Carlos I.; de Souza, Rodrigo A. F.; Huang, Ru-Jin; Berkemeier, Thomas; Wang, Yueshe; Su, Hang; Cheng, Yafang; Pope, Francis D.; Fu, Pingqing; Yao, Maosheng; Poehlker, Christopher; Petaejae, Tuukka; Kulmala, Markku; Andreae, Meinrat O.; Shiraiwa, Manabu; Poeschl, Ulrich; Hoffmann, Thorsten; Kalberer, Markus
      Environmental Science & Technology (2019), 53 (21), 12506-12518CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Highly oxygenated mols. (HOMs) play an important role in the formation and evolution of secondary org. aerosols (SOA). However, the abundance of HOMs in different environments and their relation to the oxidative potential of fine particulate matter (PM) are largely unknown. Here, we investigated the relative HOM abundance and radical yield of lab.-generated SOA and fine PM in ambient air ranging from remote forest areas to highly polluted megacities. By ESR and mass spectrometric investigations, we found that the relative abundance of HOMs, esp. the dimeric and low-volatility types, in ambient fine PM was pos. correlated with the formation of radicals in aq. PM exts. SOA from photooxidn. of isoprene, ozonolysis of α- and β-pinene, and fine PM from tropical (central Amazon) and boreal (Hyyti.ovrddot.al.ovrddot.a, Finland) forests exhibited a higher HOM abundance and radical yield than SOA from photooxidn. of naphthalene and fine PM from urban sites (Beijing, Guangzhou, Mainz, Shanghai, and Xi'an), confirming that HOMs are important constituents of biogenic SOA to generate radicals. Our study provides new insights into the chem. relationship of HOM abundance, compn., and sources with the yield of radicals by lab. and ambient aerosols, enabling better quantification of the component-specific contribution of source- or site-specific fine PM to its climate and health effects.
    65. 65
      Grosjean, D.; Grosjean, E.; Williams, E. L. Thermal Decomposition of PAN, PPN and Vinyl-PAN. Air Waste 1994, 44 (4), 391– 396,  DOI: 10.1080/1073161X.1994.10467260
      65
      Thermal decomposition of PAN, PPN and vinyl-PAN
      Grosjean, Daniel; Grosjean, Eric; Williams, Edwin L.
      Air & Waste (1994), 44 (4), 391-6CODEN: AIWAE2; ISSN:1073-161X.
      The gas phase thermal decompn. rates of the C1 and C2-substituted peroxyacyl nitrates (RC(O)OONO2), PAN (R=CH3), PPN (R=C2H5) and vinyl-PAN (R= CH2=CH-) were measured at 288-299 K and 1 atm. of air. The results for PAN are consistent with literature data. Thermal decompn. rates for PPN and vinyl-PAN are similar to that for PAN, with k298 = 3.0 × 10-4/s for PAN, 3.4 × 10-4/s for PPN, and 3.0 × 10-4/s for vinyl-PAN. Implications for the atm. persistence of PPN and vinyl-PAN as compared to that of PAN are discussed.
    66. 66
      von Ahsen, S.; Willner, H.; Francisco, J. S. Thermal Decomposition of Peroxy Acetyl Nitrate CH3C(O)OONO2. J. Chem. Phys. 2004, 121 (5), 2048– 2057,  DOI: 10.1063/1.1767813
      66
      Thermal decomposition of peroxy acetyl nitrate CH3C(O)OONO2
      von Ahsen, Stefan; Willner, Helge; Francisco, Joseph S.
      Journal of Chemical Physics (2004), 121 (5), 2048-2057CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      The thermal decompn. of peroxy acetyl nitrate (PAN) is investigated by low pressure flash thermolysis of PAN highly dild. in noble gases and subsequent isolation of the products in noble gas matrixes at low temps. and by d. functional computations. The IR spectroscopically obsd. formation of CH3C(O)OO and H2CCO (ketene) besides NO2, CO2, and HOO implies a unimol. decay pathway for the thermal decompn. of PAN. The major decompn. reaction of PAN is bond fission of the O-N single bond yielding the peroxy radical. The O-O bond fission pathway is a minor route. In the latter case the primary reaction products undergo secondary reactions whose products are spectroscopically identified. No evidence for rearrangement processes as the formation of Me nitrate is obsd. A detailed mapping of the reaction pathways for primary and secondary reactions using quantum chem. calcns. is in good agreement with the expt. and predicts homolytic O-N and O-O bond fissions within the PAN mol. as the lowest energetic primary processes. In addn., the first IR spectroscopic characterization of two rotameric forms for the radical CH3C(O)OO is given.
    67. 67
      Bunce, N. J.; Liu, L.; Zhu, J.; Lane, D. A. Reaction of Naphthalene and Its Derivatives with Hydroxyl Radicals in the Gas Phase. Environ. Sci. Technol. 1997, 31 (8), 2252– 2259,  DOI: 10.1021/es960813g
      67
      Reaction of Naphthalene and Its Derivatives with Hydroxyl Radicals in the Gas Phase
      Bunce, Nigel J.; Liu, Lina; Zhu, Jiang; Lane, Douglas A.
      Environmental Science and Technology (1997), 31 (8), 2252-2259CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Naphthalene is the most abundant polycyclic arom. hydrocarbon (PAH) found in urban air. It is reactive in the atm. under ambient conditions, its chief reaction partner being the hydroxyl radical, OH•. In this work, the reactions of OH• with naphthalene, 1- and 2-naphthol, and 1- and 2-nitronaphthalene were studied in a 9.4 m3 smog chamber. Relative rates of reaction accorded well with previous studies and allowed ests. to be made of the atm. lifetimes of these compds. Numerous oxidn. products were identified, and mechanisms proposed for their formation were based on the further transformation of benzocyclohexadienyl radicals formed by addn. of OH• to naphthalene. The naphthols and nitronaphthalenes were deduced not to be on the major reaction pathway to the more oxidized products. Because of the high reactivity of PAH in air, we suggest that priority be given to identifying and quantitating their reaction products, some of which may be relatively persistent air toxics.
    68. 68
      Nozière, B.; Barnes, I.; Becker, K.-H. Product Study and Mechanisms of the Reactions of α-Pinene and of Pinonaldehyde with OH Radicals. J. Geophys. Res. Atmospheres 1999, 104 (D19), 23645– 23656,  DOI: 10.1029/1999JD900778
      68
      Product study and mechanisms of the reactions of α-pinene and of pinonaldehyde with OH radicals
      Noziere, Barbara; Barnes, Ian; Becker, Karl-Heinz
      Journal of Geophysical Research, [Atmospheres] (1999), 104 (D19), 23645-23656CODEN: JGRDE3 ISSN:. (American Geophysical Union)
      The reactions of α-pinene and of its main oxidn. product, pinonaldehyde (3-acetyl-2,2-dimethyl-cyclobutyl-ethanal), with OH radicals have been studied in the lab. using Fourier transform IR spectroscopy for real-time monitoring of the gas-phase chem. species and a Scanning Mobility Particle Sizer system (3071 A, TSI) for the study of the secondary aerosol formation. All gas-phase molar yields were quantified using calibrated ref. of the pure compd., except for the nitrates products. The results were: for the α-pinene expts. in the presence of NOx, pinonaldehyde, (87 ± 20)%; total nitrates (18 ± 9)%; formaldehyde, (23 ± 9)%; acetone (9 ± 6)%; for the α-pinene expts. in the absence of NOx: pinonaldehyde, (37 ± 7)%; formaldehyde, (8 ± 1)%; acetone, (7 ± 2)%; for the pinonaldehyde expts. in the presence of nitric oxide, formaldehyde (152 ± 56)% and acetone (15 ± 7)%. The aerosol measurements showed that the condensed products accounted for the missing carbon in the gas-phase balance. The partitioning of the products into the condensed phase was found to be potentially significant under exptl. conditions but less than 10% for initial α-pinene concns. lower than 1013 mol. cm-3 and hence negligible under atm. conditions in the absence of aerosol seeds. On the basis of these results a comprehensive mechanism for the gas-phase reaction of α-pinene with OH in the presence of NOx has been proposed, including quant. values for all the involved branching ratios.
    69. 69
      Romonosky, D. E.; Laskin, A.; Laskin, J.; Nizkorodov, S. A. High-Resolution Mass Spectrometry and Molecular Characterization of Aqueous Photochemistry Products of Common Types of Secondary Organic Aerosols. J. Phys. Chem. A 2015, 119 (11), 2594– 2606,  DOI: 10.1021/jp509476r
      69
      High-Resolution Mass Spectrometry and Molecular Characterization of Aqueous Photochemistry Products of Common Types of Secondary Organic Aerosols
      Romonosky, Dian E.; Laskin, Alexander; Laskin, Julia; Nizkorodov, Sergey A.
      Journal of Physical Chemistry A (2015), 119 (11), 2594-2606CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      This work presents a systematic assessment of the mol. level compn. and extent of aq. photochem. processing in different types of secondary org. aerosols (SOA) from biogenic and anthropogenic precursors, including α-pinene, β-pinene, β-myrcene, D-limonene, α-humulene, 1,3,5-trimethylbenzene, and guaiacol, oxidized by O3 (simulating a remote atm.) or by OH- in the presence of NOx (simulating an urban atm.). Chamber- and flow-tube-generated SOA samples were collected, extd. in a methanol/water soln., and photolyzed for 1 h under identical irradn. conditions. In these expts., irradn. was equiv. to ∼3-8 h exposure to the sun at its zenith. The mol. level compn. of dissolved SOA was probed before and after photolysis with direct-infusion electro-spray ionization high-resoln. mass spectrometry. Mass spectra of un-photolyzed SOA generated by O3 oxidn. of monoterpenes showed qual. similar features and contained largely overlapping subsets of identified compds. Mass spectra of OH-/NOx-generated SOA had a more unique visual appearance and indicated a lower extent of product overlap. The fraction of N-contg. species (organonitrates, nitroaroms.) was highly sensitive to the SOA precursor. These observations suggested that attributing high-resoln. mass spectra in field SOA samples to specific SOA precursors should be more straight-forward under OH-/NOx oxidn. conditions vs. O3-driven oxidn. Comparing SOA constituents before and after photolysis showed a tendency to reduce the av. no. of atoms in the SOA compds. without a significant effect on overall O:C and H:C ratios. SOA prepd. by OH-/NOx photooxidn. of 1,3,5-trimethylbenzene and guaiacol were more resilient to photolysis despite being the most light-absorbing. The compn. of SOA prepd. by ozonolysis of monoterpenes changed more significantly as a result of photolysis. Results indicated aq. photolysis of dissolved SOA compds. in cloud/fog water can occur in various types of SOA and on atmospherically relevant time scales. However, the extent of the photolysis-driven changes in mol. compn. depended on the specific type of SOA.
    70. 70
      Romonosky, D. E.; Li, Y.; Shiraiwa, M.; Laskin, A.; Laskin, J.; Nizkorodov, S. A. Aqueous Photochemistry of Secondary Organic Aerosol of α-Pinene and α-Humulene Oxidized with Ozone, Hydroxyl Radical, and Nitrate Radical. J. Phys. Chem. A 2017, 121 (6), 1298– 1309,  DOI: 10.1021/acs.jpca.6b10900
      70
      Aqueous Photochemistry of Secondary Organic Aerosol of α-Pinene and α-Humulene Oxidized with Ozone, Hydroxyl Radical, and Nitrate Radical
      Romonosky, Dian E.; Li, Ying; Shiraiwa, Manabu; Laskin, Alexander; Laskin, Julia; Nizkorodov, Sergey A.
      Journal of Physical Chemistry A (2017), 121 (6), 1298-1309CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      Formation of secondary org. aerosols (SOA) from biogenic volatile org. compds. (BVOC) occurs via O3- and OH-initiated reactions during the day and reactions with NO3 during the night. We explored the effect of these three oxidn. conditions on the mol. compn. and aq. photochem. of model SOA prepd. from two common BVOC. A common monoterpene, α-pinene, and sesquiterpene, α-humulene, were used to form SOA in a smog chamber via BVOC + O3, BVOC + NO3, and BVOC + OH + NOx oxidn. Samples of SOA were collected on filters, water-sol. compds. from SOA were extd. in water, and the resulting aq. solns. were photolyzed to simulate the photochem. aq. processing of SOA. The extent of change in the mol. level compn. of SOA over 4 h of photolysis (approx. equiv. to 64 h of photolysis under ambient conditions) was assessed with high-resoln. electrospray ionization mass spectrometry. The anal. revealed significant differences in the mol. compn. between SOA formed by the different oxidn. pathways. The compn. further evolved during photolysis with the most notable change corresponding to the nearly complete removal of nitrogen-contg. org. compds. Hydrolysis of SOA compds. also occurred in parallel with photolysis. The preferential loss of larger SOA compds. during photolysis and hydrolysis made the SOA compds. more volatile on av. This study suggests that aq. processes may under certain conditions lead to a redn. in the SOA loading as opposed to an increase in SOA loading commonly assumed in the literature.
    71. 71
      Siemens, K.; Morales, A.; He, Q.; Li, C.; Hettiyadura, A. P. S.; Rudich, Y.; Laskin, A. Molecular Analysis of Secondary Brown Carbon Produced from the Photooxidation of Naphthalene. Environ. Sci. Technol. 2022, 56 (6), 3340– 3353,  DOI: 10.1021/acs.est.1c03135
      71
      Molecular Analysis of Secondary Brown Carbon Produced from the Photooxidation of Naphthalene
      Siemens, Kyla; Morales, Ana; He, Quanfu; Li, Chunlin; Hettiyadura, Anusha P. S.; Rudich, Yinon; Laskin, Alexander
      Environmental Science & Technology (2022), 56 (6), 3340-3353CODEN: ESTHAG; ISSN:1520-5851. (American Chemical Society)
      We investigate the chem. compn. of org. light-absorbing components, also known as brown carbon (BrC) chromophores, formed in a proxy of anthropogenic secondary org. aerosol generated from the photooxidn. of naphthalene (naph-SOA) in the absence and presence of NOx. High-performance liq. chromatog. equipped with a photodiode array detector and electrospray ionization high-resoln. mass spectrometer is employed to characterize naph-SOA and its BrC components. We provide mol.-level insights into the chem. compn. and optical properties of individual naph-SOA components and investigate their BrC relevance. This work reveals the formation of strongly absorbing nitro-arom. chromophores under high-NOx conditions and describes their degrdn. during atm. aging. NOx addn. enhanced the light absorption of naph-SOA while reducing wavelength-dependence, as seen by the mass absorption coeff. (MAC) and absorption Ångstr.ovrddot.om exponent (AAE). Optical parameters of naph-SOA generated under low- and high-NOx conditions showed a range of values from MACOM 405nm ~ 0.12 m2 g-1 and AAE300-450nm ~ 8.87 (low-NOx) to MACOM 405nm ~ 0.19 m2 g-1 and AAE300-450nm ~ 7.59 (high-NOx), consistent with "very weak" and "weak" BrC optical classes, resp. The weak-BrC class is commonly attributed to biomass smoldering emissions, which appear to have optical properties comparable with the naph-SOA. Mol. chromophores contributing to naphthalene BrC absorption were identified with substantial nitro-aroms., indicating that these species may be used as source-specific markers of BrC related to the anthropogenic emissions.
    72. 72
      Lee, H. J.; Aiona, P. K.; Laskin, A.; Laskin, J.; Nizkorodov, S. A. Effect of Solar Radiation on the Optical Properties and Molecular Composition of Laboratory Proxies of Atmospheric Brown Carbon. Environ. Sci. Technol. 2014, 48 (17), 10217– 10226,  DOI: 10.1021/es502515r
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      Effect of solar radiation on the optical properties and molecular composition of laboratory proxies of atmospheric brown carbon
      Lee, Hyun Ji; Aiona, Paige Kuuipo; Laskin, Alexander; Laskin, Julia; Nizkorodov, Sergey A.
      Environmental Science & Technology (2014), 48 (17), 10217-10226CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Sources, optical properties, and chem. compn. of atm. brown carbon (BrC) aerosol are uncertain, making it challenging to est. its contribution to radiative forcing. Furthermore, optical properties of BrC may change significantly during its atm. aging. We examd. the effect of photolysis on the mol. compn., mass absorption coeff., and fluorescence of secondary org. aerosol (SOA) prepd. by high-NOx photooxidn. of naphthalene (NAP SOA). Our expts. were designed to model photolysis processes of NAP SOA compds. dissolved in cloud or fog droplets. Aq. solns. of NAP SOA were obsd. to photobleach (i.e., lose their ability to absorb visible radiation) with an effective half-life of ∼15 h (with sun in its zenith) for the loss of near-UV (300-400 nm) absorbance. The mol. compn. of NAP SOA was significantly modified by photolysis, with the av. SOA formula changing from C14.1H14.5O5.1N0.085 to C11.8H14.9O4.5N0.023 after 4 h of irradn. However, the av. O/C ratio did not change significantly, suggesting that it is not a good metric for assessing the extent of photolysis-driven aging in NAP SOA (and in BrC in general). In contrast to NAP SOA, the photobleaching of BrC material produced by the reaction of limonene + ozone SOA with ammonia vapor (aged LIM/O3 SOA) was much faster, but it did not result in a significant change in av. mol. compn. The characteristic absorbance of the aged LIM/O3 SOA in the 450-600 nm range decayed with an effective half-life of <0.5 h. These results emphasize the highly variable and dynamic nature of different types of atm. BrC.
    73. 73
      Vasquez, K. T.; Crounse, J. D.; Schulze, B. C.; Bates, K. H.; Teng, A. P.; Xu, L.; Allen, H. M.; Wennberg, P. O. Rapid Hydrolysis of Tertiary Isoprene Nitrate Efficiently Removes NOx from the Atmosphere. Proc. Natl. Acad. Sci. U. S. A. 2020, 117 (52), 33011– 33016,  DOI: 10.1073/pnas.2017442117
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      Rapid hydrolysis of tertiary isoprene nitrate efficiently removes NOx from the atmosphere
      Vasquez, Krystal T.; Crounse, John D.; Schulze, Benjamin C.; Bates, Kelvin H.; Teng, Alexander P.; Xu, Lu; Allen, Hannah M.; Wennberg, Paul O.
      Proceedings of the National Academy of Sciences of the United States of America (2020), 117 (52), 33011-33016CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      The formation of a suite of isoprene-derived hydroxy nitrate (IHN) isomers during the OH-initiated oxidn. of isoprene affects both the concn. and distribution of nitrogen oxide free radicals (NOx). Expts. performed in an atm. simulation chamber suggest that the lifetime of the most abundant isomer, 1,2-IHN, is shortened significantly by a water-mediated process (leading to nitric acid formation), while the lifetime of a similar isomer, 4,3-IHN, is not. Consistent with these chamber studies, NMR kinetic expts. constrain the 1,2-IHN hydrolysis lifetime to \<10 s in deuterium oxide (D2O) at 298 K, whereas the 4,3-IHN isomer was obsd. to hydrolyze much less efficiently. These lab. findings are used to interpret observations of the IHN isomer distribution in ambient air. The IHN isomer ratio (1,2-IHN to 4,3-IHN) in a high NOx environment decreases rapidly in the afternoon, which is not explained using known gas-phase chem. When simulated with an observationally constrained model, we find that an addnl. loss process for the 1,2-IHN isomer with a time const. of ∼6 h best explains our atm. measurements. Using ests. for 1,2-IHN Henry's law const. and atm. liq. water vol., we show that condensed-phase hydrolysis of 1,2-IHN can account for this loss process. Simulations from a global chem. transport model show that the hydrolysis of 1,2-IHN accounts for a substantial fraction of NOx lost (and HNO3 produced), resulting in large impacts on oxidant formation, esp. over forested regions.
    74. 74
      Kurtén, T.; Rissanen, M. P.; Mackeprang, K.; Thornton, J. A.; Hyttinen, N.; Jørgensen, S.; Ehn, M.; Kjaergaard, H. G. Computational Study of Hydrogen Shifts and Ring-Opening Mechanisms in α-Pinene Ozonolysis Products. J. Phys. Chem. A 2015, 119 (46), 11366– 11375,  DOI: 10.1021/acs.jpca.5b08948
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      Computational Study of Hydrogen Shifts and Ring-Opening Mechanisms in α-Pinene Ozonolysis Products
      Kurten, Theo; Rissanen, Matti P.; Mackeprang, Kasper; Thornton, Joel A.; Hyttinen, Noora; Joergensen, Solvejg; Ehn, Mikael; Kjaergaard, Henrik G.
      Journal of Physical Chemistry A (2015), 119 (46), 11366-11375CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      Autoxidn. by sequential peroxy radical hydrogen shifts (H-shifts) and O2 addns. has recently emerged as a promising mechanism for the rapid formation of highly oxidized, low-volatility org. compds. in the atm. A key prerequisite for autoxidn. is that the H-shifts of the initial peroxy radicals formed by, e.g., OH or O3 oxidn. are fast enough to compete with bimol. sink reactions. In most atm. conditions, these restrict the lifetime of peroxy radicals to be on the order of seconds. We have systematically investigated all potentially important (nonmethyl, sterically unhindered) H-shifts of all four peroxy radicals formed in the ozonolysis of α-pinene using d. functional (ωB97XD) and coupled cluster [CCSD(T)-F12] theory. In contrast to the related but chem. simpler cyclohexene ozonolysis system, none of the calcd. H-shifts have rate consts. above 1 s-1 at 298 K, and most are below 0.01 s-1. The low rate consts. are connected to the presence of the strained cyclobutyl ring in the α-pinene-derived peroxy radicals, which hinders H-shifts both from and across the ring. For autoxidn. to yield the exptl. obsd. highly oxidized products in the α-pinene ozonolysis system, addnl. ring-opening reaction mechanisms breaking the cyclobutyl ring are therefore needed. We further investigate possible uni- and bimol. pathways for opening the cyclobutyl ring in the α-pinene ozonolysis system.
    75. 75
      Li, Y.; Shiraiwa, M. Timescales of Secondary Organic Aerosols to Reach Equilibrium at Various Temperatures and Relative Humidities. Atmospheric Chem. Phys. 2019, 19 (9), 5959– 5971,  DOI: 10.5194/acp-19-5959-2019
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      Timescales of secondary organic aerosols to reach equilibrium at various temperatures and relative humiditie
      Li, Ying; Shiraiwa, Manabu
      Atmospheric Chemistry and Physics (2019), 19 (9), 5959-5971CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      Secondary org. aerosols (SOA) account for a substantial fraction of air particulate matter, and SOA formation is often modeled assuming rapid establishment of gas-particle equil. Here, we est. the characteristic timescale for SOA to achieve gas-particle equil. under a wide range of temps. and relative humidities using a state-of-the-art kinetic flux model. Equilibration timescales were calcd. by varying particle phase state, size, mass loadings, and volatility of org. compds. in open and closed systems. Model simulations suggest that the equilibration timescale for semi-volatile compds. is on the order of seconds or minutes for most conditions in the planetary boundary layer, but it can be longer than 1 h if particles adopt glassy or amorphous solid states with high glass transition temps. at low relative humidity. The timescale of partitioning of low-volatile compds. into highly viscous particles is shorter compared to semi-volatile compds. in the closed system, as it is largely detd. by condensation sink due to very slow re-evapn. with relatively quick establishment of local equil. between the gas phase and the near-surface bulk. The dependence of equilibration timescales on both volatility and bulk diffusivity provides crit. insights into thermodn. or kinetic treatments of SOA partitioning for accurate predictions of gas- and particle-phase concns. of semi-volatile compds. in regional and global chem. transport models.
    76. 76
      Shiraiwa, M.; Pöschl, U. Mass Accommodation and Gas–Particle Partitioning in Secondary Organic Aerosols: Dependence on Diffusivity, Volatility, Particle-Phase Reactions, and Penetration Depth. Atmospheric Chem. Phys. 2021, 21 (3), 1565– 1580,  DOI: 10.5194/acp-21-1565-2021
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      Mass accommodation and gas-particle partitioning in secondary organic aerosols: dependence on diffusivity, volatility, particle-phase reactions, and penetration depth
      Shiraiwa, Manabu; Poeschl, Ulrich
      Atmospheric Chemistry and Physics (2021), 21 (3), 1565-1580CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      Mass accommodation is an essential process for gas-particle partitioning of org. compds. in secondary org. aerosols (SOA). The mass accommodation coeff. is commonly described as the probability of a gas mol. colliding with the surface to enter the particle phase. It is often applied, however, without specifying if and how deep a mol. has to penetrate beneath the surface to be regarded as being incorporated into the condensed phase (adsorption vs. absorption). While this aspect is usually not crit. for liq. particles with rapid surface-bulk exchange, it can be important for viscous semi-solid or glassy solid particles to distinguish and resolve the kinetics of accommodation at the surface, transfer across the gas-particle interface, and further transport into the particle bulk. For this purpose, we introduce a novel parameter: an effective mass accommodation coeff. aeff that depends on penetration depth and is a function of surface accommodation coeff., volatility, bulk diffusivity, and particlephase reaction rate coeff. Application of aeff in the traditional Fuchs-Sutugin approxn. of mass-transport kinetics at the gas-particle interface yields SOA partitioning results that are consistent with a detailed kinetic multilayer model (kinetic multilayer model of gas-particle interactions in aerosols and clouds, KM-GAP; Shiraiwa et al., 2012) and two-film model solns. (Model for Simulating Aerosol Interactions and Chem., MOSAIC; Zaveri et al., 2014) but deviate substantially from earlier modeling approaches not considering the influence of penetration depth and related parameters. For highly viscous or semi-solid particles, we show that the effective mass accommodation coeff. remains similar to the surface accommodation coeff. in the case of low-volatility compds., whereas it can decrease by several orders of magnitude in the case of semi-volatile compds. Such effects can explain apparent inconsistencies between earlier studies deriving mass accommodation coeffs. from exptl. data or from mol. dynamics simulations. Our findings challenge the approach of traditional SOA models using the Fuchs-Sutugin approxn. of mass transfer kinetics with a fixed mass accommodation coeff., regardless of particle phase state and penetration depth. The effective mass accommodation coeff. introduced in this study provides an efficient new way of accounting for the influence of volatility, diffusivity, and particle-phase reactions on SOA partitioning in process models as well as in regional and global air quality models. While kinetic limitations may not be crit. for partitioning into liq. SOA particles in the planetary boundary layer (PBL), the effects are likely important for amorphous semi-solid or glassy SOA in the free and upper troposphere (FT-UT) as well as in the PBL at low relative humidity and low temp.
    77. 77
      Zhang, Y.; Chen, Y.; Lambe, A. T.; Olson, N. E.; Lei, Z.; Craig, R. L.; Zhang, Z.; Gold, A.; Onasch, T. B.; Jayne, J. T. Effect of the Aerosol-Phase State on Secondary Organic Aerosol Formation from the Reactive Uptake of Isoprene-Derived Epoxydiols (IEPOX). Environ. Sci. Technol. Lett. 2018, 5 (3), 167– 174,  DOI: 10.1021/acs.estlett.8b00044
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      Effect of the Aerosol-Phase State on Secondary Organic Aerosol Formation from the Reactive Uptake of Isoprene-Derived Epoxydiols (IEPOX)
      Zhang, Yue; Chen, Yuzhi; Lambe, Andrew T.; Olson, Nicole E.; Lei, Ziying; Craig, Rebecca L.; Zhang, Zhenfa; Gold, Avram; Onasch, Timothy B.; Jayne, John T.; Worsnop, Douglas R.; Gaston, Cassandra J.; Thornton, Joel A.; Vizuete, William; Ault, Andrew P.; Surratt, Jason D.
      Environmental Science & Technology Letters (2018), 5 (3), 167-174CODEN: ESTLCU; ISSN:2328-8930. (American Chemical Society)
      Acid-catalyzed reactions between gas- and particle-phase constituents are crit. to atm. secondary org. aerosol (SOA) formation. The aerosol-phase state is thought to influence the reactive uptake of gas-phase precursors to aerosol particles by altering diffusion rates within particles. However, few exptl. studies have explored the precise role of the aerosol-phase state on reactive uptake processes. This lab. study systematically examines the reactive uptake coeff. (γ) of trans-β-isoprene epoxydiol (trans-β-IEPOX), the predominant IEPOX isomer, on acidic sulfate particles coated with SOA derived from α-pinene ozonolysis. γIEPOX is obtained for core-shell particles, the morphol. of which was confirmed by microscopy, as a function of SOA coating thickness and relative humidity. γIEPOX is reduced, in some cases by half of the original value, when SOA coatings are present prior to uptake, esp. when coating thicknesses are >15 nm. The diurnal trend of IEPOX lost to acid-catalyzed reactive uptake yielding SOA compared with other known atm. sinks (gas-phase oxidn. or deposition) is derived by modeling the exptl. coating effect with field data from the southeastern United States. IEPOX-derived SOA is estd. to be reduced by 16-27% due to preexisting org. coatings during the afternoon (12:00 to 7:00 p.m., local time), corresponding to the period with the highest level of prodn.
    78. 78
      Huang, Y.; Mahrt, F.; Xu, S.; Shiraiwa, M.; Zuend, A.; Bertram, A. K. Coexistence of Three Liquid Phases in Individual Atmospheric Aerosol Particles. Proc. Natl. Acad. Sci. U. S. A. 2021, 118 (16), e2102512118,  DOI: 10.1073/pnas.2102512118
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      Coexistence of three liquid phases in individual atmospheric aerosol particles
      Huang, Yuanzhou; Mahrt, Fabian; Xu, Shaun; Shiraiwa, Manabu; Zuend, Andreas; Bertram, Allan K.
      Proceedings of the National Academy of Sciences of the United States of America (2021), 118 (16), e2102512118CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      Individual atm. particles can contain mixts. of primary org. aerosol (POA), secondary org. aerosol (SOA), and secondary inorg. aerosol (SIA). To predict the role of such complex multicomponent particles in air quality and climate, information on the no. and types of phases present in the particles is needed. However, the phase behavior of such particles has not been studied in the lab., and as a result, remains poorly constrained. Here, we show that POA+SOA+SIA particles can contain three distinct liq. phases: a low-polarity org.-rich phase, a higher-polarity org.-rich phase, and an aq. inorg.-rich phase. Based on our results, when the elemental oxygen-to-carbon (O:C) ratio of the SOA is \<0.8, three liq. phases can coexist within the same particle over a wide relative humidity range. In contrast, when the O:C ratio of the SOA is greater than 0.8, three phases will not form. We also demonstrate, using thermodn. and kinetic modeling, that the presence of three liq. phases in such particles impacts their equilibration timescale with the surrounding gas phase. Three phases will likely also impact their ability to act as nuclei for liq. cloud droplets, the reactivity of these particles, and the mechanism of SOA formation and growth in the atm. These observations provide fundamental information necessary for improved predictions of air quality and aerosol indirect effects on climate.