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Comparing i-Tree Eco Estimates of Particulate Matter Deposition with Leaf and Canopy Measurements in an Urban Mediterranean Holm Oak Forest

  • Rocco Pace
    Rocco Pace
    Institute of Research on Terrestrial Ecosystems (IRET), National Research Council (CNR), Porano (TR), 05010, Italy
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    Orcidhttp://orcid.org/0000-0002-3126-635X
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  • Gabriele Guidolotti*
    Gabriele Guidolotti
    Institute of Research on Terrestrial Ecosystems (IRET), National Research Council (CNR), Porano (TR), 05010, Italy
    *Email: [email protected]
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    Orcidhttp://orcid.org/0000-0002-2052-6523
  • , 
  • Chiara Baldacchini
    Chiara Baldacchini
    Institute of Research on Terrestrial Ecosystems (IRET), National Research Council (CNR), Porano (TR), 05010, Italy
    Biophysics and Nanoscience Centre, Department of Ecological and Biological Sciences (DEB), University of Tuscia, Viterbo, 01100, Italy
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    Orcidhttp://orcid.org/0000-0002-5268-6572
  • , 
  • Emanuele Pallozzi
    Emanuele Pallozzi
    Institute of Research on Terrestrial Ecosystems (IRET), National Research Council (CNR), Monterotondo Scalo (RM), 00015, Italy
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  • , 
  • Rüdiger Grote
    Rüdiger Grote
    Institute of Meteorology and Climate Research, Atmospheric Environmental Research (IMK-IFU), Karlsruhe Institute of Technology (KIT), Garmisch-Partenkirchen, 82467, Germany
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  • David J. Nowak
    David J. Nowak
    USDA Forest Service, Northern Research Station, Syracuse, New York 13210, United States
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  • Carlo Calfapietra
    Carlo Calfapietra
    Institute of Research on Terrestrial Ecosystems (IRET), National Research Council (CNR), Porano (TR), 05010, Italy
    More by Carlo Calfapietra
    Orcidhttp://orcid.org/0000-0001-5040-4343
Cite this: Environ. Sci. Technol. 2021, 55, 10, 6613–6622
Publication Date (Web):April 28, 2021
https://doi.org/10.1021/acs.est.0c07679

Copyright © 2022 The Authors. Published by American Chemical Society. This publication is licensed under

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Abstract

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Trees and urban forests remove particulate matter (PM) from the air through the deposition of particles on the leaf surface, thus helping to improve air quality and reduce respiratory problems in urban areas. Leaf deposited PM, in turn, is either resuspended back into the atmosphere, washed off during rain events or transported to the ground with litterfall. The net amount of PM removed depends on crown and leaf characteristics, air pollution concentration, and weather conditions, such as wind speed and precipitation. Many existing deposition models, such as i-Tree Eco, calculate PM2.5 removal using a uniform deposition velocity function and resuspension rate for all tree species, which vary based on leaf area and wind speed. However, model results are seldom validated with experimental data. In this study, we compared i-Tree Eco calculations of PM2.5 deposition with fluxes determined by eddy covariance assessments (canopy scale) and particulate matter accumulated on leaves derived from measurements of vacuum/filtration technique as well as scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (leaf scale). These investigations were carried out at the Capodimonte Royal Forest in Naples. Modeled and measured fluxes showed good overall agreement, demonstrating that net deposition mostly happened in the first part of the day when atmospheric PM concentration is higher, followed by high resuspension rates in the second part of the day, corresponding with increased wind speeds. The sensitivity analysis of the model parameters showed that a better representation of PM deposition fluxes could be achieved with adjusted deposition velocities. It is also likely that the standard assumption of a complete removal of particulate matter, after precipitation events that exceed the water storage capacity of the canopy (Ps), should be reconsidered to better account for specific leaf traits. These results represent the first validation of i-Tree Eco PM removal with experimental data and are a starting point for improving the model parametrization and the estimate of particulate matter removed by urban trees.

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Synopsis

Cross evaluation of modeled airborne PM2.5 deposition with experimental measurements to properly estimate the contribution of urban green spaces to air quality improvement.

Introduction

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Improving air quality is a priority in many urban areas because pollution concentration often exceeds thresholds established by national or international legislation. (1) One of the most dangerous pollutants is fine particulate matter (PM2.5) because tiny particles can be inhaled and affect the respiratory system. (2) The concentration of these particles is affected by the balance between the pollutant emission, formation, and atmospheric conditions, and pollutant removal by wet and dry deposition to various surfaces. The main sources of airborne particulate matter are not only human activities (industries, households, and vehicles) but also natural ones such as wind-blown desert dust particles or sea spray aerosols. (3)
For dry deposition, vegetation represents one of the most effective sinks. (4) To decrease the concentration of airborne particles, nature-based solutions, including an increased abundance of trees, due to their high leaf exposure surface (LAI), has been suggested as a sustainable approach for air pollution mitigation. (5,6) However, vegetation properties as well as climatic conditions affect the efficiency of particle removal because PM is not only deposited on the vegetation surfaces but is also washed off during rain events (or transported to the ground with litterfall) and resuspended into the atmosphere. (7) The net amount of PM removed thus depends on crown and leaf characteristics, air pollution concentration, and weather conditions, such as wind speed and precipitation. (8−10)
Consequently, relatively complex models are needed to evaluate the overall removal, which can help decision makers to optimize vegetation management and planting programs. The i-Tree model (7) together with Computational Fluid Dynamics (CFD) simulations (11,12) are the most common models to estimate PM removal from urban vegetation. These models are based on relatively coarse assumptions with only little consideration of leaf traits. For example, the i-Tree Eco model, which is the most commonly used urban forest model to evaluate a number of ecosystem services of urban trees, (13) uses common deposition velocity procedures and resuspension rates for all tree species based on total leaf area and wind speed. (7)
However, the ability of tree species to capture and retain PM on leaf surfaces varies according to foliar traits (14) such as epicuticular waxes, (15) trichome density, (16) and surface roughness. (17) In addition, conifers are generally more efficient at capturing PM2.5 than broadleaved species (18) due to their needle-like leaves which are smaller and more effectively arranged, resulting in a larger leaf area exposure (LAD). (19,20) Due to these uncertainty factors, (13) a first sensitivity study on the i-Tree Eco assumptions was recently carried out, suggesting the distinguishing of deposition velocities for conifers and broadleaves. (21)
Evaluation of model estimates with PM deposition data at canopy or leaf level is relatively seldom described in the literature. A good correlation was found between simulated PM10 deposition on tree crowns, using a CFD pollutant dispersion model (ENVI-met), and PM quantified on leaves, with Saturation Isothermal Remanent Magnetization (SIRM). (22) Eddy covariance (EC) measurements have also been used to evaluate PM deposition models. (23,24)
In general, various approaches exist to assess different properties of leaf deposited PM, many of them based on detailed leaf assessment such as vacuum/filtration (VF) technique, (25−28) atomic absorption spectroscopy (AAS), (29,30) inductively coupled plasma atomic emission spectroscopy (ICP-OES), (31) mass spectrometry (ICP-MS), (31,32) X-ray fluorescence (XRF), (32) scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDX), (14,20,33) or a combination of methods to obtain complementary information about particle size, morphology, and composition. (31,32) These methods require leaf sampling in the field and can thus only be carried out in relatively low temporal resolution (days to weeks), which is unsuitable to detect the impact of diurnal patterns and related effects of wind speed and PM concentration on deposition and resuspension.
In contrast, the EC technique provides direct measurements of the net surface-atmosphere exchange of gases and particles. (23,34,35) EC can operate at high temporal resolution, thus it is effective to understand flux temporal dynamics. From a spatial point of view, EC requires a homogeneous area that is difficult to meet within the urban context: these areas are typically characterized by different surface roughness (36,37) and limited forested area, with the consequence that results can have a lower resolution and cannot be generalized. (38,39) A single measurement point can integrate an area ranging from hundreds of square meters up to a few square kilometers, resulting in a level of uncertainty that spans from 6% in natural areas (40) to about 12% in urban areas. (39) The combination of measurements at leaf and ecosystem scales enables evaluation on different temporal and spatial resolution, but it has rarely been used to assess PM net exchanges.
In this study, we compared the net PM deposition flux calculated by the i-Tree Eco model with EC assessments within and above a Mediterranean urban forest located in the city of Naples (Italy) to evaluate the dry deposition trend over the day (canopy scale). We then used PM loads on the leaf surface measured by SEM/EDX and VF to validate the accumulation range estimated by the model (leaf scale). Furthermore, a sensitivity analysis was performed to assess the effect of different parameters on the accuracy of model evaluations using a specific deposition velocity for broadleaf trees.
The study aims to provide the first comprehensive and consistent evaluation of model assumptions for PM2.5 removal to properly quantify the contribution of urban trees in removing airborne particulate matter relative to different environmental boundary conditions. Finally, we discussed the pros and cons of the applied techniques and depict model deficits, also suggesting specific future improvements.

Methods

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Study Area

The study area is the Real Bosco di Capodimonte, a Mediterranean urban forest located within the city of Naples, Italy (40.8725° N, 14.2533° E; area = 117.27 km2, population = 944148). Particulate matter pollution is particularly relevant in Italian cities where concentrations are higher than European standards, and the main PM sources are combustion and agriculture. (1) In our study area, the average PM2.5 from 2015 to 2019 was 16.2 μg m–3 and the main sources of particulate matter are traffic, heating, and Saharan dusts (PM10) (Agenzia Regionale per la Protezione Ambientale della Regione Campania, http://www.arpacampania.it). The forest is dominated by Quercus ilex L. with a few large trees of Pinus pinea L. and some open areas of meadows mainly composed of Trifolium L. and Medicago L. The climate is typically Mediterranean, characterized by prolonged dry summer periods and mild winters, with a mean annual temperature of 16.3° and precipitation of 855 mm. (41) At the end of June 2017, a leaf area index (LAI) of 5 was measured using two different LAI 2000 Canopy Analyzers (Li-Cor) in 5 representative areas of the forest, measuring above and below the tree canopy, respectively.

SEM/EDX and Vacuum Filtration Measurements

Wind speed and precipitation data from January to February first, 2017 (day-of-year – DOY- 1–32) were measured at a 10 min resolution with a weather station located in the forest (Osservatorio Meteorologico Università degli Studi di Napoli Federico II, http://www.meteo.unina.it/bosco-di-capodimonte). PM2.5 concentrations in the same days were collected with a hourly resolution by the regional Environmental Agency ARPA Campania in two surrounding urban areas outside the park boundaries: the Astronomical Observatory (NA01:40.863643° N, 14.255496° E, about 400 m southwest) and the National Museum (NA06:40.853679° N, 14.250484° E, about 1.3 Km south).
The sampling of Q. ilex leaves, the dominant species in the park, was carried out on February 1, 2017 at seven different locations inside the forest that were located along the two main wind directions within an area of less than 5 ha. Only previous year leaves were selected (approximated 8 months old). The scanning electron microscope was a Phenom ProX (Phenom-World, The Netherlands) coupled with an X-ray analyzer and a charge-reduction sample holder suited for nonmetalized biological materials. Two leaves were selected from each replicate branch per tree, for a total of 28 leaves (4 per tree) used for SEM/EDX analysis, and a piece of each leaf of about 1 × 1.5 cm2 was fixed with the adaxial surface facing upward to the head of the carbon-based stub (PELCO Tabs, Ted Pella, Inc.).
The size and number of particles size on leaf surfaces were determined by 10 random SEM images for each sample, while EDX allowed us to obtain the elemental composition. With a combination of these data, as described in Baldacchini et al. 2019, (33) the PM2.5 mass per unit leaf area (μg cm–2) was obtained.
For vacuum filtration, ten leaves from each replicate branch per sampling location were selected. Leaf samples were carefully shaken in a flask with 250 mL of deionized water for 5 min and then scanned to measure the leaf surface using ImageJ. The wash water was prefiltered through a 100-μm pore sieve and then dragged, by a vacuum pump, through cellulose filters with a pore size of 10–15 μm measuring the size fraction between 10 and 100 μm, then through filters with a pore size of 2–4 μm measuring the size fraction 2–10 μm, and finally, through nitrocellulose membranes for 0.2 μm measuring the size fraction 0.2–2 μm.
All filters were dried in a moisture-controlled oven for 40 min at 70 °C and placed into the balance room for 30 min for equilibriation of the humidity level, and then mass was measured at the precision of ×10–5 g before (T1) and after (T2) filtration. The applied filter treatment for vacuum filtration measurements of leaf deposited PM upon washing (25) was further tested in terms of reproducibility and standardized based on comparisons with other techniques. (28,31,42) The measured mass of PM deposited on the leaves, per each size fraction, was then estimated per unit of leaf area and divided by the total two-sided leaf area washed (μg cm–2). Only the PM load on the filters with the smaller pore size was used to estimate PM2.5 load. For additional information on the methodology, see Baldacchini et al. (2019) (33) and Ristorini et al. (2020). (31)

Eddy Covariance Assessments

In the summer of the same year from June 13 to September 6 (DOY 164–249), an eddy covariance flux tower conducted measurements at the site. The 26 m height tower was about 4 m higher than the mean tree height. (34) The tower was equipped with a 3-D sonic anemometer (Windmaster Pro, Gill, UK) to measure wind speed and direction. Several fast-response analyzers including an Optical Particle Counter (OPC Multichannel Monitor, FAI Instruments, IT) measured particle sizes from 0.28 to 10 μm at a frequency of 4 Hz and logged data to a CR6 datalogger (Campbell Scientific, USA). Rain was measured with a precipitation sensor (RG100, Environmental Measurements Ltd., UK).
With the EC technique, turbulent fluxes which transport trace gases and other masses are calculated based on measurements of wind speed and compound concentrations. (43)
The basic equation of the flux calculation is
(1)
where the vertical flux (FS) results from the covariance among variations around the average vertical wind speed w′ and the concentration of a scalar of interest s’ over an average period (usually half an hour). A quality control of data was applied discarding fluxes with a quality grade above 3 (0 = best quality data; 9 = worse quality data) (35) and with a friction velocity below 0.2 m s–1 as suggested for the site by Guidolotti et al. (2017). (34) For more detailed information about EC assessments, see Guidolotti et al. (2017) (34) and Pallozzi et al. (2020). (35)

Model Description and Simulation Setup

The PM2.5 deposition flux on the Q. ilex canopy was calculated according to the method used in the i-Tree Eco model (44)
(2)
(3)
(4)
(5)
where ft is the PM2.5 flux at time t (g m–2 s–1), Vdt is the deposition velocity at time t (m s–1), C is the PM2.5 air concentration (g m–3), LAI is the leaf-area index, Rt is the PM2.5 flux resuspended in the atmosphere at time t (g m–2 s–1), At is PM2.5 mass accumulated on leaves at time t (g m–2) depending on previous hour deposition as well as precipitation (At-1), rrt denotes a “resuspension class”, which is the relative amount of deposited PM2.5 that is resuspended at a specific wind speed at time t (%), and Ft is the net PM2.5 removal at time t after considering resuspension. The accumulated PM2.5 on leaves (At) refers to square meters of tree cover and therefore has been rescaled by the LAI to compare it with leaf measurements.
Deposition velocities (vdt) and resuspension classes (rrt) both depend on wind speed and are defined based on the i-Tree Eco model standards. (7,44) When precipitation events are higher than the maximum water storage of the canopy (Ps in mm), which is calculated according to the potential leaf water storage plws (0.2 mm) and LAI (Ps = plws * LAI), all PM2.5 accumulated on leaves is assumed to be washed off and At, Rt, and Ft are set to 0. (44)
Additional simulations have been carried out using the deposition velocities suggested recently by Pace and Grote (2020) (21) for broadleaved trees (vds)
(6)
where w′ (m s–1) is the wind speed at time t.
The sensitivity of the model parametrization was carried out considering a factor of 2 and 3 for the potential leaf water storage, deposition velocity, resuspension classes, and the leaf washing after rainfall events that exceed the maximum water storage of the canopy (Table 1). Furthermore, the combined effect of parameters (combo) with factors 2 and 3 was evaluated. The impact of the parameter variations to deposition and cumulative flux was assessed using a multiple comparison of means (Turkey’s HSD test).
Table 1. Model Parameter Modification to Assess the Deposition Flux Sensitivity
ParameterStandardFactor 2Factor 3
Potential leaf storage0.20.40.6
Deposition velocity0.10940.21880.3282
Resuspension classes1.000.50.33
Leaf washing100%50%33%
Model simulations were performed during two different periods in 2017: DOY 1–32 for the comparison of simulated accumulated deposition with leaf measurements of PM accumulated on leaves (33) (using hourly wind speed, precipitation, and PM2.5 measured at local weather stations as previously described) and DOY 164–249 for the comparison of deposition flux with EC assessments (35) (using half-hour wind speed, precipitation, and PM2.5 measured at the tower).

Results

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PM Concentrations, Wind Speed, and Precipitation

The two periods analyzed showed differences in wind speed, precipitation, and PM2.5 concentrations (Figure 1). In particular, the wind speed recorded from the eddy covariance station (DOY 164–249) is slightly greater due to the height of the tower (26 m) compared to the measurements in winter (DOY 1–32) from the local weather station (≈15 m). Precipitation is considerably lower, and intense rainfall events are much less pronounced during the summer (DOY 164–249) compared to January (DOY 1–32), which is typical of the Mediterranean climate. The particulate matter concentration is also higher during the winter (DOY 1–32) due to residential heating as well as fireworks on the first day of the year. The meteorological data obtained by the two measurement systems (EC tower and the local weather station) have been compared to demonstrate that both could be used to simulate the deposition regime during the period of DOY 164–249 (SI Figure S1–3). For this time period, PM2.5 concentrations are in the same order of magnitude at both places and precipitation events are almost the same. Wind speed data have a similar trend and magnitude, with larger outliers obtained with EC measurements, likely due to the greater height of the tower in comparison with the weather station.

Figure 1

Figure 1. Wind speed, precipitation, and PM2.5 concentration throughout the two measurement campaigns. Particulate matter data are reported for the period DOY 1–32 up to the leaf sampling day (February 1st).

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Model vs PM2.5 Leaf Accumulation

Both the VF and the SEM/EDX methodologies resulted in similar estimates of average PM2.5 mass per unit leaf area (Table 2). The modeled accumulated PM2.5 mass is from 6 to around 20 times lower, based on the i-Tree Eco parametrization (0.4 μg cm–2), and from about 2.2 to 7.2 times lower with the broadleaf specific deposition velocity (1.1 μg cm–2), in comparison to the range of values indicated by the two measurement methods (min = 2.4; max = 7.9 μg cm–2) (Figure 2).
Table 2. PM2.5 Mass Per Unit Leaf Area Measured by SEM/EDX and Vacuum Filtration (VF) on February 1, 2017
PM2.5(μg cm-2)MINMEANMAX
SEM/EDX2.4 ± 0.44.7 ± 1.07.9 ± 1.0
VF3.0 ± 1.04.6 ± 0.86.4 ± 0.2

Figure 2

Figure 2. Modeled cumulative PM2.5 (At) calculated according to the i-Tree Eco standard parametrization (i-Tree) and broadleaf specific deposition velocity (Broadleaf), compared with leaf measurements of the PM2.5 load by SEM/EDX and vacuum filtration (VF), on leaves collected on February 1, 2017 (min = 2.4; max = 7.9 μg cm–2). Precipitation events above the maximum water storage of the canopy (Ps) wash off leaves and set the cumulative flux to 0.

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The SEM/EDX analysis was not able to distinguish coagulated particles from PM10 by automated image grain analysis, and thus the total PM2.5 load value might be underestimated. However, results show a similar average PM2.5 mass with respect to VF (Table 2), where coagulated particles are expected to be disaggregated, confirming the reliability of the methodology for PM accumulation on leaves.
A period of 30 days was considered to evaluate the model deposition calculations up to the leaf sampling date. However, the model’s ability to represent deposition is evaluated for the last week of January only, since according to the model’s internal assumptions, a high-precipitation event on January 23rd completely washed off PM from leaves (Figure 2).

Model vs Eddy Covariance Diurnal Fluxes

The EC in summer (DOY 164–249) indicates an average diurnal flux that is characterized by a small deposition of PM2.5 in the first part of the day until 10 a.m., followed by a high resuspension (release of particles back into the atmosphere) likely caused by the increase in wind speed and a decrease in airborne particle concentration that results in a negative net flux deposition (Figure 3). The higher PM concentration in the morning is related to both increased vehicular traffic during these hours along with an accumulation of pollutants during the night, which results from more stable atmospheric conditions and reduced turbulent exchange. (35)

Figure 3

Figure 3. Top left: Hourly average net flux throughout the day (DOY 1–32) modeled using the i-Tree Eco standard parametrization (i-Tree) and the specific parametrization for broadleaved species (Broadleaf). Bottom left: Hourly average wind speed (ws) and particulate matter concentration (PM2.5) throughout the day during the same period. Top right: Half-hourly average net flux (DOY 164–249) measured by the eddy covariance (EC) and simulated fluxes using either the i-Tree Eco standard parametrization (i-Tree) or the specific parametrization for broadleaved species (Broadleaf). Bottom right: Half-hourly average wind speed (ws) and particulate matter concentration (PM2.5) throughout the day during the same period.

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The modeled flux with the i-Tree Eco parametrization shows the same range of particle deposition as determined by the EC flux, but results are less sensitive to wind speed and particulate matter variations. The maximum deposition rate using the i-Tree Eco parametrization is calculated for midday, when wind speed is highest, which is a bit later than indicated by the measurements. The characteristic of the model to simulate a positive net flux for PM during high wind speed periods despite simultaneously occurring high resuspension rates has already been shown by Pace and Grote 2020 (21), at least as long occasional precipitation events are reducing the accumulated PM load.
Overall, the high resuspension is better reflected by the specific broadleaf-parametrization than the standard one, resulting in an overall better fit to the trend measured with EC.
In comparison to that of summer (DOY 164–249), the simulated daily average particle deposition in winter (DOY 1–32) is much larger, predominantly due to higher pollution concentrations. During winter, resuspension processes are not dominant during any time of the day. This pattern is different in the summer period, where lower pollutant concentration and higher wind speed lead to high (measurements) or moderate (simulations) net resuspension fluxes during midday or early afternoon, respectively. The differences between simulation results and measurements may indicate either a still too small sensitivity of resuspension to wind speed or, more likely, an underestimation of the canopy particle storage (Figure 2), which limits the potential resuspension of particles. (7,21)

Sensitivity Analysis to Model Parametrization

By increasing the deposition velocity (vds) by at least a factor of 2, the PM2.5 accumulation estimated by the model falls within the range measured by SEM/EDX and VF (Figure 4). Model simulations are less sensitive to the variation of other parameters such as plws (potential leaf water storage), rr (resuspension rate), and washing (leaf washing). However, the combined effect of all parameters (combo) results in a better fit to the average of leaf measurements than vds changes alone. In particular, the higher maximum water storage of the canopy (Ps) which depends on plws, the reduced leaf washing after rainfall events (washing), and a lower resuspension rate (rr) allow a larger deposition of PM2.5 on leaves. The multiple comparison of means (Tukey HSD) shows significant differences with the “standard” simulation only for the “washing” and “combo” run (SI Table S1).

Figure 4

Figure 4. Sensitivity analysis of the modeled PM2.5 accumulation on leaves (DOY 1–32) to the deposition velocity (vds), potential leaf water storage (plws), resuspension classes (rr), leaf washing (washing), and combining the different parametrization (combo). The dashed line indicates the leaf PM2.5 load range measured with SEM/EDX and VF collected on February 1, 2017 (min = 2.4; max = 7.9 μg cm–2).

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The high sensitivity of the model to deposition velocity, compared to the other parameters, is also apparent from the comparison of the modeled PM2.5 net flux with the EC assessment (Figure 5). In particular, an increase by a factor of 2 better matches the deposition peaks in the first part of the day as well as the high resuspension rates during the afternoon. Since the sensitivity of net pollution removal to changes of parameters other than vds is very small, the combined effect of all the parameters (combo) is very similar to the effect on vds changes with a slight delay in the negative flux trend due to the lower resuspension rates (rr). The multiple comparison of means (Tukey HSD) shows significant differences with the “standard” simulation only in compariosn with the change in “vds” by a factor of 3 (SI Table S2).

Figure 5

Figure 5. Sensitivity analysis of the modeled PM2.5 net flux to the deposition velocity (vds), potential leaf water storage (plws), resuspension classes (rr), leaf washing (washing), and combining the different parametrization (combo) compared with the eddy covariance flux (DOY 164–249).

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Discussion

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It is known that PM removal from urban trees depends on the morphological properties of the vegetation, the seasonal changes in leaf development, (45) and environmental parameters including PM concentration, wind speed, and precipitation rate. (46,47) The Mediterranean climate is characterized by long periods of summer drought when PM accumulated on the leaves is not washed off by rain but may be exposed to wind resuspension. (48) Here, we show that periods of high resuspension occur, generating a negative net flux, especially in the second part of the day (Figure 3). This pattern was particularly evident when analyzing EC measurements in the summer period (DOY 164–249; Figure 3), compared to the modeled net flux in the winter period (DOY 1–32; Figure 3), where the trend follows the development of wind speed with a higher deposition at mid-day hours. Another EC study of PM deposition on a Q. ilex L. forest in Rome, mainly carried out in summer, also showed the same trend of a high resuspension in the middle of the day. (23) These results have been also confirmed from modeling simulations by Nowak et al. (2013) (7) and Pace and Grote (2020), (21) showing an increase in particle resuspension with increased wind speed. A different seasonal pattern in winter is also visible from the EC assessments carried out in February 2018 at the same site by Pallozzi et al. (2020) (35) where, on the contrary, the deposition mainly occurs in the central hours of the day. Performing a model simulation for the same period and location, we obtained a net flux in the same range as determined in the above-mentioned study (35) (SI Figure S4). In particular, model- and EC results are similar during the deposition phase at midday. However, simulations diverge from measurements for the early and late hours of the day, where the model tends to calculate deposition while net resuspension has been measured with the EC method.
A modeling concept that considers the most important in- and out-flows in mechanistic dependency on wind speed could represent the range of the net removal flux (between −0.1 and +0.1 μg m–2 s–1) and pattern of the measurements, although the high resuspension rates could only be simulated when velocity parameters were considerably larger than originally considered (Figure 3). This finding is, however, to be treated with caution. Since the measured outflow of particles (leading to a negative net removal rate) is considerably high, it can be hypothesized that particles may not only originate from previous leaf deposition but also from other sources (e.g., soil), as the footprint defined by EC is relatively heterogeneous (forest, meadow, building). (34,35) Regarding our EC station, Pallozzi et al. (2020) (35) estimated that on average up to the 80% of the footprint was within the park boundaries at both day and night time.
Only a few studies have investigated the role of urban landscapes on EC fluxes. A specific split footprint approach was implemented for PM by Järvi et al. (2009) (49) in a heterogeneous area of Helsinki, revealing a smaller impact of vegetated areas than of unvegetated ones on PM fluxes. However, a reliable evaluation of the effect of vegetated and nonvegetated areas on fluxes requires the presence of an EC tower network. (37,50) Furthermore, it should be noted that compared to gas exchange, which includes a larger data set of net flux measurements, the high-quality control applied for particles discarded about 60% of the half-hour data, resulting in a less robust data set (35) that did not allow for the comparison of modeled data with the cumulated EC flux data.
Overall, the model calculation, using a specific vd for broadleaf trees based on wind speed (eq 6), performed better compared to the i-Tree Eco parametrization, which uses a specific vd for different wind speed classes. (7) The latter is considerably less sensitive to wind speed, resulting in a smaller deposition flux that is almost offset by resuspension. In effect, the i-Tree parametrization leads to a slightly declining net deposition flux after midday which is not in accordance with measurements (Figure 3). The current parametrization could be improved by increasing the vd (Figures 4, 5). In fact, a higher vd is also supported from other model approaches and experimental measurements. For example, PM2.5 deposition simulations for the city of Leicester (UK), assessed with a Computational Fluid Dynamics model, used a vd of 0.64 cm s–1 which is about 3-fold the value implemented in i-Tree. (11) Sun et al. (2014) (51) also measured an average vd above a deciduous forest in spring of about 1 cm s–1 during the day. An improvement in model parametrization is thus required, in particular with regard to the deposition velocity (SI Figure S5), which allows not only a better estimation of leaf accumulation (Figure 4) but also a better agreement with the net deposition flux (Figure 5).
Another model uncertainty is related to the amount of PM removed by precipitation. Xu et al. (2017) (10) found that PM wash-off rates increase with cumulative precipitation up to a maximum amount of 12.5 mm of rain, removing 51 to 70% of PM accumulated on leaves, with a small amount of PM still retained on the leaf surface. Washing rate varies with precipitation regime and leaf retention properties. (52) PM removal is stronger with low intensity rainfall at smooth leaf surfaces, while rough leaf surfaces release more PM under short-duration, high-intensity events. (53) Smooth and waxy surfaces cannot hold as many particles per unit leaf area as leaves with rough surfaces. (54) Furthermore, leaves with trichomes and wax accumulations at the surface are known to strongly hold on to PM, often keeping a certain percentage of particles, particularly smaller particles, regardless of precipitation intensity. (47,55,56)
In our study, several precipitations events occurred before the leaf sampling (DOY 1–32, Figure 1) and based on the current parametrization in i-Tree Eco (standard) the last event on January 23rd, which was above the maximum canopy water storage (1 mm), washed off all particulate matter from leaves (At = 0) (Figure 2). We therefore hypothesize that the underestimation of PM accumulation by the model, compared with VF and SEM/EDX measurements (Figure 2), may partially result from not considering older particles that are tightly bound to leaves or particles that were on the leaves prior to DOY 1.
The “combo” run in the sensitivity analysis of the model parametrization (Figure 4) showed that by increasing the water storage of the canopy (PS), reducing the percentage of leaf washing after rainfall events above the threshold, as well as reducing the resuspension rate, tree leaves accumulate more PM2.5 and attain values closer to the range measured by leaf analysis. The quantity of particles on the leaves that is transported to the ground by rainfall is important for the estimation of the total amount of PM removed by trees. If we compare the results of the “standard” parametrization, where all the amount of PM accumulated on leaves is washed off by rain events above Ps, with the “combo” run considering a factor 3 where only 33% of PM is removed (Figure 4), the difference in overall PM removal is relatively small (standard = 0.16 g m–2 – combo = 0.21 g m–2). The reason for this minimal difference is that although in the case of standard parametrization 100% of PM is removed in one event, the amount of PM accumulated on the leaves is much lower compared to the “combo” simulation.
Both model parametrizations underestimate the PM that accumulates on the leaves compared to the techniques carried out at leaf level (Figure 2). The VF and SEM/EDX showed a good agreement in the measurement of fine PM load (about 5 μg cm–2 on average, in both cases; Table 2), a value that is in accordance with other experiments on broadleaves (about 5 μg cm–2 (18,26,27,57)). In another study that also used the VF technique, a similar amount of PM2.5 (on average over four sites that represented a rural-urban gradient 4.2 ± 0.8 μg cm–2) was found by VF on leaves of Q. ilex in January, but highest values were recorded in August especially in some sites (on average 13.4 ± 1.9 μg cm–2). (28) These results show that site and weather conditions are important for determining the actual accumulation of PM and that measurements during a specific time-period are not representative for the whole year. However, they may still be of use for the evaluation of model processes as long as driving forces such as weather conditions are correctly considered.
The fraction of particles that accumulates on the leaf surface depends on species-specific properties and increases with the abundance of trichomes, (16,18,58) epicuticular waxes, (15,25,26) and surface roughness. (17) An accumulation index has been recently developed considering a number of leaf properties analyzed with a microscope, which will help to rank the various species and to optimize those planting programs aimed at maximizing PM removal. (14)Q. ilex is a common urban tree in Mediterranean cities, (59,60) and it is an evergreen species with a higher LAI than most other broadleaves, which makes it particularly suitable for the accumulation of particulate matter on leaves (28,61) and less subject to seasonal variation related to leaf development. (45) Thanks to the presence of trichomes and specific leaf area, it was recently classified as one of the most effective particle accumulators of urban plant species. (16) Furthermore, the presence of epicuticular waxes on Q. ilex leaves and a good retention capacity enhance the accumulation of fine particles and the adsorption of lipophilic organic pollutants. (28,61)
All these factors may partially justify the underestimation observed in the model calculation of leaf deposited PM amount (Figure 2). Specific leaf morphological traits may hold PM much tighter, (45,61) demanding more water for washing (10) and decreasing the amount of PM which may resuspend. (62) A tight adherence of particles may result from a larger amount of leaf-encapsulated particle. (45) This is not included in the present model but deserves more interest in future model development.
Although this investigation does not provide an overview about different species responses, it is likely from the current study and literature that a species-specific parametrization could improve the accuracy of model estimates. For example, distinguishing specific deposition velocities for conifers and broadleaves, (21) considering the influence of various foliage traits on resuspension rates (12,63) and leaf washing, (53) could help improve model estimates. Also, the i-Tree Eco model uses a big-leaf approach for PM2.5 estimates and the calculation of PM removal might be improved using a multilayered canopy distribution, (64) which could allow for a distinction of leaves exposed to specific wind speeds and intercepted precipitation. In fact, rainfall and wind intensities vary within the tree canopy, with upper-canopy layers more exposed to rain washing and resuspension of particles by wind in comparison to lower canopy layers.
While several studies across the world focus on improving the estimates of PM removal by urban vegetation, we provide here, for the first time, a comparison of simulated PM2.5 deposition using the methodology implemented in i-Tree Eco, the most commonly used model in urban forestry, (13) with different field measurement techniques of canopies (EC) and leaves (VF and SEM/EDX).
In general, the simulations were able to adequately represent the PM deposition on an urban forest, indicated by similar magnitudes and dynamics as obtained with measurements at different scales (leaf, canopy, forest). However, our sensitivity analysis indicated that the current parametrization of i-Tree Eco is suboptimal for the specific case investigated here. In particular, incorporating the impact of leaf traits that determine parameters of particulate matter accumulation and resuspension, which directly affect the deposition velocity and the leaf washing process, would likely improve model estimates of PM removal by local urban forests.
In addition, longer-term studies with more frequent determination of PM2.5 accumulation would be beneficial to determine potential accumulation limits or a dependence of resuspension from PM storages on leaves. Since the importance of leaf properties is highlighted in the literature, future research should expand the investigation of species-specific leaf impacts on PM vd, wash off, and resuspension rates to aid in model parametrization.

Supporting Information

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The Supporting Information provides additional information on the representativeness of local weather and pollution stations compared to data measured by the EC tower, results of the multiple comparison of accumulated and net flux means (Turkey’s HSD) performing model simulations with a change in parameters, a comparison between the model and EC assessments in February 2018, and the sensitivity analysis of the deposition velocity considering a modification of parameters compared with EC results. The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.0c07679.

  • Figures S1−S5; Tables S1 and S2 (PDF)

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Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

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  • Corresponding Author
  • Authors
    • Rocco Pace - Institute of Research on Terrestrial Ecosystems (IRET), National Research Council (CNR), Porano (TR), 05010, Italy;  Orcidhttp://orcid.org/0000-0002-3126-635X
    • Chiara Baldacchini - Institute of Research on Terrestrial Ecosystems (IRET), National Research Council (CNR), Porano (TR), 05010, Italy;  Biophysics and Nanoscience Centre, Department of Ecological and Biological Sciences (DEB), University of Tuscia, Viterbo, 01100, Italy;  Orcidhttp://orcid.org/0000-0002-5268-6572
    • Emanuele Pallozzi - Institute of Research on Terrestrial Ecosystems (IRET), National Research Council (CNR), Monterotondo Scalo (RM), 00015, Italy
    • Rüdiger Grote - Institute of Meteorology and Climate Research, Atmospheric Environmental Research (IMK-IFU), Karlsruhe Institute of Technology (KIT), Garmisch-Partenkirchen, 82467, Germany
    • David J. Nowak - USDA Forest Service, Northern Research Station, Syracuse, New York 13210, United States
    • Carlo Calfapietra - Institute of Research on Terrestrial Ecosystems (IRET), National Research Council (CNR), Porano (TR), 05010, Italy;  Orcidhttp://orcid.org/0000-0001-5040-4343
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This research was supported by the following projects: “EUFORICC”– Establishing Urban Forest based solutions In Changing Cities (PRIN 20173RRN2S: “Projects of National Interest”), and “ICOS”– Integrated carbon observation system, both founded by the Italian Ministry of Education, University and Research (MIUR). The authors thank Raffaele Viola from the “Osservatorio Meteorologico Università degli Studi di Napoli Federico II” for providing weather data, and Gregorio Sgrigna, Marco Ciolfi, Michele Antonio Salvatore and Francesco De Fino for helpful discussions and suggestions. A special thanks to the Director of Bosco di Capodimonte Sylvain Bellenger and his team for the fruitful collaboration and availability in installing the station within the park. RP also acknowledges the Graduate School for Climate and Environment (GRACE) of the Karlsruhe Institute of Technology (KIT) for support.

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    Muhammad, S.; Wuyts, K.; Samson, R. Atmospheric Net Particle Accumulation on 96 Plant Species with Contrasting Morphological and Anatomical Leaf Characteristics in a Common Garden Experiment. Atmos. Environ. 2019, 202, 328– 344,  DOI: 10.1016/j.atmosenv.2019.01.015
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    Atmospheric net particle accumulation on 96 plant species with contrasting morphological and anatomical leaf characteristics in a common garden experiment
    Muhammad, S.; Wuyts, K.; Samson, R.
    Atmospheric Environment (2019), 202 (), 328-344CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
    In this study, we investigated leaves of 96 perennial urban plant species consisting of 43 deciduous broadleaf trees, 32 deciduous broadleaf shrubs, 14 deciduous and evergreen needle/scale-like, 5 evergreen broadleaves, and 2 climber species for their differences in net particle accumulation. Leaf satn. isothermal remanent magnetization (SIRM), a proxy for traffic and industry induced particle accumulation, along with morphol. and anatomical leaf traits were analyzed in a common garden expt. in June and Sept. 2016. Leaf SIRM varied significantly between plant species. The most effective net particle accumulating plant species with a median value of 23.0μA were Buddleja davidii, Viburnum opulus, Carpinus betulus, Quercus ilex, Viburnum lantana, Rosa rugosa, Sorbus aria, Aesculus hippocastanum, Pseudotsuga menziesii, Acer campestre. The least effective net particle accumulating plant species with a median value of 10.4μA were Populus alba, Alnus glutinosa, Larix kaempferi, Larix decidua, Plantanus x acerilifolia, Acer pseudoplatanus, Robinia pseudoacacia, Quercus palustris, Rosa canina, Liquidambar styraciflua. The "variable importance" in net particle accumulation for the investigated plant species was achieved using randomForest. The presence of leaf trichomes and specific leaf area were identified as important leaf traits for categorization of the selected plant species in low, medium, and high net particle accumulators.
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    Shao, F.; Wang, L.; Sun, F.; Li, G.; Yu, L.; Wang, Y.; Zeng, X.; Yan, H.; Dong, L.; Bao, Z. Study on Different Particulate Matter Retention Capacities of the Leaf Surfaces of Eight Common Garden Plants in Hangzhou, China. Sci. Total Environ. 2019, 652, 939– 951,  DOI: 10.1016/j.scitotenv.2018.10.182
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    Study on different particulate matter retention capacities of the leaf surfaces of eight common garden plants in Hangzhou, China
    Shao Feng; Wang Lihua; Li Guo; Yu Lu; Wang Yujie; Zeng Xinru; Yan Hai; Sun Fengbin; Dong Li; Bao Zhiyi
    The Science of the total environment (2019), 652 (), 939-951 ISSN:.
    The severity of inhalable particulate matter (PM) pollution in the atmosphere is increasing; however, plants can effectively reduce the concentration of atmospheric PM by retaining it on their leaves. In this paper, eight common garden plants in Hangzhou, China, were selected as the study objects to observe the morphological features of the leaf surfaces and the retained particles and to analyze the elemental composition of the particles. Confocal laser scanning microscopy (CLSM) was performed to detect the morphological features of the leaf surfaces, and the relationship between the roughness of the leaf surface and the number of the retained particulates was quantitatively analyzed. In addition, the elements in the soil were measured via inductively coupled plasma-optical emission spectrometry (ICP-OES) to locate the possible particulate sources. The results revealed that leaves are able to retain particulates via the synergy of multiple microstructures on the leaf surface, such as grooves, folds, small chambers, flocculus projections, long villi, pubescent hairs and waxes. Moreover, the leaf surface roughness is closely related to the number of retained particulates, with rougher surfaces corresponding to more rugged folds and grooves and a stronger retention ability. The retained particulates are primarily composed of C, O, Si, Al, Ca, K, Mg, Nb, Fe, Na and Ti, and a comparison with the elements in the soil samples indicated that these elements originated from soil dust. Among the different particle sizes, PM with a diameter <2.5 μm (PM2.5) presented the greatest retention on the surfaces of the different plant leaves, while a much smaller amount of PM with a diameter larger than 10 μm was retained. The research results provide an important theoretical scientific basis for the mechanism underlying PM adsorption by plants and strategies for the reasonable selection of garden dust-retaining tree species.
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    Chen, L.; Liu, C.; Zhang, L.; Zou, R.; Zhang, Z. Variation in Tree Species Ability to Capture and Retain Airborne Fine Particulate Matter (PM2.5). Sci. Rep. 2017, 7 (1), 1– 11,  DOI: 10.1038/s41598-017-03360-1
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    Erratum: Reduced GABAergic transmission in the ventrobasal thalamus contributes to thermal hyperalgesia in chronic inflammatory pain
    Zhang, Chan; Chen, Rong-Xiang; Zhang, Yu; Wang, Jie; Liu, Feng-Yu; Cai, Jie; Liao, Fei-Fei; Xu, Fu-Qiang; Yi, Ming; Wan, You
    Scientific Reports (2017), 7 (1), 1-6CODEN: SRCEC3; ISSN:2045-2322. (Nature Research)
    Scientific Reports 7: Article no.: 41439; published online: 02 Feb. 2017; updated: 04 May 2017 This Article contains errors in Figures 1, 2, 3, 4, 5, 6, 7 and 8. In Figure 1, n = 7 was omitted from panel C. In Figure 2, labels are missing from the bars of panel B. In Figure 3, 'Control' was incorrectly given as 'Sham', labels are missing from the bars in Figure 3B and C, and n = 7 and n = 9 were omitted from Figure 3E.
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    Räsänen, J. V.; Holopainen, T.; Joutsensaari, J.; Ndam, C.; Pasanen, P.; Rinnan, Å.; Kivimäenpää, M. Effects of Species-Specific Leaf Characteristics and Reduced Water Availability on Fine Particle Capture Efficiency of Trees. Environ. Pollut. 2013, 183, 64– 70,  DOI: 10.1016/j.envpol.2013.05.015
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    19
    Effects of species-specific leaf characteristics and reduced water availability on fine particle capture efficiency of trees
    Rasanen, Janne V.; Holopainen, Toini; Joutsensaari, Jorma; Ndam, Collins; Pasanen, Pertti; Rinnan, Asmund; Kivimaenpaa, Minna
    Environmental Pollution (Oxford, United Kingdom) (2013), 183 (), 64-70CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
    Trees can improve air quality by capturing particles in their foliage. We detd. the particle capture efficiencies of coniferous Pinus sylvestris and three broadleaved species: Betula pendula, Betula pubescens and Tilia vulgaris in a wind tunnel using NaCl particles. The importance of leaf surface structure, physiol. and moderate soil drought on the particle capture efficiencies of the trees were detd. The results confirm earlier findings of more efficient particle capture by conifers compared to broadleaved plants. The particle capture efficiency of P. sylvestris (0.21%) was significantly higher than those of B. pubescens, T. vulgaris and B. pendula (0.083%, 0.047%, 0.043%, resp.). The small leaf size of P. sylvestris was the major characteristic that increased particle capture. Among the broadleaved species, low leaf wettability, low stomatal d. and leaf hairiness increased particle capture. Moderate soil drought tended to increase particle capture efficiency of P. sylvestris.
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    Weerakkody, U.; Dover, J. W.; Mitchell, P.; Reiling, K. Quantification of the Traffic-Generated Particulate Matter Capture by Plant Species in a Living Wall and Evaluation of the Important Leaf Characteristics. Sci. Total Environ. 2018, 635, 1012– 1024,  DOI: 10.1016/j.scitotenv.2018.04.106
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    20
    Quantification of the traffic-generated particulate matter capture by plant species in a living wall and evaluation of the important leaf characteristics
    Weerakkody, Udeshika; Dover, John W.; Mitchell, Paul; Reiling, Kevin
    Science of the Total Environment (2018), 635 (), 1012-1024CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
    Traffic-generated particulate matter (PM) is a significant fraction of urban PM pollution and little is known about the use of living walls as a short-term strategy to reduce this pollution. The present study evaluated the potential of twenty living wall plants to reduce traffic-based PM using a living wall system located along a busy road in Stoke-on-Trent, UK. An Environmental Scanning Electron Microscope (ESEM) and ImageJ software were employed to quantify PM accumulation on leaves (PM1, PM2.5 and PM10) and their elemental compn. was detd. using Energy Dispersive X-ray (EDX). Inter-species variation in leaf-PM accumulation was evaluated using a Generalized Linear Mixed-effect Model (GLMM) using time as a factor; any differential PM accumulation due to specific leaf characteristics (stomatal d., hair/trichomes, ridges and grooves) was identified. The study showed a promising potential for living wall plants to remove atm. PM; an estd. av. no. of 122.08 ± 6.9 × 107 PM1, 8.24 ± 0.72 × 107 PM2.5 and 4.45 ± 0.33 × 107 PM10 were captured on 100 cm2 of the living wall used in this study. Different species captured significantly different quantities of all particle sizes; the highest amt. of all particle sizes was found on the leaf-needles of Juniperus chinensis L., followed by smaller-leaved species. In the absence of an apparent pattern in correlation between PM accumulation and leaf surface characteristics, the study highlighted the importance of individual leaf size in PM capture irresp. of their variable micro-morphol. The elemental compn. of the captured particles showed a strong correlation with traffic-based PM and a wide range of important heavy metals. We conclude that the use of living walls that consist largely of smaller-leaved species and conifers can potentially have a significant impact in ameliorating air quality by removing traffic-generated PM pollution to improve the wellbeing of urban dwellers.
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    Pace, R.; Grote, R. Deposition and Resuspension Mechanisms Into and From Tree Canopies: A Study Modeling Particle Removal of Conifers and Broadleaves in Different Cities. Front. For. Glob. Chang. 2020, 3 (March), 26,  DOI: 10.3389/ffgc.2020.00026
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    Hofman, J.; Samson, R. Biomagnetic Monitoring as a Validation Tool for Local Air Quality Models: A Case Study for an Urban Street Canyon. Environ. Int. 2014, 70 (2014), 50– 61,  DOI: 10.1016/j.envint.2014.05.007
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    Biomagnetic monitoring as a validation tool for local air quality models: a case study for an urban street canyon
    Hofman Jelle; Samson Roeland
    Environment international (2014), 70 (), 50-61 ISSN:.
    Biomagnetic monitoring of tree leaf deposited particles has proven to be a good indicator of the ambient particulate concentration. The objective of this study is to apply this method to validate a local-scale air quality model (ENVI-met), using 96 tree crown sampling locations in a typical urban street canyon. To the best of our knowledge, the application of biomagnetic monitoring for the validation of pollutant dispersion modeling is hereby presented for the first time. Quantitative ENVI-met validation showed significant correlations between modeled and measured results throughout the entire in-leaf period. ENVI-met performed much better at the first half of the street canyon close to the ring road (r=0.58-0.79, RMSE=44-49%), compared to second part (r=0.58-0.64, RMSE=74-102%). The spatial model behavior was evaluated by testing effects of height, azimuthal position, tree position and distance from the main pollution source on the obtained model results and magnetic measurements. Our results demonstrate that biomagnetic monitoring seems to be a valuable method to evaluate the performance of air quality models. Due to the high spatial and temporal resolution of this technique, biomagnetic monitoring can be applied anywhere in the city (where urban green is present) to evaluate model performance at different spatial scales.
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    Fares, S.; Savi, F.; Fusaro, L.; Conte, A.; Salvatori, E.; Aromolo, R.; Manes, F. Particle Deposition in a Peri-Urban Mediterranean Forest. Environ. Pollut. 2016, 218, 1278– 1286,  DOI: 10.1016/j.envpol.2016.08.086
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    Particle deposition in a peri-urban Mediterranean forest
    Fares, Silvano; Savi, Flavia; Fusaro, Lina; Conte, Adriano; Salvatori, Elisabetta; Aromolo, Rita; Manes, Fausto
    Environmental Pollution (Oxford, United Kingdom) (2016), 218 (), 1278-1286CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
    Urban and peri-urban forests provide a multitude of Ecosystem Services to the citizens. While the capacity of removing carbon dioxide and gaseous compds. from the atm. has been tested, their capacity to sequestrate particles (PM) has been poorly investigated. Mediterranean forest ecosystems are often located nearby or inside large urban areas. This is the case of the city of Rome, Italy, which hosts several urban parks and is surrounded by forested areas. In particular, the Presidential Estate of Castelporziano is a 6000 ha forested area located between the Tyrrhenian coast and the city (25 km downtown of Rome). Under the hypothesis that forests can ameliorate air quality thanks to particle deposition, we measured fluxes of PM1, 2.5 and 10 with fast optical sensors and eddy covariance technique. We found that PM1 is mainly deposited during the central hours of the day, while negligible fluxes were obsd. for PM 2.5 and 10. A Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT v4) simulated PM emission from traffic areas in the city of Rome and showed that a significant portion of PM is removed by vegetation in the days when the plume trajectory meets the urban forest.
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    Fares, S.; Alivernini, A.; Conte, A.; Maggi, F. Ozone and Particle Fluxes in a Mediterranean Forest Predicted by the AIRTREE Model. Sci. Total Environ. 2019, 682, 494– 504,  DOI: 10.1016/j.scitotenv.2019.05.109
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    Ozone and particle fluxes in a Mediterranean forest predicted by the AIRTREE model
    Fares, Silvano; Alivernini, Alessandro; Conte, Adriano; Maggi, Federico
    Science of the Total Environment (2019), 682 (), 494-504CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
    Mediterranean forests are among the most threatened ecosystems from the concurrent effects of climate change and air pollution. This work parameterized the AIRTREE multi-layer model to predict CO2, water, O3, and fine particle exchanges between leaves and the atm. AIRTREE consists of four different modules: canopy environmental module which dets. leaf temp. and radiative fluxes at different levels from above to the bottom of the canopy; a hydrol. module which predicts soil water flow and water availability to plant photosynthetic app.; a photosynthesis module which ests. the net photosynthesis and stomatal conductance; and a deposition module which ests. O3 and PM deposition sinks as a function of gas diffusion resistance in the atm. and within the canopy and leaf boundary layer. AIRTREE model framework, accuracy, and sensitivity are described by comparing modeling results against long-term continuous eddy covariance O3, water, and CO2 flux measurements in a Mediterranean Holm oak forest. Potential use of AIRTREE for O3 risk assessment in relation to the availability of a large observational database from ecosystems distributed worldwide is also discussed.
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    Dzierzanowski, K.; Popek, R.; Gawrońska, H.; Saebø, A.; Gawroński, S. W. Deposition of Particulate Matter of Different Size Fractions on Leaf Surfaces and in Waxes of Urban Forest Species. Int. J. Phytorem. 2011, 13 (10), 1037– 1046,  DOI: 10.1080/15226514.2011.552929
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    25
    Deposition of Particulate Matter of Different Size Fractions on Leaf Surfaces and in Waxes of Urban Forest Species
    Dzierzanowski, Kajetan; Popek, Robert; Gawronska, Helena; Saebo, Arne; Gawronski, Stanislaw W.
    International Journal of Phytoremediation (2011), 13 (10), 1037-1046CODEN: IJPHFG; ISSN:1522-6514. (Taylor & Francis, Inc.)
    Particulate matter (PM) is an air contaminant in urban and industrial areas that often exceeds limit values, creating serious problems due to its harmful effects on health. Planting trees and shrubs as air filters is a way to improve air quality in these areas. However, further knowledge on species effectiveness in air purifn. is essential. This study compared four species of tree (Acer campestre L., Fraxinus excelsior L., Platanus × hispanica Mill. ex Muenchh. 'Acerifolia', Tilia cordata Mill.), three species of shrub (Forsythia × intermedia Zabel, Physocarpus opulifolius (L.) Maxim., Spiraea japonica L.), and one climber species (Hedera helix L.) that are commonly cultivated along streets in Poland to capture fine, coarse and larger particles from air. Sep. gravimetric analyses were performed to quantify PM deposited on surfaces and trapped in waxes. Significant differences were found between the plant species tested. The distribution of different particle size fractions differed between and within species and also between leaf surfaces and in waxes.
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    Sæbø, A.; Popek, R.; Nawrot, B.; Hanslin, H. M.; Gawronska, H.; Gawronski, S. W. Plant Species Differences in Particulate Matter Accumulation on Leaf Surfaces. Sci. Total Environ. 2012, 427–428, 347– 354,  DOI: 10.1016/j.scitotenv.2012.03.084
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    Plant species differences in particulate matter accumulation on leaf surfaces
    Saebo A; Popek R; Nawrot B; Hanslin H M; Gawronska H; Gawronski S W
    The Science of the total environment (2012), 427-428 (), 347-54 ISSN:.
    Particulate matter (PM) accumulation on leaves of 22 trees and 25 shrubs was examined in test fields in Norway and Poland. Leaf PM in different particle size fractions (PM(10), PM(2.5), PM(0.2)) differed among the species, by 10- to 15-folds at both test sites. Pinus mugo and Pinus sylvestris, Taxus media and Taxus baccata, Stephanandra incisa and Betula pendula were efficient species in capturing PM. Less efficient species were Acer platanoides, Prunus avium and Tilia cordata. Differences among species within the same genus were also observed. Important traits for PM accumulation were leaf properties such as hair and wax cover. The ranking presented in terms of capturing PM can be used to select species for air pollution removal in urban areas. Efficient plant species and planting designs that can shield vulnerable areas in urban settings from polluting traffic etc. can be used to decrease human exposure to anthropogenic pollutants.
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    Mo, L.; Ma, Z.; Xu, Y.; Sun, F.; Lun, X.; Liu, X.; Chen, J.; Yu, X. Assessing the Capacity of Plant Species to Accumulate Particulate Matter in Beijing, China. PLoS One 2015, 10 (10), e0140664– 18,  DOI: 10.1371/journal.pone.0140664
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    Assessing the capacity of plant species to accumulate particulate matter in Beijing, China
    Mo, Li; Ma, Zeyu; Xu, Yansen; Sun, Fengbin; Lun, Xiaoxiu; Liu, Xuhui; Chen, Jungang; Yu, Xinxiao
    PLoS One (2015), 10 (10), e0140664/1-e0140664/18CODEN: POLNCL; ISSN:1932-6203. (Public Library of Science)
    Air pollution causes serious problems in spring in northern China; therefore, studying the ability of different plants to accumulate particulate matter (PM) at the beginning of the growing season may benefit urban planners in their attempts to control air pollution. This study evaluated deposits of PM on the leaves and in the wax layer of 35 species (11 shrubs, 24 trees) in Beijing, China. Differences in the accumulation of PM were obsd. between species. Cephalotaxus sinensis, Euonymus japonicus, Broussonetia papyriferar, Koelreuteria paniculata and Quercus variabilis were all efficient in capturing small particles. The plants exhibiting high amts. of total PM accumulation (on leaf surfaces and/or in the wax layer), also showed comparatively high levels of PM accumulation across all particle sizes. A comparison of shrubs and trees did not reveal obvious differences in their ability to accumulate particles based on growth form; a combination of plantings with different growth forms can efficiently reduce airborne PM concns. near the ground. To test the relationships between leaf traits and PM accumulation, leaf samples of selected species were obsd. using a scanning electron microscope. Growth forms with greater amts. of pubescence and increased roughness supported PM accumulation; the adaxial leaf surfaces collected more particles than the abaxial surfaces. The results of this study may inform the selection of species for urban green areas where the goal is to capture air pollutants and mitigate the adverse effects of air pollution on human health.
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    Sgrigna, G.; Sæbø, A.; Gawronski, S.; Popek, R.; Calfapietra, C. Particulate Matter Deposition on Quercus Ilex Leaves in an Industrial City of Central Italy. Environ. Pollut. 2015, 197, 187– 194,  DOI: 10.1016/j.envpol.2014.11.030
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    28
    Particulate Matter deposition on Quercus ilex leaves in an industrial city of central Italy
    Sgrigna, G.; Saeboe, A.; Gawronski, S.; Popek, R.; Calfapietra, C.
    Environmental Pollution (Oxford, United Kingdom) (2015), 197 (), 187-194CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
    A no. of studies have focused on urban trees to understand their mitigation capacity of air pollution. In this study particulate matter (PM) deposition on Quercus ilex leaves was quant. analyzed in four districts of the City of Terni (Italy) for three periods of the year. Fine (between 0.2 and 2.5 μm) and Large (between 2.5 and 10 μm) PM fractions were analyzed. Mean PM deposition value on Quercusilex leaves was 20.6 μg cm-2. Variations in PM deposition correlated with distance to main roads and downwind position relatively to industrial area. Epicuticular waxes were measured and related to accumulated PM. For Fine PM deposited in waxes we obsd. a higher value (40% of total Fine PM) than Large PM (4% of total Large PM). Results from this study allow to increase our understanding about air pollution interactions with urban vegetation and could be hopefully taken into account when guidelines for local urban green management are realized.
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    De Nicola, F.; Maisto, G.; Prati, M. V.; Alfani, A. Leaf Accumulation of Trace Elements and Polycyclic Aromatic Hydrocarbons (PAHs) in Quercus Ilex L. Environ. Pollut. 2008, 153 (2), 376– 383,  DOI: 10.1016/j.envpol.2007.08.008
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    29
    Leaf accumulation of trace elements and polycyclic aromatic hydrocarbons (PAHs) in Quercus ilex L.
    De Nicola, F.; Maisto, G.; Prati, M. V.; Alfani, A.
    Environmental Pollution (Amsterdam, Netherlands) (2008), 153 (2), 376-383CODEN: ENPOEK; ISSN:0269-7491. (Elsevier B.V.)
    Quercus ilex L. leaves were collected 4 times in 1 yr at 6 urban sites and 1 remote area to det. trace element and PAH accumulation through concomitant analyses of unwashed and water-washed leaves. Both unwashed and washed leaves showed the highest amts. of trace elements and PAHs in the urban area. Unwashed leaves showed greater differences between urban and remote areas and among the urban sites than washed leaves for trace element and PAH concns. Water-washing resulted in a significant (P <0.001) decrease in leaf concns. of Cr, Cu, Fe, Pb, V, and Zn. By contrast, Cd and total PAH concns. showed no differences between unwashed and washed leaves.
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    Sawidis, T.; Breuste, J.; Mitrovic, M.; Pavlovic, P.; Tsigaridas, K. Trees as Bioindicator of Heavy Metal Pollution in Three European Cities. Environ. Pollut. 2011, 159 (12), 3560– 3570,  DOI: 10.1016/j.envpol.2011.08.008
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    Trees as bioindicator of heavy metal pollution in three European cities
    Sawidis, T.; Breuste, J.; Mitrovic, M.; Pavlovic, P.; Tsigaridas, K.
    Environmental Pollution (Oxford, United Kingdom) (2011), 159 (12), 3560-3570CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
    Concns. of four heavy metals were detd. in tree leaves and bark collected from polluted and non-polluted areas of three European cities (Salzburg, Belgrade and Thessaloniki) for a comparative study. Platanus orientalis L. and Pinus nigra Arn., widespread in urban northern and southern Europe, were tested for their suitability for air quality biomonitoring. Leaves and barks were collected uniformly of an initial quantity of about 30 g of each sample. Anal. was accomplished by electrothermal at. absorption spectrometry after total digestion. Site-dependent variations were found with the highest concn. level measured in Belgrade, followed by Thessaloniki and Salzburg. A higher accumulation of heavy metals was found in bark compared to leaves. Pine tree bark, accumulating higher concns. of trace metals compared to plane tree bark, shows a higher efficiency as bioindicator for urban pollution. Both indicator species are suitable for comparative studies on bioindication of urban air pollution. Oriental plane (Platanus orientalis L.) and Austrian pine (Pinus nigra Arn.), widespread in urban northern and southern Europe, are suitable for comparative biomonitoring of urban air pollution.
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  31. 31
    Ristorini, M.; Baldacchini, C.; Massimi, L.; Sgrigna, G.; Calfapietra, C. Innovative Characterization of Particulate Matter Deposited on Urban Vegetation Leaves through the Application of a Chemical Fractionation Procedure. Int. J. Environ. Res. Public Health 2020, 17 (16), 5717– 19,  DOI: 10.3390/ijerph17165717
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    Innovative characterization of particulate matter deposited on urban vegetation leaves through the application of a chemical fractionation procedure
    Ristorini, Martina; Baldacchini, Chiara; Massimi, Lorenzo; Sgrigna, Gregorio; Calfapietra, Carlo
    International Journal of Environmental Research and Public Health (2020), 17 (16), 5717CODEN: IJERGQ; ISSN:1660-4601. (MDPI AG)
    In this study, we have evaluated the efficiency of a chem. fractionation procedure for the characterization of both the water-sol. and the insol. fraction of the main elemental components of particulate matter (PM) deposited on urban leaves. The proposed anal. approach is based on the chem. anal. of leaf washing solns. and membrane filters used for their filtration. The ionic concn. of leaf washing solns. was compared with their elec. cond., making it a valuable proxy for the quantification of the water-sol. and ionic fraction of leaf deposited PM. The chem. compn. of both the water-sol. and the insol. fraction of PM, resulting from this fractionation procedure, was compared with results obtained by SEM coupled with energy-dispersed X-Rays spectroscopy (SEM/EDX) and processed through chemometrics. Results obtained proved that the proposed approach is able to provide an estn. of total leaf deposited PM and it is highly reliable for the evaluation of the emission impact of different PM sources, being able to increase the selectivity of PM elemental components as specific source tracers; consequently providing useful information also for the assessment of human health risks.
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    Castanheiro, A.; Hofman, J.; Nuyts, G.; Joosen, S.; Spassov, S.; Blust, R.; Lenaerts, S.; De Wael, K.; Samson, R. Leaf Accumulation of Atmospheric Dust: Biomagnetic, Morphological and Elemental Evaluation Using SEM, ED-XRF and HR-ICP-MS. Atmos. Environ. 2020, 221, 117082,  DOI: 10.1016/j.atmosenv.2019.117082
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    Leaf accumulation of atmospheric dust: Biomagnetic, morphological and elemental evaluation using SEM, ED-XRF and HR-ICP-MS
    Castanheiro, Ana; Hofman, Jelle; Nuyts, Gert; Joosen, Steven; Spassov, Simo; Blust, Ronny; Lenaerts, Silvia; De Wael, Karolien; Samson, Roeland
    Atmospheric Environment (2020), 221 (), 117082CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
    Atm. dust deposition on plants enables the collection of site-specific particulate matter (PM). Knowing the morphol. and compn. of PM aids in disclosing their emitting sources as well as the assocd. human health risk. Therefore, this study aimed for a leaf-level holistic anal. of dust accumulation on plant leaves. Plant species (ivy and strawberry) with distinct leaf macro- and micro-morphol. were exposed during 3 mo at a moderate road traffic site in Antwerp, Belgium. Leaves collected every three weeks were analyzed for their magnetic signature, morphol. and elemental content, by a combination of techniques (biomagnetic analyses, ED-XRF, HR-ICP-MS, SEM). Dust accumulation on the leaves was obsd. both visually (SEM) and magnetically, while the metal enrichment was limited (only evident for Cr) and more variable over time. Temporal dynamics during the second half of the exposure period, due to pptn. events and redn. of atm. pollution input, were evidenced in our results (elements/magnetically/SEM). Ivy accumulated more dust than strawberry leaves and seemed less susceptible to wash-off, even though strawberry leaves contain trichomes and a rugged micromorphol., leaf traits considered to be important for capturing PM. The magnetic enrichment (in small-grained, SD/PSD magnetite particles), on the other hand, was not species-specific, indicating a common contributing source. Variations in pollution contributions, meteorol. phenomena, leaf traits, particle deposition (and encapsulation) vs. micronutrients depletion, are discussed in light of the conducted monitoring campaign. Although not completely elucidative, the complex, multifactorial process of leaf dust accumulation can better be understood through a combination of techniques.
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    Baldacchini, C.; Sgrigna, G.; Clarke, W.; Tallis, M.; Calfapietra, C. An Ultra-Spatially Resolved Method to Quali-Quantitative Monitor Particulate Matter in Urban Environment. Environ. Sci. Pollut. Res. 2019, 26 (18), 18719– 18729,  DOI: 10.1007/s11356-019-05160-8
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    An ultra-spatially resolved method to quali-quantitative monitor particulate matter in urban environment
    Baldacchini, Chiara; Sgrigna, Gregorio; Clarke, Woody; Tallis, Matthew; Calfapietra, Carlo
    Environmental Science and Pollution Research (2019), 26 (18), 18719-18729CODEN: ESPLEC; ISSN:0944-1344. (Springer)
    Monitoring the amt. and compn. of airborne particulate matter (PM) in the urban environment is a crucial aspect to guarantee citizen health. To focus the action of stakeholders in limiting air pollution, fast and highly spatially resolved methods for monitoring PM are required. Recently, the trees' capability in capturing PM inspired the development of several methods intended to use trees as biomonitors; this results in the potential of having an ultra-spatially resolved network of low-cost PM monitoring stations throughout cities, without the needing of on-site stations. Within this context, we propose a fast and reliable method to qual. and quant. characterize the PM present in urban air based on the anal. of tree leaves by SEM combined with X-ray spectroscopy (SEM/EDX). We have tested our method in the Real Bosco di Capodimonte urban park (Naples, Italy), by collecting leaves from Quercus ilex trees along transects parallel to the main wind directions. The coarse (PM10-2.5) and fine (PM2.5) amts. obtained per unit leaf area have been validated by weighting the PM washed from leaves belonging to the same sample sets. PM size distribution and elemental compn. match appropriately with the known pollution sources in the sample sites (i.e., traffic and marine aerosol). The proposed methodol. will then allow the use of the urban forest as an ultra-spatially resolved PM monitoring network, also supporting the work of urban green planners and stakeholders.
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    Guidolotti, G.; Calfapietra, C.; Pallozzi, E.; De Simoni, G.; Esposito, R.; Mattioni, M.; Nicolini, G.; Matteucci, G.; Brugnoli, E. Promoting the Potential of Flux-Measuring Stations in Urban Parks: An Innovative Case Study in Naples, Italy. Agric. For. Meteorol. 2017, 233, 153– 162,  DOI: 10.1016/j.agrformet.2016.11.004
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    Pallozzi, E.; Guidolotti, G.; Mattioni, M.; Calfapietra, C. Particulate Matter Concentrations and Fluxes within an Urban Park in Naples. Environ. Pollut. 2020, 266, 115134,  DOI: 10.1016/j.envpol.2020.115134
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    Particulate matter concentrations and fluxes within an urban park in Naples
    Pallozzi, E.; Guidolotti, G.; Mattioni, M.; Calfapietra, C.
    Environmental Pollution (Oxford, United Kingdom) (2020), 266 (Part_3), 115134CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
    Airborne particulate matter can represent a serious issue for human health, esp. in densely populated urban areas. Moreover, the inhalation of particulate can be more harmful with decreasing particles diam. Vegetation can provide many ecosystem services to the citizens, including the removal of many different pollutants in the air, but while the effect on many gaseous compds. has already been widely proved, the capability of particulate matter (PM) sequestration driven by vegetation and its resulting benefit on air quality has not been deeply investigated yet at larger spatial scale, esp. in Mediterranean environment. This study was conducted in the Real Bosco di Capodimonte, a green area of about 125 ha located inside the urban area of Naples (Italy) contg. different species typical of the Mediterranean forest ecosystem. To better understand the interaction between PM and the park area, we measured fluxes of PM10, PM2.5 and PM1 with a fast acquisition analyzer, according to the Eddy Covariance technique. We found that the particle deposition was higher during the central hours of the day and it was more evident for smaller size particles. Furthermore, the daily PM fluxes found accorded with evapotranspiration and carbon sequestration operated by plants, suggesting a possible active role of vegetation on the particulate deposition.
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    Christen, A. Atmospheric Measurement Techniques to Quantify Greenhouse Gas Emissions from Cities. Urban Clim. 2014, 10 (P2), 241– 260,  DOI: 10.1016/j.uclim.2014.04.006
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    Ward, H. C.; Kotthaus, S.; Grimmond, C. S. B.; Bjorkegren, A.; Wilkinson, M.; Morrison, W. T. J.; Evans, J. G.; Morison, J. I. L.; Iamarino, M. Effects of Urban Density on Carbon Dioxide Exchanges: Observations of Dense Urban, Suburban and Woodland Areas of Southern England. Environ. Pollut. 2015, 198, 186– 200,  DOI: 10.1016/j.envpol.2014.12.031
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    Effects of urban density on carbon dioxide exchanges: Observations of dense urban, suburban and woodland areas of southern England
    Ward, H. C.; Kotthaus, S.; Grimmond, C. S. B.; Bjorkegren, A.; Wilkinson, M.; Morrison, W. T. J.; Evans, J. G.; Morison, J. I. L.; Iamarino, M.
    Environmental Pollution (Oxford, United Kingdom) (2015), 198 (), 186-200CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
    Anthropogenic and biogenic controls on the surface-atm. exchange of CO2 are explored for three different environments. Similarities are seen between suburban and woodland sites during summer, when photosynthesis and respiration det. the diurnal pattern of the CO2 flux. In winter, emissions from human activities dominate urban and suburban fluxes; building emissions increase during cold weather, while traffic is a major component of CO2 emissions all year round. Obsd. CO2 fluxes reflect diurnal traffic patterns (busy throughout the day (urban); rush-hour peaks (suburban)) and vary between working days and non-working days, except at the woodland site. Suburban vegetation offsets some anthropogenic emissions, but 24-h CO2 fluxes are usually pos. even during summer. Observations are compared to estd. emissions from simple models and inventories. Annual CO2 exchanges are significantly different between sites, demonstrating the impacts of increasing urban d. (and decreasing vegetation fraction) on the CO2 flux to the atm.
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    Rannik, U.; Aubinet, M.; Kurbanmuradov, O.; Sabelfeld, K. K.; Markkanen, T.; Vesala, T. Footprint Analysis for Measurements over a Heterogeneous Forest. Boundary-Layer Meteorol. 2000, 97 (1), 137– 166,  DOI: 10.1023/A:1002702810929
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    Järvi, L.; Rannik, U.; Kokkonen, T. V.; Kurppa, M.; Karppinen, A.; Kouznetsov, R. D.; Rantala, P.; Vesala, T.; Wood, C. R. Uncertainty of Eddy Covariance Flux Measurements over an Urban Area Based on Two Towers. Atmos. Meas. Tech. 2018, 11 (10), 5421– 5438,  DOI: 10.5194/amt-11-5421-2018
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    Uncertainty of eddy covariance flux measurements over an urban area based on two towers
    Jarvi, Leena; Rannik, Ullar; Kokkonen, Tom V.; Kurppa, Mona; Karppinen, Ari; Kouznetsov, Rostislav D.; Rantala, Pekka; Vesala, Timo; Wood, Curtis R.
    Atmospheric Measurement Techniques (2018), 11 (10), 5421-5438CODEN: AMTTC2; ISSN:1867-8548. (Copernicus Publications)
    The eddy covariance (EC) technique is the most direct method for measuring the exchange between the surface and the atm. in different ecosystems. Thus, it is commonly used to get information on air pollutant and greenhouse gas emissions, and on turbulent heat transfer. Typically an ecosystem is monitored by only one single EC measurement station at a time, making the ecosystem-level flux values subject to random and systematic uncertainties. Furthermore, in urban ecosystems we often have no choice but to conduct the single-point measurements in non-ideal locations such as close to buildings and/or in the roughness sublayer, bringing further complications to data anal. and flux estns. In order to tackle the question of how representative a single EC measurement point in an urban area can be, two identical EC systems - measuring momentum, sensible and latent heat, and carbon dioxide fluxes - were installed on each side of the same building structure in central Helsinki, Finland, during July 2013-Sept. 2015. The main interests were to understand the sensitivity of the vertical fluxes on the single measurement point and to est. the systematic uncertainty in annual cumulative values due to missing data if certain, relatively wide, flow-distorted wind sectors are disregarded. The momentum and measured scalar fluxes respond very differently to the distortion caused by the building structure. The momentum flux is the most sensitive to the measurement location, whereas scalar fluxes are less impacted. The flow distortion areas of the two EC systems (40-150 and 230-340°) are best detected from the mean-wind-normalized turbulent kinetic energy, and outside these areas the median relative random uncertainties of the studied fluxes measured by one system are between 12 % and 28 %. Different gapfilling methods with which to yield annual cumulative fluxes show how using data from a single EC measurement point can cause up to a 12 % (480 g C m-2) underestimation in the cumulative carbon fluxes as compared to combined data from the two systems. Combining the data from two EC systems also increases the fraction of usable half-hourly carbon fluxes from 45 % to 69 % at the annual level. For sensible and latent heat, the resp. underestimations are up to 5 % and 8 % (0.094 and 0.069 TJ m-2). The obtained random and systematic uncertainties are in the same range as obsd. in vegetated ecosystems. We also show how the commonly used data flagging criteria in natural ecosystems, kurtosis and skewness, are not necessarily suitable for filtering out data in a densely built urban environment. The results show how the single measurement system can be used to derive representative flux values for central Helsinki, but the addn. of second system to other side of the building structure decreases the systematic uncertainties. Comparable results can be expected in similarly dense city locations where no large directional deviations in the source area are seen. In general, the obtained results will aid the scientific community by providing information about the sensitivity of EC measurements and their quality flagging in urban areas.
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    Hollinger, D. Y.; Aber, J.; Dail, B.; Davidson, E. A.; Goltz, S. M.; Hughes, H.; Leclerc, M. Y.; Lee, J. T.; Richardson, A. D.; Rodrigues, C.; Scott, N. A.; Achuatavarier, D.; Walsh, J. Spatial and Temporal Variability in Forest-Atmosphere CO2 Exchange. Glob. Chang. Biol. 2004, 10 (10), 1689– 1706,  DOI: 10.1111/j.1365-2486.2004.00847.x
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    Sgrigna, G.; Baldacchini, C.; Esposito, R.; Calandrelli, R.; Tiwary, A.; Calfapietra, C. Characterization of Leaf-Level Particulate Matter for an Industrial City Using Electron Microscopy and X-Ray Microanalysis. Sci. Total Environ. 2016, 548–549, 91– 99,  DOI: 10.1016/j.scitotenv.2016.01.057
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    Characterization of leaf-level particulate matter for an industrial city using electron microscopy and X-ray microanalysis
    Sgrigna, G.; Baldacchini, C.; Esposito, R.; Calandrelli, R.; Tiwary, A.; Calfapietra, C.
    Science of the Total Environment (2016), 548-549 (), 91-99CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
    This study reports application of monitoring and characterization protocol for particulate matter (PM) deposited on tree leaves, using Quercus ilex as a case study species. The study area is located in the industrial city of Terni in central Italy, with high PM concns. Four trees were selected as representative of distinct pollution environments based on their proximity to a steel factory and a street. Wash off from leaves onto cellulose filters were characterized using SEM and energy dispersive X-ray spectroscopy, inferring the assocns. between particle sizes, chem. compn., and sampling location. Modeling of particle size distributions showed a tri-modal fingerprint, with the three modes centered at 0.6 (factory related), 1.2 (urban background), and 2.6 μm (traffic related). Chem. detection identified 23 elements abundant in the PM samples. Principal component anal. recognized iron and copper as source-specific PM markers, attributed mainly to industrial and heavy traffic pollution resp. Upscaling these results on leaf area basis provided a useful indicator for strategic evaluation of harmful PM pollutants using tree leaves.
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    Baldocchi, D. D. Assessing the Eddy Covariance Technique for Evaluating Carbon Dioxide Exchange Rates of Ecosystems: Past, Present and Future. Glob. Chang. Biol. 2003, 9 (4), 479– 492,  DOI: 10.1046/j.1365-2486.2003.00629.x
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    Hofman, J.; Wuyts, K.; Van Wittenberghe, S.; Samson, R. On the Temporal Variation of Leaf Magnetic Parameters: Seasonal Accumulation of Leaf-Deposited and Leaf-Encapsulated Particles of a Roadside Tree Crown. Sci. Total Environ. 2014, 493, 766– 772,  DOI: 10.1016/j.scitotenv.2014.06.074
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    On the temporal variation of leaf magnetic parameters: Seasonal accumulation of leaf-deposited and leaf-encapsulated particles of a roadside tree crown
    Hofman, Jelle; Wuyts, Karen; Van Wittenberghe, Shari; Samson, Roeland
    Science of the Total Environment (2014), 493 (), 766-772CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
    Understanding the accumulation behavior of atm. particles inside tree leaves is of great importance for the interpretation of biomagnetic monitoring results. This study evaluated the temporal variation of the satn. isothermal remanent magnetization (SIRM) of leaves of a roadside urban Platanus × acerifolia Willd. tree in Antwerp, Belgium. This study examd. the seasonal development of the total leaf SIRM signal as well as the leaf-encapsulated fraction of the deposited dust, by washing the leaves before biomagnetic anal. On av. 38% of the leaf SIRM signal was exhibited by the leaf-encapsulated particles. Significant correlations were found between the SIRM and the cumulative daily av. atm. PM10 and PM2.5 measurements. A steady increase of the SIRM throughout the in-leaf season was obsd. endorsing the applicability of biomagnetic monitoring as a proxy for the time-integrated PM exposure of urban tree leaves. Strongest correlations were obtained for the SIRM of the leaf-encapsulated particles which confirms the dynamic nature of the leaf surface-accumulated particles.
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    Ould-Dada, Z.; Baghini, N. M. Resuspension of Small Particles from Tree Surfaces. Atmos. Environ. 2001, 35 (22), 3799– 3809,  DOI: 10.1016/S1352-2310(01)00161-3
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    Resuspension of small particles from tree surfaces
    Ould-Dada, Zitouni; Baghini, Nasser M.
    Atmospheric Environment (2001), 35 (22), 3799-3809CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Science Ltd.)
    A detailed study of the resuspension of 1.85-μm MMAD (mass median aerodynamic diam.) silica particles from five horizontal layers within a small-scale spruce canopy was carried out in a wind tunnel in which saplings were exposed to a const. free stream wind speed of 5 m/s. This provided quant. ests. of the potential for a tree canopy contaminated with an aerosol deposit to provide (i) an airborne inhalation hazard within the forest environment and (ii) a secondary source of airborne contamination after an initial deposition event. Resuspension occurred with a flux of 1.05 × 10-7 g/m2-s from spruce saplings initially contaminated at a level of 4.1 × 10-2 g/m2. An av. resuspension rate (Λ) of 4.88 × 10-7/s was obtained for the canopy as a whole. Values of Λ were significantly different (ANOVA, p<0.001) between canopy layers, and Λ was markedly greater at the top of the canopy than lower down, although there was a slight increase in Λ at the base of the canopy. The resuspended silica particles deposited onto the soil surface at an av. rate of about 5.3 × 10-8 μg/cm2-s. It is concluded that resuspension under wind velocities similar to that used in the reported expts. is likely to pose a relatively small inhalation hazard to humans and a relatively minor source of secondary contamination of adjacent areas. Furthermore, resuspension rates are likely to diminish rapidly with time. The results are discussed in relation to the growing interest in tree planting schemes in urban areas to reduce the impacts of air pollution.
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    Järvi, L.; Rannik, Ü.; Mammarella, I.; Sogachev, A.; Aalto, P. P.; Keronen, P.; Siivola, E.; Kulmala, M.; Vesala, T. Annual Particle Flux Observations over a Heterogeneous Urban Area. Atmos. Chem. Phys. 2009, 9 (20), 7847– 7856,  DOI: 10.5194/acp-9-7847-2009
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    Annual particle flux observations over a heterogeneous urban area
    Jarvi, L.; Rannik, U.; Mammarella, I.; Sogachev, A.; Aalto, P. P.; Keronen, P.; Siivola, E.; Kulmala, M.; Vesala, T.
    Atmospheric Chemistry and Physics (2009), 9 (20), 7847-7856CODEN: ACPTCE; ISSN:1680-7316. (Copernicus Publications)
    Long-term eddy covariance particle no. flux measurements for the diam. range 6 nm to 5 μm were performed at the SMEAR III station over an urban area in Helsinki, Finland. The heterogeneity of the urban measurement location allowed us to study the effect of different land-use classes in different wind directions on the measured fluxes. The particle no. fluxes were highest in the direction of a local road on weekdays, with a daytime median flux of 0.8 × 109 m-2 s-1. The particle fluxes showed a clear dependence on traffic rates and on the mixing conditions of the boundary layer. The measurement footprint was estd. by the use of both numerical and anal. models. Using the crosswind integrated form of the footprint function, we estd. the emission factor for the mixed vehicle fleet, yielding a median particle no. emission factor per vehicle of 3.0 × 1014 # km-1. Particle fluxes from the vegetated area were the lowest with daytime median fluxes below 0.2 × 109 m-2 s-1. During weekends and nights, the particle fluxes were low from all land use sectors being in the order of 0.02-0.1 × 109 m-2 s-1. On an annual scale the highest fluxes were measured in winter, when emissions from stationary combustion sources are also highest. Particle no. fluxes were compared with the simultaneously measured CO2 fluxes and similarity in their sources was distinguishable. For CO2, the median emission factor of vehicles was estd. to be 370 g km-1.
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    Ueyama, M.; Ando, T. Diurnal, Weekly, Seasonal, and Spatial Variabilities in Carbon Dioxide Flux in Different Urban Landscapes in Sakai, Japan. Atmos. Chem. Phys. 2016, 16 (22), 14727– 14740,  DOI: 10.5194/acp-16-14727-2016
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    Diurnal, weekly, seasonal, and spatial variabilities in carbon dioxide flux in different urban landscapes in Sakai, Japan
    Ueyama, Masahito; Ando, Tomoya
    Atmospheric Chemistry and Physics (2016), 16 (22), 14727-14740CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
    To evaluate CO2 emissions in urban areas and their temporal and spatial variability, continuous measurements of CO2 fluxes were conducted using the eddy covariance method at three locations in Sakai, Osaka, Japan. Based on the flux footprint at the measurement sites, CO2 fluxes from the three sites were partitioned into five datasets representing a dense urban center, a moderately urban area, a suburb, an urban park, and a rural area. A distinct biol. uptake of CO2 was obsd. in the suburb, urban park, and rural areas in the daytime, whereas high emissions were obsd. in the dense and moderate urban areas in the daytime. Weekday CO2 emissions in the dense urban center and suburban area were approx. 50 % greater than emissions during weekends and holidays, but the other landscapes did not exhibit a clear weekly cycle. Seasonal variations in the urban park, rural area, and suburban area were influenced by photosynthetic uptake, exhibiting the lowest daily emissions or even uptake during the summer months. In contrast, the dense and moderately urban areas emitted CO2 in all seasons. CO2 emissions in the urban areas were high in the winter and summer months, and they significantly increased with the increase in air temp. in the summer and the decrease in air temp. in the winter. Irresp. of the land cover type, all urban landscapes measured in this study acted as net annual CO2 sources, with emissions ranging from 0.5 to 4.9 kg C m-2 yr-1. The magnitude of the annual CO2 emissions was neg. correlated with the green fraction; areas with a smaller green fraction had higher annual CO2 emissions. Upscaled flux estd. based on the green fraction indicated that the emissions for the entire city were 3.3 kg C m-2 yr-1, which is equiv. to 0.5 Tg C yr-1 or 1.8 Mt CO2 yr-1, based on the area of the city (149.81 km2). A network of eddy covariance measurements is useful for characterizing the spatial and temporal variations in net CO2 fluxes from urban areas. Multiple methods would be required to evaluate the rationale behind the fluxes and overcome the limitations in the future.
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  • Abstract

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    Figure 1

    Figure 1. Wind speed, precipitation, and PM2.5 concentration throughout the two measurement campaigns. Particulate matter data are reported for the period DOY 1–32 up to the leaf sampling day (February 1st).

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    Figure 2

    Figure 2. Modeled cumulative PM2.5 (At) calculated according to the i-Tree Eco standard parametrization (i-Tree) and broadleaf specific deposition velocity (Broadleaf), compared with leaf measurements of the PM2.5 load by SEM/EDX and vacuum filtration (VF), on leaves collected on February 1, 2017 (min = 2.4; max = 7.9 μg cm–2). Precipitation events above the maximum water storage of the canopy (Ps) wash off leaves and set the cumulative flux to 0.

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    Figure 3

    Figure 3. Top left: Hourly average net flux throughout the day (DOY 1–32) modeled using the i-Tree Eco standard parametrization (i-Tree) and the specific parametrization for broadleaved species (Broadleaf). Bottom left: Hourly average wind speed (ws) and particulate matter concentration (PM2.5) throughout the day during the same period. Top right: Half-hourly average net flux (DOY 164–249) measured by the eddy covariance (EC) and simulated fluxes using either the i-Tree Eco standard parametrization (i-Tree) or the specific parametrization for broadleaved species (Broadleaf). Bottom right: Half-hourly average wind speed (ws) and particulate matter concentration (PM2.5) throughout the day during the same period.

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    Figure 4

    Figure 4. Sensitivity analysis of the modeled PM2.5 accumulation on leaves (DOY 1–32) to the deposition velocity (vds), potential leaf water storage (plws), resuspension classes (rr), leaf washing (washing), and combining the different parametrization (combo). The dashed line indicates the leaf PM2.5 load range measured with SEM/EDX and VF collected on February 1, 2017 (min = 2.4; max = 7.9 μg cm–2).

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    Figure 5

    Figure 5. Sensitivity analysis of the modeled PM2.5 net flux to the deposition velocity (vds), potential leaf water storage (plws), resuspension classes (rr), leaf washing (washing), and combining the different parametrization (combo) compared with the eddy covariance flux (DOY 164–249).

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  • References

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      Livesley, S. J.; McPherson, E. G.; Calfapietra, C. The Urban Forest and Ecosystem Services: Impacts on Urban Water, Heat, and Pollution Cycles at the Tree, Street, and City Scale. J. Environ. Qual. 2016, 45 (1), 119– 124,  DOI: 10.2134/jeq2015.11.0567
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      The urban forest and ecosystem services: impacts on urban water, heat, and pollution cycles at the tree, street, and city scale
      Livesley, S. J.; McPherson, G. M.; Calfapietra, C.
      Journal of Environmental Quality (2016), 45 (1), 119-124CODEN: JEVQAA; ISSN:1537-2537. (American Society of Agronomy)
      Many environmental challenges are exacerbated within the urban landscape, such as stormwater runoff and flood risk, chem. and particulate pollution of urban air, soil and water, the urban heat island, and summer heat waves. Urban trees, and the urban forest as a whole, can be managed to have an impact on the urban water, heat, carbon and pollution cycles. However, there is an increasing need for empirical evidence as to the magnitude of the impacts, both beneficial and adverse, that urban trees can provide and the role that climatic region and built landscape circumstance play in modifying those impacts. This special section presents new research that advances our knowledge of the ecol. and environmental services provided by the urban forest. The 14 studies included provide a global perspective on the role of trees in towns and cities from five continents. Some studies provide evidence for the cooling benefit of the local microclimate in urban green space with and without trees. Other studies focus solely on the cooling benefit of urban tree transpiration at a mesoscale or on cooling from canopy shade at a street and pedestrian scale. Other studies are concerned with tree species differences in canopy interception of rainfall, water uptake from biofilter systems, and water quality improvements through nutrient uptake from stormwater runoff. Research reported here also considers both the pos. and the neg. impacts of trees on air quality, through the role of trees in removing air pollutants such as ozone as well as in releasing potentially harmful volatile org. compds. and allergenic particulates. A transdisciplinary framework to support future urban forest research is proposed to better understand and communicate the role of urban trees in urban biogeochem. cycles that are highly disturbed, highly managed, and of paramount importance to human health and well-being.
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    6. 6
      Calfapietra, C.; Cherubini, L. Green Infrastructure: Nature-Based Solutions for Sustainable and Resilient Cities. Urban For. Urban Green. 2019, 37 (2018), 1– 2,  DOI: 10.1016/j.ufug.2018.09.012
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      Nowak, D. J.; Hirabayashi, S.; Bodine, A.; Hoehn, R. Modeled PM2.5 Removal by Trees in Ten U.S. Cities and Associated Health Effects. Environ. Pollut. 2013, 178, 395– 402,  DOI: 10.1016/j.envpol.2013.03.050
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      Modeled PM2.5 removal by trees in ten U.S. cities and associated health effects
      Nowak, David J.; Hirabayashi, Satoshi; Bodine, Allison; Hoehn, Robert
      Environmental Pollution (Oxford, United Kingdom) (2013), 178 (), 395-402CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
      Urban particulate air pollution is a serious health issue. Trees within cities can remove fine particles from the atm. and consequently improve air quality and human health. Tree effects on PM2.5 concns. and human health are modeled for 10 U.S. cities. The total amt. of PM2.5 removed annually by trees varied from 4.7 tonnes in Syracuse to 64.5 tonnes in Atlanta, with annual values varying from $1.1 million in Syracuse to $60.1 million in New York City. Most of these values were from the effects of reducing human mortality. Mortality redns. were typically around 1 person yr-1 per city, but were as high as 7.6 people yr-1 in New York City. Av. annual percent air quality improvement ranged between 0.05% in San Francisco and 0.24% in Atlanta. Understanding the impact of urban trees on air quality can lead to improved urban forest management strategies to sustain human health in cities.
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    8. 8
      Beckett, K. P.; Freer-Smith, P. H.; Taylor, G. Particulate Pollution Capture by Urban Trees: Effect of Species and Windspeed. Glob. Chang. Biol. 2000, 6 (8), 995– 1003,  DOI: 10.1046/j.1365-2486.2000.00376.x
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      Freer-Smith, P. H.; El-Khatib, A. A.; Taylor, G. Capture of Particulate Pollution by Trees: A Comparison of Species Typical of Semi-Arid Areas (Ficus Nitida and Eucalyptus Globulus) with European and North American Species. Water, Air, Soil Pollut. 2004, 155 (1), 173– 187,  DOI: 10.1023/B:WATE.0000026521.99552.fd
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      Capture of Particulate Pollution by Trees: A Comparison of Species Typical of Semi-Arid Areas (Ficus Nitida and Eucalyptus Globulus) with European and North American Species
      Freer-Smith, P. H.; El-Khatib, A. A.; Taylor, Gail
      Water, Air, and Soil Pollution (2004), 155 (1-4), 173-187CODEN: WAPLAC; ISSN:0049-6979. (Kluwer Academic Publishers)
      Particulate pollution is a serious concern in developed countries esp. in urban and suburban areas where it has adverse effects on human health, exacerbating a wide range of respiratory and vascular illnesses. Data are now available which indicate that similar problems probably occur in countries in transition and may indeed be worse where national air quality stds. have been neither set nor monitored. Recently a variety of approaches using both wind tunnel and field measurements have suggested that trees can significantly reduce such adverse effects through their ability to capture pollutant particles. It is clear that species choice, planting design and location relative to pollution source are crit. in detg. the effectiveness of particle capture by trees. Here we present relative deposition velocities and capture efficiencies of five species used widely in woodland of urban and periurban areas of Europe (Quercus petraea (oak), Alnus glutinosa (alder), Fraxinus excelsior (ash), Acer pseudo-platanus (sycamore) and Pseudotsuga menziesii (Douglas fir)), and for two species being used increasingly in semi-arid regions, (Ficus nitida (weeping fig) and Eucalyptus. globulus (Eucalyptus)). These data are for species not previously worked on and measurements were made at three windspeeds. Deposition velocities and capture efficiencies are compared with those published for other tree species, with the values of deposition velocity ranging from 0.1 to 0.3 cm s -1 at a windspeed of 3 m s -1 to max. values 2.9 cm s -1 at 9 m s -1 windspeed. Species with more complex stem structure and smaller leaves had greater relative deposition velocities. The use of such data in models to guide species choice and planting design in order to maximise particle removal from urban air are considered.
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    10. 10
      Xu, X.; Zhang, Z.; Bao, L.; Mo, L.; Yu, X.; Fan, D.; Lun, X. Influence of Rainfall Duration and Intensity on Particulate Matter Removal from Plant Leaves. Sci. Total Environ. 2017, 609, 11– 16,  DOI: 10.1016/j.scitotenv.2017.07.141
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      10
      Influence of rainfall duration and intensity on particulate matter removal from plant leaves
      Xu, Xiaowu; Zhang, Zhenming; Bao, Le; Mo, Li; Yu, Xinxiao; Fan, Dengxing; Lun, Xiaoxiu
      Science of the Total Environment (2017), 609 (), 11-16CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
      Rainfall influences removal of airborne particulate matter (PM) from leaf surfaces through a process called wash off resulting in throughfall that carries PM to the ground. The present study examd. the effects of rainfall characteristics on PM wash-off mass and rate from the foliage of four broadleaf species, to investigate retention of PM pollution. In a controlled rainfall simulation expt., rainfall intensity was set to 15, 30, and 50 mm h- 1, and sampling intervals for the three rainfall intensities were divided into 10, 5, and 3 min, resp. Of the plants examd., the evergreen shrub Euonymus japonicus had the greatest surface PM accumulation before rainfall (165 μg cm- 2), max. wash-off during the first 2.5 mm of rain (30 μg cm- 2), and max. surface PM retention after rainfall (24 μg cm- 2). Fitting observations with the Box Lucas regression model, cumulative PM wash-off rates increased with cumulative rainfall amt., until the curves tended to become steady after rain exceeded 12.5 mm. Wash off removed 51 to 70% of surface PM accumulation. As rainfall intensity increased, the duration of PM wash-off decreased, and wash-off rates were highest during the first rainfall interval. However, there was no significant difference between PM wash-off rates for rainfall intensities of 30 and 50 mm h- 1 in each rainfall interval. In addn., rain did not remove all PM completely, and PM retention following rainfall differed with rainfall intensity, except for Populus tomentosa.
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    11. 11
      Jeanjean, A. P. R.; Monks, P. S.; Leigh, R. J. Modelling the Effectiveness of Urban Trees and Grass on PM2.5 Reduction via Dispersion and Deposition at a City Scale. Atmos. Environ. 2016, 147, 1– 10,  DOI: 10.1016/j.atmosenv.2016.09.033
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      11
      Modelling the effectiveness of urban trees and grass on PM2.5 reduction via dispersion and deposition at a city scale
      Jeanjean, A. P. R.; Monks, P. S.; Leigh, R. J.
      Atmospheric Environment (2016), 147 (), 1-10CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
      Green infrastructure can reduce PM2.5 traffic emissions on a city scale, by a combination of dispersion by trees and deposition on buildings, trees and grass. Simulations of PM2.5 concns. were performed using a validated CFD model. A 2 × 2 km area has been reconstructed as a 3D representation of Leicester (UK) city center which is on a scale larger than most of the other CFD studies. Combining both the effects of tree aerodynamics and the deposition capabilities of trees and grass is also something that has not yet been modelled at this scale. During summer time in Leicester City, the results show that the aerodynamic dispersive effect of trees on PM2.5 concns. result in a 9.0% redn. In contrast, a decrease of PM2.5, by 2.8% owing to deposition on trees (11.8 t year-1) and 0.6% owing to deposition on grass (2.5 t year-1), was also obsd. Trees and grass are shown to have greater effects locally, as smaller decreases in PM2.5 were found when considering redn. across the whole boundary layer. Densely built areas like Leicester City center have relatively less vegetation and subsequently have a smaller effect on PM2.5 concn. It was found that particle deposition on buildings was negligible with less than 0.03%. An empirical equation was derived to describe the changes in PM2.5 based on ground surface fraction of trees and grass, and their deposition velocities.
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      Buccolieri, R.; Santiago, J. L.; Rivas, E.; Sanchez, B. Review on Urban Tree Modelling in CFD Simulations: Aerodynamic, Deposition and Thermal Effects. Urban For. Urban Green. 2018, 31, 212– 220,  DOI: 10.1016/j.ufug.2018.03.003
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      Lin, J.; Kroll, C. N.; Nowak, D. J.; Greenfield, E. J. A Review of Urban Forest Modeling: Implications for Management and Future Research. Urban For. Urban Green. 2019, 43, 126366,  DOI: 10.1016/j.ufug.2019.126366
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      Sgrigna, G.; Baldacchini, C.; Dreveck, S.; Cheng, Z.; Calfapietra, C. Relationships between Air Particulate Matter Capture Efficiency and Leaf Traits in Twelve Tree Species from an Italian Urban-Industrial Environment. Sci. Total Environ. 2020, 718, 137310,  DOI: 10.1016/j.scitotenv.2020.137310
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      Relationships between air particulate matter capture efficiency and leaf traits in twelve tree species from an Italian urban-industrial environment
      Sgrigna, G.; Baldacchini, C.; Dreveck, S.; Cheng, Z.; Calfapietra, C.
      Science of the Total Environment (2020), 718 (), 137310CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
      Air pollution in the urban environment is widely recognized as one of the most harmful threats for human health. International organizations such as the United Nations and the European Commission are highlighting the potential role of nature in mitigating air pollution and are now funding the implementation of Nature-Based Solns., esp. at the city level. Over the past few decades, the attention of the scientific community has grown around the role of urban forest in air pollution mitigation. Nevertheless, the understanding on Particulate Matter (PM) retention mechanisms by tree leaves is still limited. In this study, twelve tree species were sampled within an urban park of an industrial city. Two techniques were used for leaf anal.: Vacuum/Filtration and SEM coupled with Energy Dispersive x-ray spectroscopy, to obtain a quali-quant. anal. of the different PM size fractions. Results showed that deposited PM loads vary significantly among species. Different leaf traits, including micro and macromorphol. characteristics, were obsd., measured and ranked, with the final aim to relate them with PM load. Even if no significant correlation between each single leaf characteristic and PM deposition was obsd. (p > 0.05), multivariate anal. revealed relationships between clusters of leaf traits and deposited PM. Thus, by assigning a score to each trait, an Accumulation index (Ai) was calcd., which was significantly related to the leaf deposited PM load (p ≤ 0.05).
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    15. 15
      Wang, L.; Gong, H.; Liao, W.; Wang, Z. Accumulation of Particles on the Surface of Leaves during Leaf Expansion. Sci. Total Environ. 2015, 532, 420– 434,  DOI: 10.1016/j.scitotenv.2015.06.014
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      15
      Accumulation of particles on the surface of leaves during leaf expansion
      Wang, Lei; Gong, Huili; Liao, Wenbo; Wang, Zhi
      Science of the Total Environment (2015), 532 (), 420-434CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
      Plants effectively remove particles from ambient air to consequently improve air quality and human health. Particle accumulation on leaf surfaces of 3 plant species with different epicuticular wax ultrastructures (thin films, platelets, tubules), was assessed during leaf expansion in Beijing, China, under extremely high particulate matter (PM) concns. Particle accumulation on leaf surfaces following bud break rapidly reached a high amt. within 4-7 days. Rainfall occasionally resulted in a considerable increase in leaf surface particle accumulation at high PM concns., resulting from wet PM deposition, balancing the amt. of PM on leaf surfaces over a longer period. The equil. value of the adaxial leaf surface particle cover area of the 3 test species was 10-50% vs. 3-35% on the abaxial leaf surface. Epicuticular wax ultrastructures significantly contributed to leaf PM adsorption. The capacity of these ultrastructures to capture PM decreased in the following order: thin films > platelets > tubules. Leaf surface ridges (1-2 μm scale) more efficiently accumulated PM, particularly PM2.5, vs. roughness (P-V distance) on a 5-20 μm scale.
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    16. 16
      Muhammad, S.; Wuyts, K.; Samson, R. Atmospheric Net Particle Accumulation on 96 Plant Species with Contrasting Morphological and Anatomical Leaf Characteristics in a Common Garden Experiment. Atmos. Environ. 2019, 202, 328– 344,  DOI: 10.1016/j.atmosenv.2019.01.015
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      16
      Atmospheric net particle accumulation on 96 plant species with contrasting morphological and anatomical leaf characteristics in a common garden experiment
      Muhammad, S.; Wuyts, K.; Samson, R.
      Atmospheric Environment (2019), 202 (), 328-344CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
      In this study, we investigated leaves of 96 perennial urban plant species consisting of 43 deciduous broadleaf trees, 32 deciduous broadleaf shrubs, 14 deciduous and evergreen needle/scale-like, 5 evergreen broadleaves, and 2 climber species for their differences in net particle accumulation. Leaf satn. isothermal remanent magnetization (SIRM), a proxy for traffic and industry induced particle accumulation, along with morphol. and anatomical leaf traits were analyzed in a common garden expt. in June and Sept. 2016. Leaf SIRM varied significantly between plant species. The most effective net particle accumulating plant species with a median value of 23.0μA were Buddleja davidii, Viburnum opulus, Carpinus betulus, Quercus ilex, Viburnum lantana, Rosa rugosa, Sorbus aria, Aesculus hippocastanum, Pseudotsuga menziesii, Acer campestre. The least effective net particle accumulating plant species with a median value of 10.4μA were Populus alba, Alnus glutinosa, Larix kaempferi, Larix decidua, Plantanus x acerilifolia, Acer pseudoplatanus, Robinia pseudoacacia, Quercus palustris, Rosa canina, Liquidambar styraciflua. The "variable importance" in net particle accumulation for the investigated plant species was achieved using randomForest. The presence of leaf trichomes and specific leaf area were identified as important leaf traits for categorization of the selected plant species in low, medium, and high net particle accumulators.
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    17. 17
      Shao, F.; Wang, L.; Sun, F.; Li, G.; Yu, L.; Wang, Y.; Zeng, X.; Yan, H.; Dong, L.; Bao, Z. Study on Different Particulate Matter Retention Capacities of the Leaf Surfaces of Eight Common Garden Plants in Hangzhou, China. Sci. Total Environ. 2019, 652, 939– 951,  DOI: 10.1016/j.scitotenv.2018.10.182
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      17
      Study on different particulate matter retention capacities of the leaf surfaces of eight common garden plants in Hangzhou, China
      Shao Feng; Wang Lihua; Li Guo; Yu Lu; Wang Yujie; Zeng Xinru; Yan Hai; Sun Fengbin; Dong Li; Bao Zhiyi
      The Science of the total environment (2019), 652 (), 939-951 ISSN:.
      The severity of inhalable particulate matter (PM) pollution in the atmosphere is increasing; however, plants can effectively reduce the concentration of atmospheric PM by retaining it on their leaves. In this paper, eight common garden plants in Hangzhou, China, were selected as the study objects to observe the morphological features of the leaf surfaces and the retained particles and to analyze the elemental composition of the particles. Confocal laser scanning microscopy (CLSM) was performed to detect the morphological features of the leaf surfaces, and the relationship between the roughness of the leaf surface and the number of the retained particulates was quantitatively analyzed. In addition, the elements in the soil were measured via inductively coupled plasma-optical emission spectrometry (ICP-OES) to locate the possible particulate sources. The results revealed that leaves are able to retain particulates via the synergy of multiple microstructures on the leaf surface, such as grooves, folds, small chambers, flocculus projections, long villi, pubescent hairs and waxes. Moreover, the leaf surface roughness is closely related to the number of retained particulates, with rougher surfaces corresponding to more rugged folds and grooves and a stronger retention ability. The retained particulates are primarily composed of C, O, Si, Al, Ca, K, Mg, Nb, Fe, Na and Ti, and a comparison with the elements in the soil samples indicated that these elements originated from soil dust. Among the different particle sizes, PM with a diameter <2.5 μm (PM2.5) presented the greatest retention on the surfaces of the different plant leaves, while a much smaller amount of PM with a diameter larger than 10 μm was retained. The research results provide an important theoretical scientific basis for the mechanism underlying PM adsorption by plants and strategies for the reasonable selection of garden dust-retaining tree species.
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      Chen, L.; Liu, C.; Zhang, L.; Zou, R.; Zhang, Z. Variation in Tree Species Ability to Capture and Retain Airborne Fine Particulate Matter (PM2.5). Sci. Rep. 2017, 7 (1), 1– 11,  DOI: 10.1038/s41598-017-03360-1
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      18
      Erratum: Reduced GABAergic transmission in the ventrobasal thalamus contributes to thermal hyperalgesia in chronic inflammatory pain
      Zhang, Chan; Chen, Rong-Xiang; Zhang, Yu; Wang, Jie; Liu, Feng-Yu; Cai, Jie; Liao, Fei-Fei; Xu, Fu-Qiang; Yi, Ming; Wan, You
      Scientific Reports (2017), 7 (1), 1-6CODEN: SRCEC3; ISSN:2045-2322. (Nature Research)
      Scientific Reports 7: Article no.: 41439; published online: 02 Feb. 2017; updated: 04 May 2017 This Article contains errors in Figures 1, 2, 3, 4, 5, 6, 7 and 8. In Figure 1, n = 7 was omitted from panel C. In Figure 2, labels are missing from the bars of panel B. In Figure 3, 'Control' was incorrectly given as 'Sham', labels are missing from the bars in Figure 3B and C, and n = 7 and n = 9 were omitted from Figure 3E.
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    19. 19
      Räsänen, J. V.; Holopainen, T.; Joutsensaari, J.; Ndam, C.; Pasanen, P.; Rinnan, Å.; Kivimäenpää, M. Effects of Species-Specific Leaf Characteristics and Reduced Water Availability on Fine Particle Capture Efficiency of Trees. Environ. Pollut. 2013, 183, 64– 70,  DOI: 10.1016/j.envpol.2013.05.015
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      19
      Effects of species-specific leaf characteristics and reduced water availability on fine particle capture efficiency of trees
      Rasanen, Janne V.; Holopainen, Toini; Joutsensaari, Jorma; Ndam, Collins; Pasanen, Pertti; Rinnan, Asmund; Kivimaenpaa, Minna
      Environmental Pollution (Oxford, United Kingdom) (2013), 183 (), 64-70CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
      Trees can improve air quality by capturing particles in their foliage. We detd. the particle capture efficiencies of coniferous Pinus sylvestris and three broadleaved species: Betula pendula, Betula pubescens and Tilia vulgaris in a wind tunnel using NaCl particles. The importance of leaf surface structure, physiol. and moderate soil drought on the particle capture efficiencies of the trees were detd. The results confirm earlier findings of more efficient particle capture by conifers compared to broadleaved plants. The particle capture efficiency of P. sylvestris (0.21%) was significantly higher than those of B. pubescens, T. vulgaris and B. pendula (0.083%, 0.047%, 0.043%, resp.). The small leaf size of P. sylvestris was the major characteristic that increased particle capture. Among the broadleaved species, low leaf wettability, low stomatal d. and leaf hairiness increased particle capture. Moderate soil drought tended to increase particle capture efficiency of P. sylvestris.
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    20. 20
      Weerakkody, U.; Dover, J. W.; Mitchell, P.; Reiling, K. Quantification of the Traffic-Generated Particulate Matter Capture by Plant Species in a Living Wall and Evaluation of the Important Leaf Characteristics. Sci. Total Environ. 2018, 635, 1012– 1024,  DOI: 10.1016/j.scitotenv.2018.04.106
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      20
      Quantification of the traffic-generated particulate matter capture by plant species in a living wall and evaluation of the important leaf characteristics
      Weerakkody, Udeshika; Dover, John W.; Mitchell, Paul; Reiling, Kevin
      Science of the Total Environment (2018), 635 (), 1012-1024CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
      Traffic-generated particulate matter (PM) is a significant fraction of urban PM pollution and little is known about the use of living walls as a short-term strategy to reduce this pollution. The present study evaluated the potential of twenty living wall plants to reduce traffic-based PM using a living wall system located along a busy road in Stoke-on-Trent, UK. An Environmental Scanning Electron Microscope (ESEM) and ImageJ software were employed to quantify PM accumulation on leaves (PM1, PM2.5 and PM10) and their elemental compn. was detd. using Energy Dispersive X-ray (EDX). Inter-species variation in leaf-PM accumulation was evaluated using a Generalized Linear Mixed-effect Model (GLMM) using time as a factor; any differential PM accumulation due to specific leaf characteristics (stomatal d., hair/trichomes, ridges and grooves) was identified. The study showed a promising potential for living wall plants to remove atm. PM; an estd. av. no. of 122.08 ± 6.9 × 107 PM1, 8.24 ± 0.72 × 107 PM2.5 and 4.45 ± 0.33 × 107 PM10 were captured on 100 cm2 of the living wall used in this study. Different species captured significantly different quantities of all particle sizes; the highest amt. of all particle sizes was found on the leaf-needles of Juniperus chinensis L., followed by smaller-leaved species. In the absence of an apparent pattern in correlation between PM accumulation and leaf surface characteristics, the study highlighted the importance of individual leaf size in PM capture irresp. of their variable micro-morphol. The elemental compn. of the captured particles showed a strong correlation with traffic-based PM and a wide range of important heavy metals. We conclude that the use of living walls that consist largely of smaller-leaved species and conifers can potentially have a significant impact in ameliorating air quality by removing traffic-generated PM pollution to improve the wellbeing of urban dwellers.
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    21. 21
      Pace, R.; Grote, R. Deposition and Resuspension Mechanisms Into and From Tree Canopies: A Study Modeling Particle Removal of Conifers and Broadleaves in Different Cities. Front. For. Glob. Chang. 2020, 3 (March), 26,  DOI: 10.3389/ffgc.2020.00026
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    22. 22
      Hofman, J.; Samson, R. Biomagnetic Monitoring as a Validation Tool for Local Air Quality Models: A Case Study for an Urban Street Canyon. Environ. Int. 2014, 70 (2014), 50– 61,  DOI: 10.1016/j.envint.2014.05.007
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      22
      Biomagnetic monitoring as a validation tool for local air quality models: a case study for an urban street canyon
      Hofman Jelle; Samson Roeland
      Environment international (2014), 70 (), 50-61 ISSN:.
      Biomagnetic monitoring of tree leaf deposited particles has proven to be a good indicator of the ambient particulate concentration. The objective of this study is to apply this method to validate a local-scale air quality model (ENVI-met), using 96 tree crown sampling locations in a typical urban street canyon. To the best of our knowledge, the application of biomagnetic monitoring for the validation of pollutant dispersion modeling is hereby presented for the first time. Quantitative ENVI-met validation showed significant correlations between modeled and measured results throughout the entire in-leaf period. ENVI-met performed much better at the first half of the street canyon close to the ring road (r=0.58-0.79, RMSE=44-49%), compared to second part (r=0.58-0.64, RMSE=74-102%). The spatial model behavior was evaluated by testing effects of height, azimuthal position, tree position and distance from the main pollution source on the obtained model results and magnetic measurements. Our results demonstrate that biomagnetic monitoring seems to be a valuable method to evaluate the performance of air quality models. Due to the high spatial and temporal resolution of this technique, biomagnetic monitoring can be applied anywhere in the city (where urban green is present) to evaluate model performance at different spatial scales.
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    23. 23
      Fares, S.; Savi, F.; Fusaro, L.; Conte, A.; Salvatori, E.; Aromolo, R.; Manes, F. Particle Deposition in a Peri-Urban Mediterranean Forest. Environ. Pollut. 2016, 218, 1278– 1286,  DOI: 10.1016/j.envpol.2016.08.086
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      23
      Particle deposition in a peri-urban Mediterranean forest
      Fares, Silvano; Savi, Flavia; Fusaro, Lina; Conte, Adriano; Salvatori, Elisabetta; Aromolo, Rita; Manes, Fausto
      Environmental Pollution (Oxford, United Kingdom) (2016), 218 (), 1278-1286CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
      Urban and peri-urban forests provide a multitude of Ecosystem Services to the citizens. While the capacity of removing carbon dioxide and gaseous compds. from the atm. has been tested, their capacity to sequestrate particles (PM) has been poorly investigated. Mediterranean forest ecosystems are often located nearby or inside large urban areas. This is the case of the city of Rome, Italy, which hosts several urban parks and is surrounded by forested areas. In particular, the Presidential Estate of Castelporziano is a 6000 ha forested area located between the Tyrrhenian coast and the city (25 km downtown of Rome). Under the hypothesis that forests can ameliorate air quality thanks to particle deposition, we measured fluxes of PM1, 2.5 and 10 with fast optical sensors and eddy covariance technique. We found that PM1 is mainly deposited during the central hours of the day, while negligible fluxes were obsd. for PM 2.5 and 10. A Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT v4) simulated PM emission from traffic areas in the city of Rome and showed that a significant portion of PM is removed by vegetation in the days when the plume trajectory meets the urban forest.
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    24. 24
      Fares, S.; Alivernini, A.; Conte, A.; Maggi, F. Ozone and Particle Fluxes in a Mediterranean Forest Predicted by the AIRTREE Model. Sci. Total Environ. 2019, 682, 494– 504,  DOI: 10.1016/j.scitotenv.2019.05.109
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      24
      Ozone and particle fluxes in a Mediterranean forest predicted by the AIRTREE model
      Fares, Silvano; Alivernini, Alessandro; Conte, Adriano; Maggi, Federico
      Science of the Total Environment (2019), 682 (), 494-504CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
      Mediterranean forests are among the most threatened ecosystems from the concurrent effects of climate change and air pollution. This work parameterized the AIRTREE multi-layer model to predict CO2, water, O3, and fine particle exchanges between leaves and the atm. AIRTREE consists of four different modules: canopy environmental module which dets. leaf temp. and radiative fluxes at different levels from above to the bottom of the canopy; a hydrol. module which predicts soil water flow and water availability to plant photosynthetic app.; a photosynthesis module which ests. the net photosynthesis and stomatal conductance; and a deposition module which ests. O3 and PM deposition sinks as a function of gas diffusion resistance in the atm. and within the canopy and leaf boundary layer. AIRTREE model framework, accuracy, and sensitivity are described by comparing modeling results against long-term continuous eddy covariance O3, water, and CO2 flux measurements in a Mediterranean Holm oak forest. Potential use of AIRTREE for O3 risk assessment in relation to the availability of a large observational database from ecosystems distributed worldwide is also discussed.
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    25. 25
      Dzierzanowski, K.; Popek, R.; Gawrońska, H.; Saebø, A.; Gawroński, S. W. Deposition of Particulate Matter of Different Size Fractions on Leaf Surfaces and in Waxes of Urban Forest Species. Int. J. Phytorem. 2011, 13 (10), 1037– 1046,  DOI: 10.1080/15226514.2011.552929
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      25
      Deposition of Particulate Matter of Different Size Fractions on Leaf Surfaces and in Waxes of Urban Forest Species
      Dzierzanowski, Kajetan; Popek, Robert; Gawronska, Helena; Saebo, Arne; Gawronski, Stanislaw W.
      International Journal of Phytoremediation (2011), 13 (10), 1037-1046CODEN: IJPHFG; ISSN:1522-6514. (Taylor & Francis, Inc.)
      Particulate matter (PM) is an air contaminant in urban and industrial areas that often exceeds limit values, creating serious problems due to its harmful effects on health. Planting trees and shrubs as air filters is a way to improve air quality in these areas. However, further knowledge on species effectiveness in air purifn. is essential. This study compared four species of tree (Acer campestre L., Fraxinus excelsior L., Platanus × hispanica Mill. ex Muenchh. 'Acerifolia', Tilia cordata Mill.), three species of shrub (Forsythia × intermedia Zabel, Physocarpus opulifolius (L.) Maxim., Spiraea japonica L.), and one climber species (Hedera helix L.) that are commonly cultivated along streets in Poland to capture fine, coarse and larger particles from air. Sep. gravimetric analyses were performed to quantify PM deposited on surfaces and trapped in waxes. Significant differences were found between the plant species tested. The distribution of different particle size fractions differed between and within species and also between leaf surfaces and in waxes.
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    26. 26
      Sæbø, A.; Popek, R.; Nawrot, B.; Hanslin, H. M.; Gawronska, H.; Gawronski, S. W. Plant Species Differences in Particulate Matter Accumulation on Leaf Surfaces. Sci. Total Environ. 2012, 427–428, 347– 354,  DOI: 10.1016/j.scitotenv.2012.03.084
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      26
      Plant species differences in particulate matter accumulation on leaf surfaces
      Saebo A; Popek R; Nawrot B; Hanslin H M; Gawronska H; Gawronski S W
      The Science of the total environment (2012), 427-428 (), 347-54 ISSN:.
      Particulate matter (PM) accumulation on leaves of 22 trees and 25 shrubs was examined in test fields in Norway and Poland. Leaf PM in different particle size fractions (PM(10), PM(2.5), PM(0.2)) differed among the species, by 10- to 15-folds at both test sites. Pinus mugo and Pinus sylvestris, Taxus media and Taxus baccata, Stephanandra incisa and Betula pendula were efficient species in capturing PM. Less efficient species were Acer platanoides, Prunus avium and Tilia cordata. Differences among species within the same genus were also observed. Important traits for PM accumulation were leaf properties such as hair and wax cover. The ranking presented in terms of capturing PM can be used to select species for air pollution removal in urban areas. Efficient plant species and planting designs that can shield vulnerable areas in urban settings from polluting traffic etc. can be used to decrease human exposure to anthropogenic pollutants.
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    27. 27
      Mo, L.; Ma, Z.; Xu, Y.; Sun, F.; Lun, X.; Liu, X.; Chen, J.; Yu, X. Assessing the Capacity of Plant Species to Accumulate Particulate Matter in Beijing, China. PLoS One 2015, 10 (10), e0140664– 18,  DOI: 10.1371/journal.pone.0140664
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      Assessing the capacity of plant species to accumulate particulate matter in Beijing, China
      Mo, Li; Ma, Zeyu; Xu, Yansen; Sun, Fengbin; Lun, Xiaoxiu; Liu, Xuhui; Chen, Jungang; Yu, Xinxiao
      PLoS One (2015), 10 (10), e0140664/1-e0140664/18CODEN: POLNCL; ISSN:1932-6203. (Public Library of Science)
      Air pollution causes serious problems in spring in northern China; therefore, studying the ability of different plants to accumulate particulate matter (PM) at the beginning of the growing season may benefit urban planners in their attempts to control air pollution. This study evaluated deposits of PM on the leaves and in the wax layer of 35 species (11 shrubs, 24 trees) in Beijing, China. Differences in the accumulation of PM were obsd. between species. Cephalotaxus sinensis, Euonymus japonicus, Broussonetia papyriferar, Koelreuteria paniculata and Quercus variabilis were all efficient in capturing small particles. The plants exhibiting high amts. of total PM accumulation (on leaf surfaces and/or in the wax layer), also showed comparatively high levels of PM accumulation across all particle sizes. A comparison of shrubs and trees did not reveal obvious differences in their ability to accumulate particles based on growth form; a combination of plantings with different growth forms can efficiently reduce airborne PM concns. near the ground. To test the relationships between leaf traits and PM accumulation, leaf samples of selected species were obsd. using a scanning electron microscope. Growth forms with greater amts. of pubescence and increased roughness supported PM accumulation; the adaxial leaf surfaces collected more particles than the abaxial surfaces. The results of this study may inform the selection of species for urban green areas where the goal is to capture air pollutants and mitigate the adverse effects of air pollution on human health.
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    28. 28
      Sgrigna, G.; Sæbø, A.; Gawronski, S.; Popek, R.; Calfapietra, C. Particulate Matter Deposition on Quercus Ilex Leaves in an Industrial City of Central Italy. Environ. Pollut. 2015, 197, 187– 194,  DOI: 10.1016/j.envpol.2014.11.030
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      Particulate Matter deposition on Quercus ilex leaves in an industrial city of central Italy
      Sgrigna, G.; Saeboe, A.; Gawronski, S.; Popek, R.; Calfapietra, C.
      Environmental Pollution (Oxford, United Kingdom) (2015), 197 (), 187-194CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
      A no. of studies have focused on urban trees to understand their mitigation capacity of air pollution. In this study particulate matter (PM) deposition on Quercus ilex leaves was quant. analyzed in four districts of the City of Terni (Italy) for three periods of the year. Fine (between 0.2 and 2.5 μm) and Large (between 2.5 and 10 μm) PM fractions were analyzed. Mean PM deposition value on Quercusilex leaves was 20.6 μg cm-2. Variations in PM deposition correlated with distance to main roads and downwind position relatively to industrial area. Epicuticular waxes were measured and related to accumulated PM. For Fine PM deposited in waxes we obsd. a higher value (40% of total Fine PM) than Large PM (4% of total Large PM). Results from this study allow to increase our understanding about air pollution interactions with urban vegetation and could be hopefully taken into account when guidelines for local urban green management are realized.
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    29. 29
      De Nicola, F.; Maisto, G.; Prati, M. V.; Alfani, A. Leaf Accumulation of Trace Elements and Polycyclic Aromatic Hydrocarbons (PAHs) in Quercus Ilex L. Environ. Pollut. 2008, 153 (2), 376– 383,  DOI: 10.1016/j.envpol.2007.08.008
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      29
      Leaf accumulation of trace elements and polycyclic aromatic hydrocarbons (PAHs) in Quercus ilex L.
      De Nicola, F.; Maisto, G.; Prati, M. V.; Alfani, A.
      Environmental Pollution (Amsterdam, Netherlands) (2008), 153 (2), 376-383CODEN: ENPOEK; ISSN:0269-7491. (Elsevier B.V.)
      Quercus ilex L. leaves were collected 4 times in 1 yr at 6 urban sites and 1 remote area to det. trace element and PAH accumulation through concomitant analyses of unwashed and water-washed leaves. Both unwashed and washed leaves showed the highest amts. of trace elements and PAHs in the urban area. Unwashed leaves showed greater differences between urban and remote areas and among the urban sites than washed leaves for trace element and PAH concns. Water-washing resulted in a significant (P <0.001) decrease in leaf concns. of Cr, Cu, Fe, Pb, V, and Zn. By contrast, Cd and total PAH concns. showed no differences between unwashed and washed leaves.
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      Sawidis, T.; Breuste, J.; Mitrovic, M.; Pavlovic, P.; Tsigaridas, K. Trees as Bioindicator of Heavy Metal Pollution in Three European Cities. Environ. Pollut. 2011, 159 (12), 3560– 3570,  DOI: 10.1016/j.envpol.2011.08.008
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      Trees as bioindicator of heavy metal pollution in three European cities
      Sawidis, T.; Breuste, J.; Mitrovic, M.; Pavlovic, P.; Tsigaridas, K.
      Environmental Pollution (Oxford, United Kingdom) (2011), 159 (12), 3560-3570CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
      Concns. of four heavy metals were detd. in tree leaves and bark collected from polluted and non-polluted areas of three European cities (Salzburg, Belgrade and Thessaloniki) for a comparative study. Platanus orientalis L. and Pinus nigra Arn., widespread in urban northern and southern Europe, were tested for their suitability for air quality biomonitoring. Leaves and barks were collected uniformly of an initial quantity of about 30 g of each sample. Anal. was accomplished by electrothermal at. absorption spectrometry after total digestion. Site-dependent variations were found with the highest concn. level measured in Belgrade, followed by Thessaloniki and Salzburg. A higher accumulation of heavy metals was found in bark compared to leaves. Pine tree bark, accumulating higher concns. of trace metals compared to plane tree bark, shows a higher efficiency as bioindicator for urban pollution. Both indicator species are suitable for comparative studies on bioindication of urban air pollution. Oriental plane (Platanus orientalis L.) and Austrian pine (Pinus nigra Arn.), widespread in urban northern and southern Europe, are suitable for comparative biomonitoring of urban air pollution.
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    31. 31
      Ristorini, M.; Baldacchini, C.; Massimi, L.; Sgrigna, G.; Calfapietra, C. Innovative Characterization of Particulate Matter Deposited on Urban Vegetation Leaves through the Application of a Chemical Fractionation Procedure. Int. J. Environ. Res. Public Health 2020, 17 (16), 5717– 19,  DOI: 10.3390/ijerph17165717
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      Innovative characterization of particulate matter deposited on urban vegetation leaves through the application of a chemical fractionation procedure
      Ristorini, Martina; Baldacchini, Chiara; Massimi, Lorenzo; Sgrigna, Gregorio; Calfapietra, Carlo
      International Journal of Environmental Research and Public Health (2020), 17 (16), 5717CODEN: IJERGQ; ISSN:1660-4601. (MDPI AG)
      In this study, we have evaluated the efficiency of a chem. fractionation procedure for the characterization of both the water-sol. and the insol. fraction of the main elemental components of particulate matter (PM) deposited on urban leaves. The proposed anal. approach is based on the chem. anal. of leaf washing solns. and membrane filters used for their filtration. The ionic concn. of leaf washing solns. was compared with their elec. cond., making it a valuable proxy for the quantification of the water-sol. and ionic fraction of leaf deposited PM. The chem. compn. of both the water-sol. and the insol. fraction of PM, resulting from this fractionation procedure, was compared with results obtained by SEM coupled with energy-dispersed X-Rays spectroscopy (SEM/EDX) and processed through chemometrics. Results obtained proved that the proposed approach is able to provide an estn. of total leaf deposited PM and it is highly reliable for the evaluation of the emission impact of different PM sources, being able to increase the selectivity of PM elemental components as specific source tracers; consequently providing useful information also for the assessment of human health risks.
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    32. 32
      Castanheiro, A.; Hofman, J.; Nuyts, G.; Joosen, S.; Spassov, S.; Blust, R.; Lenaerts, S.; De Wael, K.; Samson, R. Leaf Accumulation of Atmospheric Dust: Biomagnetic, Morphological and Elemental Evaluation Using SEM, ED-XRF and HR-ICP-MS. Atmos. Environ. 2020, 221, 117082,  DOI: 10.1016/j.atmosenv.2019.117082
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      Leaf accumulation of atmospheric dust: Biomagnetic, morphological and elemental evaluation using SEM, ED-XRF and HR-ICP-MS
      Castanheiro, Ana; Hofman, Jelle; Nuyts, Gert; Joosen, Steven; Spassov, Simo; Blust, Ronny; Lenaerts, Silvia; De Wael, Karolien; Samson, Roeland
      Atmospheric Environment (2020), 221 (), 117082CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
      Atm. dust deposition on plants enables the collection of site-specific particulate matter (PM). Knowing the morphol. and compn. of PM aids in disclosing their emitting sources as well as the assocd. human health risk. Therefore, this study aimed for a leaf-level holistic anal. of dust accumulation on plant leaves. Plant species (ivy and strawberry) with distinct leaf macro- and micro-morphol. were exposed during 3 mo at a moderate road traffic site in Antwerp, Belgium. Leaves collected every three weeks were analyzed for their magnetic signature, morphol. and elemental content, by a combination of techniques (biomagnetic analyses, ED-XRF, HR-ICP-MS, SEM). Dust accumulation on the leaves was obsd. both visually (SEM) and magnetically, while the metal enrichment was limited (only evident for Cr) and more variable over time. Temporal dynamics during the second half of the exposure period, due to pptn. events and redn. of atm. pollution input, were evidenced in our results (elements/magnetically/SEM). Ivy accumulated more dust than strawberry leaves and seemed less susceptible to wash-off, even though strawberry leaves contain trichomes and a rugged micromorphol., leaf traits considered to be important for capturing PM. The magnetic enrichment (in small-grained, SD/PSD magnetite particles), on the other hand, was not species-specific, indicating a common contributing source. Variations in pollution contributions, meteorol. phenomena, leaf traits, particle deposition (and encapsulation) vs. micronutrients depletion, are discussed in light of the conducted monitoring campaign. Although not completely elucidative, the complex, multifactorial process of leaf dust accumulation can better be understood through a combination of techniques.
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      Baldacchini, C.; Sgrigna, G.; Clarke, W.; Tallis, M.; Calfapietra, C. An Ultra-Spatially Resolved Method to Quali-Quantitative Monitor Particulate Matter in Urban Environment. Environ. Sci. Pollut. Res. 2019, 26 (18), 18719– 18729,  DOI: 10.1007/s11356-019-05160-8
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      An ultra-spatially resolved method to quali-quantitative monitor particulate matter in urban environment
      Baldacchini, Chiara; Sgrigna, Gregorio; Clarke, Woody; Tallis, Matthew; Calfapietra, Carlo
      Environmental Science and Pollution Research (2019), 26 (18), 18719-18729CODEN: ESPLEC; ISSN:0944-1344. (Springer)
      Monitoring the amt. and compn. of airborne particulate matter (PM) in the urban environment is a crucial aspect to guarantee citizen health. To focus the action of stakeholders in limiting air pollution, fast and highly spatially resolved methods for monitoring PM are required. Recently, the trees' capability in capturing PM inspired the development of several methods intended to use trees as biomonitors; this results in the potential of having an ultra-spatially resolved network of low-cost PM monitoring stations throughout cities, without the needing of on-site stations. Within this context, we propose a fast and reliable method to qual. and quant. characterize the PM present in urban air based on the anal. of tree leaves by SEM combined with X-ray spectroscopy (SEM/EDX). We have tested our method in the Real Bosco di Capodimonte urban park (Naples, Italy), by collecting leaves from Quercus ilex trees along transects parallel to the main wind directions. The coarse (PM10-2.5) and fine (PM2.5) amts. obtained per unit leaf area have been validated by weighting the PM washed from leaves belonging to the same sample sets. PM size distribution and elemental compn. match appropriately with the known pollution sources in the sample sites (i.e., traffic and marine aerosol). The proposed methodol. will then allow the use of the urban forest as an ultra-spatially resolved PM monitoring network, also supporting the work of urban green planners and stakeholders.
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      Guidolotti, G.; Calfapietra, C.; Pallozzi, E.; De Simoni, G.; Esposito, R.; Mattioni, M.; Nicolini, G.; Matteucci, G.; Brugnoli, E. Promoting the Potential of Flux-Measuring Stations in Urban Parks: An Innovative Case Study in Naples, Italy. Agric. For. Meteorol. 2017, 233, 153– 162,  DOI: 10.1016/j.agrformet.2016.11.004
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      Pallozzi, E.; Guidolotti, G.; Mattioni, M.; Calfapietra, C. Particulate Matter Concentrations and Fluxes within an Urban Park in Naples. Environ. Pollut. 2020, 266, 115134,  DOI: 10.1016/j.envpol.2020.115134
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      Particulate matter concentrations and fluxes within an urban park in Naples
      Pallozzi, E.; Guidolotti, G.; Mattioni, M.; Calfapietra, C.
      Environmental Pollution (Oxford, United Kingdom) (2020), 266 (Part_3), 115134CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
      Airborne particulate matter can represent a serious issue for human health, esp. in densely populated urban areas. Moreover, the inhalation of particulate can be more harmful with decreasing particles diam. Vegetation can provide many ecosystem services to the citizens, including the removal of many different pollutants in the air, but while the effect on many gaseous compds. has already been widely proved, the capability of particulate matter (PM) sequestration driven by vegetation and its resulting benefit on air quality has not been deeply investigated yet at larger spatial scale, esp. in Mediterranean environment. This study was conducted in the Real Bosco di Capodimonte, a green area of about 125 ha located inside the urban area of Naples (Italy) contg. different species typical of the Mediterranean forest ecosystem. To better understand the interaction between PM and the park area, we measured fluxes of PM10, PM2.5 and PM1 with a fast acquisition analyzer, according to the Eddy Covariance technique. We found that the particle deposition was higher during the central hours of the day and it was more evident for smaller size particles. Furthermore, the daily PM fluxes found accorded with evapotranspiration and carbon sequestration operated by plants, suggesting a possible active role of vegetation on the particulate deposition.
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      Christen, A. Atmospheric Measurement Techniques to Quantify Greenhouse Gas Emissions from Cities. Urban Clim. 2014, 10 (P2), 241– 260,  DOI: 10.1016/j.uclim.2014.04.006
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      Ward, H. C.; Kotthaus, S.; Grimmond, C. S. B.; Bjorkegren, A.; Wilkinson, M.; Morrison, W. T. J.; Evans, J. G.; Morison, J. I. L.; Iamarino, M. Effects of Urban Density on Carbon Dioxide Exchanges: Observations of Dense Urban, Suburban and Woodland Areas of Southern England. Environ. Pollut. 2015, 198, 186– 200,  DOI: 10.1016/j.envpol.2014.12.031
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      Effects of urban density on carbon dioxide exchanges: Observations of dense urban, suburban and woodland areas of southern England
      Ward, H. C.; Kotthaus, S.; Grimmond, C. S. B.; Bjorkegren, A.; Wilkinson, M.; Morrison, W. T. J.; Evans, J. G.; Morison, J. I. L.; Iamarino, M.
      Environmental Pollution (Oxford, United Kingdom) (2015), 198 (), 186-200CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
      Anthropogenic and biogenic controls on the surface-atm. exchange of CO2 are explored for three different environments. Similarities are seen between suburban and woodland sites during summer, when photosynthesis and respiration det. the diurnal pattern of the CO2 flux. In winter, emissions from human activities dominate urban and suburban fluxes; building emissions increase during cold weather, while traffic is a major component of CO2 emissions all year round. Obsd. CO2 fluxes reflect diurnal traffic patterns (busy throughout the day (urban); rush-hour peaks (suburban)) and vary between working days and non-working days, except at the woodland site. Suburban vegetation offsets some anthropogenic emissions, but 24-h CO2 fluxes are usually pos. even during summer. Observations are compared to estd. emissions from simple models and inventories. Annual CO2 exchanges are significantly different between sites, demonstrating the impacts of increasing urban d. (and decreasing vegetation fraction) on the CO2 flux to the atm.
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      Rannik, U.; Aubinet, M.; Kurbanmuradov, O.; Sabelfeld, K. K.; Markkanen, T.; Vesala, T. Footprint Analysis for Measurements over a Heterogeneous Forest. Boundary-Layer Meteorol. 2000, 97 (1), 137– 166,  DOI: 10.1023/A:1002702810929
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      Järvi, L.; Rannik, U.; Kokkonen, T. V.; Kurppa, M.; Karppinen, A.; Kouznetsov, R. D.; Rantala, P.; Vesala, T.; Wood, C. R. Uncertainty of Eddy Covariance Flux Measurements over an Urban Area Based on Two Towers. Atmos. Meas. Tech. 2018, 11 (10), 5421– 5438,  DOI: 10.5194/amt-11-5421-2018
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      Uncertainty of eddy covariance flux measurements over an urban area based on two towers
      Jarvi, Leena; Rannik, Ullar; Kokkonen, Tom V.; Kurppa, Mona; Karppinen, Ari; Kouznetsov, Rostislav D.; Rantala, Pekka; Vesala, Timo; Wood, Curtis R.
      Atmospheric Measurement Techniques (2018), 11 (10), 5421-5438CODEN: AMTTC2; ISSN:1867-8548. (Copernicus Publications)
      The eddy covariance (EC) technique is the most direct method for measuring the exchange between the surface and the atm. in different ecosystems. Thus, it is commonly used to get information on air pollutant and greenhouse gas emissions, and on turbulent heat transfer. Typically an ecosystem is monitored by only one single EC measurement station at a time, making the ecosystem-level flux values subject to random and systematic uncertainties. Furthermore, in urban ecosystems we often have no choice but to conduct the single-point measurements in non-ideal locations such as close to buildings and/or in the roughness sublayer, bringing further complications to data anal. and flux estns. In order to tackle the question of how representative a single EC measurement point in an urban area can be, two identical EC systems - measuring momentum, sensible and latent heat, and carbon dioxide fluxes - were installed on each side of the same building structure in central Helsinki, Finland, during July 2013-Sept. 2015. The main interests were to understand the sensitivity of the vertical fluxes on the single measurement point and to est. the systematic uncertainty in annual cumulative values due to missing data if certain, relatively wide, flow-distorted wind sectors are disregarded. The momentum and measured scalar fluxes respond very differently to the distortion caused by the building structure. The momentum flux is the most sensitive to the measurement location, whereas scalar fluxes are less impacted. The flow distortion areas of the two EC systems (40-150 and 230-340°) are best detected from the mean-wind-normalized turbulent kinetic energy, and outside these areas the median relative random uncertainties of the studied fluxes measured by one system are between 12 % and 28 %. Different gapfilling methods with which to yield annual cumulative fluxes show how using data from a single EC measurement point can cause up to a 12 % (480 g C m-2) underestimation in the cumulative carbon fluxes as compared to combined data from the two systems. Combining the data from two EC systems also increases the fraction of usable half-hourly carbon fluxes from 45 % to 69 % at the annual level. For sensible and latent heat, the resp. underestimations are up to 5 % and 8 % (0.094 and 0.069 TJ m-2). The obtained random and systematic uncertainties are in the same range as obsd. in vegetated ecosystems. We also show how the commonly used data flagging criteria in natural ecosystems, kurtosis and skewness, are not necessarily suitable for filtering out data in a densely built urban environment. The results show how the single measurement system can be used to derive representative flux values for central Helsinki, but the addn. of second system to other side of the building structure decreases the systematic uncertainties. Comparable results can be expected in similarly dense city locations where no large directional deviations in the source area are seen. In general, the obtained results will aid the scientific community by providing information about the sensitivity of EC measurements and their quality flagging in urban areas.
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      Hollinger, D. Y.; Aber, J.; Dail, B.; Davidson, E. A.; Goltz, S. M.; Hughes, H.; Leclerc, M. Y.; Lee, J. T.; Richardson, A. D.; Rodrigues, C.; Scott, N. A.; Achuatavarier, D.; Walsh, J. Spatial and Temporal Variability in Forest-Atmosphere CO2 Exchange. Glob. Chang. Biol. 2004, 10 (10), 1689– 1706,  DOI: 10.1111/j.1365-2486.2004.00847.x
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      Sgrigna, G.; Baldacchini, C.; Esposito, R.; Calandrelli, R.; Tiwary, A.; Calfapietra, C. Characterization of Leaf-Level Particulate Matter for an Industrial City Using Electron Microscopy and X-Ray Microanalysis. Sci. Total Environ. 2016, 548–549, 91– 99,  DOI: 10.1016/j.scitotenv.2016.01.057
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      Science of the Total Environment (2016), 548-549 (), 91-99CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
      This study reports application of monitoring and characterization protocol for particulate matter (PM) deposited on tree leaves, using Quercus ilex as a case study species. The study area is located in the industrial city of Terni in central Italy, with high PM concns. Four trees were selected as representative of distinct pollution environments based on their proximity to a steel factory and a street. Wash off from leaves onto cellulose filters were characterized using SEM and energy dispersive X-ray spectroscopy, inferring the assocns. between particle sizes, chem. compn., and sampling location. Modeling of particle size distributions showed a tri-modal fingerprint, with the three modes centered at 0.6 (factory related), 1.2 (urban background), and 2.6 μm (traffic related). Chem. detection identified 23 elements abundant in the PM samples. Principal component anal. recognized iron and copper as source-specific PM markers, attributed mainly to industrial and heavy traffic pollution resp. Upscaling these results on leaf area basis provided a useful indicator for strategic evaluation of harmful PM pollutants using tree leaves.
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      Baldocchi, D. D. Assessing the Eddy Covariance Technique for Evaluating Carbon Dioxide Exchange Rates of Ecosystems: Past, Present and Future. Glob. Chang. Biol. 2003, 9 (4), 479– 492,  DOI: 10.1046/j.1365-2486.2003.00629.x
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      Hofman, J.; Wuyts, K.; Van Wittenberghe, S.; Samson, R. On the Temporal Variation of Leaf Magnetic Parameters: Seasonal Accumulation of Leaf-Deposited and Leaf-Encapsulated Particles of a Roadside Tree Crown. Sci. Total Environ. 2014, 493, 766– 772,  DOI: 10.1016/j.scitotenv.2014.06.074
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      On the temporal variation of leaf magnetic parameters: Seasonal accumulation of leaf-deposited and leaf-encapsulated particles of a roadside tree crown
      Hofman, Jelle; Wuyts, Karen; Van Wittenberghe, Shari; Samson, Roeland
      Science of the Total Environment (2014), 493 (), 766-772CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
      Understanding the accumulation behavior of atm. particles inside tree leaves is of great importance for the interpretation of biomagnetic monitoring results. This study evaluated the temporal variation of the satn. isothermal remanent magnetization (SIRM) of leaves of a roadside urban Platanus × acerifolia Willd. tree in Antwerp, Belgium. This study examd. the seasonal development of the total leaf SIRM signal as well as the leaf-encapsulated fraction of the deposited dust, by washing the leaves before biomagnetic anal. On av. 38% of the leaf SIRM signal was exhibited by the leaf-encapsulated particles. Significant correlations were found between the SIRM and the cumulative daily av. atm. PM10 and PM2.5 measurements. A steady increase of the SIRM throughout the in-leaf season was obsd. endorsing the applicability of biomagnetic monitoring as a proxy for the time-integrated PM exposure of urban tree leaves. Strongest correlations were obtained for the SIRM of the leaf-encapsulated particles which confirms the dynamic nature of the leaf surface-accumulated particles.
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      Popek, R.; Haynes, A.; Przybysz, A.; Robinson, S. A. How Much Doesweather Matter? Effects of Rain and Wind on PM Accumulation by Four Species of Australian Native Trees. Atmosphere (Basel). 2019, 10 (10), 1– 14.  DOI: 10.3390/atmos10100633 .
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      Ould-Dada, Z.; Baghini, N. M. Resuspension of Small Particles from Tree Surfaces. Atmos. Environ. 2001, 35 (22), 3799– 3809,  DOI: 10.1016/S1352-2310(01)00161-3
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      Resuspension of small particles from tree surfaces
      Ould-Dada, Zitouni; Baghini, Nasser M.
      Atmospheric Environment (2001), 35 (22), 3799-3809CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Science Ltd.)
      A detailed study of the resuspension of 1.85-μm MMAD (mass median aerodynamic diam.) silica particles from five horizontal layers within a small-scale spruce canopy was carried out in a wind tunnel in which saplings were exposed to a const. free stream wind speed of 5 m/s. This provided quant. ests. of the potential for a tree canopy contaminated with an aerosol deposit to provide (i) an airborne inhalation hazard within the forest environment and (ii) a secondary source of airborne contamination after an initial deposition event. Resuspension occurred with a flux of 1.05 × 10-7 g/m2-s from spruce saplings initially contaminated at a level of 4.1 × 10-2 g/m2. An av. resuspension rate (Λ) of 4.88 × 10-7/s was obtained for the canopy as a whole. Values of Λ were significantly different (ANOVA, p<0.001) between canopy layers, and Λ was markedly greater at the top of the canopy than lower down, although there was a slight increase in Λ at the base of the canopy. The resuspended silica particles deposited onto the soil surface at an av. rate of about 5.3 × 10-8 μg/cm2-s. It is concluded that resuspension under wind velocities similar to that used in the reported expts. is likely to pose a relatively small inhalation hazard to humans and a relatively minor source of secondary contamination of adjacent areas. Furthermore, resuspension rates are likely to diminish rapidly with time. The results are discussed in relation to the growing interest in tree planting schemes in urban areas to reduce the impacts of air pollution.
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      Järvi, L.; Rannik, Ü.; Mammarella, I.; Sogachev, A.; Aalto, P. P.; Keronen, P.; Siivola, E.; Kulmala, M.; Vesala, T. Annual Particle Flux Observations over a Heterogeneous Urban Area. Atmos. Chem. Phys. 2009, 9 (20), 7847– 7856,  DOI: 10.5194/acp-9-7847-2009
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      Annual particle flux observations over a heterogeneous urban area
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      Atmospheric Chemistry and Physics (2009), 9 (20), 7847-7856CODEN: ACPTCE; ISSN:1680-7316. (Copernicus Publications)
      Long-term eddy covariance particle no. flux measurements for the diam. range 6 nm to 5 μm were performed at the SMEAR III station over an urban area in Helsinki, Finland. The heterogeneity of the urban measurement location allowed us to study the effect of different land-use classes in different wind directions on the measured fluxes. The particle no. fluxes were highest in the direction of a local road on weekdays, with a daytime median flux of 0.8 × 109 m-2 s-1. The particle fluxes showed a clear dependence on traffic rates and on the mixing conditions of the boundary layer. The measurement footprint was estd. by the use of both numerical and anal. models. Using the crosswind integrated form of the footprint function, we estd. the emission factor for the mixed vehicle fleet, yielding a median particle no. emission factor per vehicle of 3.0 × 1014 # km-1. Particle fluxes from the vegetated area were the lowest with daytime median fluxes below 0.2 × 109 m-2 s-1. During weekends and nights, the particle fluxes were low from all land use sectors being in the order of 0.02-0.1 × 109 m-2 s-1. On an annual scale the highest fluxes were measured in winter, when emissions from stationary combustion sources are also highest. Particle no. fluxes were compared with the simultaneously measured CO2 fluxes and similarity in their sources was distinguishable. For CO2, the median emission factor of vehicles was estd. to be 370 g km-1.
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      Ueyama, M.; Ando, T. Diurnal, Weekly, Seasonal, and Spatial Variabilities in Carbon Dioxide Flux in Different Urban Landscapes in Sakai, Japan. Atmos. Chem. Phys. 2016, 16 (22), 14727– 14740,  DOI: 10.5194/acp-16-14727-2016
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      Diurnal, weekly, seasonal, and spatial variabilities in carbon dioxide flux in different urban landscapes in Sakai, Japan
      Ueyama, Masahito; Ando, Tomoya
      Atmospheric Chemistry and Physics (2016), 16 (22), 14727-14740CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      To evaluate CO2 emissions in urban areas and their temporal and spatial variability, continuous measurements of CO2 fluxes were conducted using the eddy covariance method at three locations in Sakai, Osaka, Japan. Based on the flux footprint at the measurement sites, CO2 fluxes from the three sites were partitioned into five datasets representing a dense urban center, a moderately urban area, a suburb, an urban park, and a rural area. A distinct biol. uptake of CO2 was obsd. in the suburb, urban park, and rural areas in the daytime, whereas high emissions were obsd. in the dense and moderate urban areas in the daytime. Weekday CO2 emissions in the dense urban center and suburban area were approx. 50 % greater than emissions during weekends and holidays, but the other landscapes did not exhibit a clear weekly cycle. Seasonal variations in the urban park, rural area, and suburban area were influenced by photosynthetic uptake, exhibiting the lowest daily emissions or even uptake during the summer months. In contrast, the dense and moderately urban areas emitted CO2 in all seasons. CO2 emissions in the urban areas were high in the winter and summer months, and they significantly increased with the increase in air temp. in the summer and the decrease in air temp. in the winter. Irresp. of the land cover type, all urban landscapes measured in this study acted as net annual CO2 sources, with emissions ranging from 0.5 to 4.9 kg C m-2 yr-1. The magnitude of the annual CO2 emissions was neg. correlated with the green fraction; areas with a smaller green fraction had higher annual CO2 emissions. Upscaled flux estd. based on the green fraction indicated that the emissions for the entire city were 3.3 kg C m-2 yr-1, which is equiv. to 0.5 Tg C yr-1 or 1.8 Mt CO2 yr-1, based on the area of the city (149.81 km2). A network of eddy covariance measurements is useful for characterizing the spatial and temporal variations in net CO2 fluxes from urban areas. Multiple methods would be required to evaluate the rationale behind the fluxes and overcome the limitations in the future.
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      Sun, F.; Yin, Z.; Lun, X.; Zhao, Y.; Li, R.; Shi, F.; Yu, X. Deposition Velocity of PM2.5 in the Winter and Spring above Deciduous and Coniferous Forests in Beijing, China. PLoS One 2014, 9 (5), e97723– 11,  DOI: 10.1371/journal.pone.0097723
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      Deposition velocity of PM2.5 in the winter and spring above deciduous and coniferous forests in Beijing, China
      Sun, Fengbin; Yin, Zhe; Lun, Xiaoxiu; Zhao, Yang; Li, Renna; Shi, Fangtian; Yu, Xinxiao
      PLoS One (2014), 9 (5), e97723/1-e97723/11, 11 pp.CODEN: POLNCL; ISSN:1932-6203. (Public Library of Science)
      To est. the deposition effect of PM2.5 (particle matter with aerodynamic diam. <2.5 μm) in forests in northern China, we used the gradient method to measure the deposition velocity of PM2.5 during the winter and spring above a deciduous forest in Olympic Forest Park and above a coniferous forest in Jiufeng National Forest Park. Six aerosol samplers were placed on two towers at each site at heights of 9, 12 and 15 m above the ground surface. The sample filters were exchanged every four hours at 6:00 AM, 10:00 AM, 2:00 PM, 6:00 PM, 10:00 PM, and 2:00 AM. The daytime and nighttime deposition velocities in Jiufeng Park and Olympic Park were compared in this study. The Feb. deposition velocities in Jiufeng Park were 1.2 ± 1.3 and 0.7 ± 0.7 cm s-1 during the day and night, resp. The May deposition velocities in Olympic Park were 0.9 ± 0.8 and 0.4 ± 0.5 cm s-1 during the day and night, resp. The May deposition velocities in Jiufeng Park were 1.1 ± 1.2 and 0.6 ± 0.5 cm s-1 during the day and night, resp. The deposition velocities above Jiufeng National Forest Park were higher than those above Olympic Forest Park. The measured values were smaller than the simulated values obtained by the Ruijgrok et al. (1997) and Wesely et al. (1985) models. However, the reproducibility of the Ruijgrok et al. (1997) model was better than that of the Wesely et al. (1985) model. The Hicks et al. (1977) model was used to analyze addnl. forest parameters to calc. the PM2.5 deposition, which could better reflect the role of the forest in PM2.5 deposition.
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      Xu, X.; Xia, J.; Gao, Y.; Zheng, W. Additional Focus on Particulate Matter Wash-off Events from Leaves Is Required: A Review of Studies of Urban Plants Used to Reduce Airborne Particulate Matter Pollution. Urban Forestry and Urban Greening.; Elsevier GmbH, February 1, 2020.  DOI: 10.1016/j.ufug.2019.126559 .
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      Zhang, L.; Zhang, Z.; Chen, L.; McNulty, S. An Investigation on the Leaf Accumulation-Removal Efficiency of Atmospheric Particulate Matter for Five Urban Plant Species under Different Rainfall Regimes. Atmos. Environ. 2019, 208, 123– 132,  DOI: 10.1016/j.atmosenv.2019.04.010
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      An investigation on the leaf accumulation-removal efficiency of atmospheric particulate matter for five urban plant species under different rainfall regimes
      Zhang, Lu; Zhang, Zhiqiang; Chen, Lixin; McNulty, Steven
      Atmospheric Environment (2019), 208 (), 123-132CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
      Urban trees and forests are widely used as biol. filters to combat the airborne particulate matter (PM). Pptn. washing PM off from plants is regarded as filter cleaning, which is a key factor for recovering the function of foliar PM filtering. However, it is uncertain on how much PM can be total filtered by urban trees due to lack of understanding about how PM deposition, removal, resuspension and redeposition interact with species and rainfall variability. For this reason, we developed a study to det. foliar PM removal amt. and rate of different sizes for five plant species commonly used for urban greening by simulated different rainfall regimes. Our specific objectives were to: (1) explore the difference in PM removal between different plant species and different rainfall patterns; (2) understand the response of foliar PM removal as a function of rainfall characteristics; and (3) quantify the relationship between foliar PM removal rate and leaf coarseness. Results showed that significant differences (P < 0.05) in PM removal amt. and rate were found not only between different species within the same rainfall pattern, but also between different rainfall patterns for the same species. PM removal rates from the leaf surface were significantly correlated with rainfall intensity (P < 0.01). Different size PM cumulative removal rate exhibited an exponential loss with rainfall duration (P < 0.01). For smooth leaf surfaces, long duration-low intensity rainfall could increase PM removal rate while for rough leaf surfaces, short duration-high intensity rainfall could achieve a larger removal rate using the same amt. of total rainfall. Addnl., more PM was removed by rainfall than that by water washing. The findings from this study have implications for better estg. long-term air purifn. potential of urban plants, and for air phytoremediation planning in urban areas.
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      Wedding, J.; Carlson, R.; Stukel, J.; Bazzaz, F. Aerosol Deposition on Plant Leaves. Water, Air, Soil Pollut. 1977, 7 (4), 545– 550,  DOI: 10.1007/BF00285551
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      Aerosol deposition on plant leaves
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      Water, Air, and Soil Pollution (1977), 7 (4), 545-50CODEN: WAPLAC; ISSN:0049-6979.
      An aerosol generator and wind tunnel system designed for use in aerosol deposition are described. Gross deposition on rough pubescent leaves was nearly seven times greater than on smooth, waxy leaves. Results suggest that aerosol deposition, on a per unit area basis, for single horizontal streamlining leaves is similar to that for arrays of leaves under similar flow conditions. Wind reentrainment of PbCl2 particles was negligible while 2.54 cm of simulated rainfall was sufficient to remove 85% of recently applied aerosol.
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      Zhang, W.; Wang, B.; Niu, X. Relationship between Leaf Surface Characteristics and Particle Capturing Capacities of Different Tree Species in Beijing. Forests 2017, 8 (3), 92– 12,  DOI: 10.3390/f8030092
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      Lu, S.; Yang, X.; Li, S.; Chen, B.; Jiang, Y.; Wang, D.; Xu, L. Effects of Plant Leaf Surface and Different Pollution Levels on PM2.5 Adsorption Capacity. Urban For. Urban Green 2018, 34 (May), 64– 70,  DOI: 10.1016/j.ufug.2018.05.006
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      Hofman, J.; Wuyts, K.; Van Wittenberghe, S.; Brackx, M.; Samson, R. On the Link between Biomagnetic Monitoring and Leaf-Deposited Dust Load of Urban Trees: Relationships and Spatial Variability of Different Particle Size Fractions. Environ. Pollut. 2014, 189 (2014), 63– 72,  DOI: 10.1016/j.envpol.2014.02.020
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      On the link between biomagnetic monitoring and leaf-deposited dust load of urban trees: Relationships and spatial variability of different particle size fractions
      Hofman, Jelle; Wuyts, Karen; Van Wittenberghe, Shari; Brackx, Melanka; Samson, Roeland
      Environmental Pollution (Oxford, United Kingdom) (2014), 189 (), 63-72CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
      Biomagnetic monitoring of urban tree leaves has proven to be a good estimator of ambient particulate matter. We evaluated its relevancy by detg. leaf area normalized wt. (mg m-2) and SIRM (A) of leaf-deposited particles within three different size fractions (>10 μm, 3-10 μm and 0.2-3 μm) and the SIRM of the leaf-encapsulated particles. Results showed that throughout the in-leaf season, the trees accumulated on av. 747 mg m-2 of dust on their leaves, of which 74 mg m-2 was within the 0.2-10 μm (∼PM10) size range and 40 mg m-2 within the 0.2-3 μm (∼PM3) size range. A significant correlation between the SIRM and wt. of the surface-deposited particles confirms the potential of biomagnetic monitoring as a proxy for the amt. of leaf-deposited particles. Spatial variation of both SIRM and wt. throughout the street canyon suggests traffic and wind as key factors for resp. the source and distribution of urban particulates.
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      Leonard, R. J.; McArthur, C.; Hochuli, D. F. Particulate Matter Deposition on Roadside Plants and the Importance of Leaf Trait Combinations. Urban For. Urban Green 2016, 20, 249– 253,  DOI: 10.1016/j.ufug.2016.09.008
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      Grote, R.; Samson, R.; Alonso, R.; Amorim, J. H.; Cariñanos, P.; Churkina, G.; Fares, S.; Thiec, D.; Le; Niinemets, Ü.; Mikkelsen, T. N.; Paoletti, E.; Tiwary, A.; Calfapietra, C. Functional Traits of Urban Trees: Air Pollution Mitigation Potential. Front. Ecol. Environ. 2016, 14 (10), 543– 550,  DOI: 10.1002/fee.1426
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      Caneva, G.; Bartoli, F.; Zappitelli, I.; Savo, V. Street Trees in Italian Cities: Story, Biodiversity and Integration within the Urban Environment. Rend. Lincei. Sci. Fis. e Nat. 2020, 31, 411,  DOI: 10.1007/s12210-020-00907-9
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      Blanusa, T.; Fantozzi, F.; Monaci, F.; Bargagli, R. Leaf Trapping and Retention of Particles by Holm Oak and Other Common Tree Species in Mediterranean Urban Environments. Urban For. Urban Green. 2015, 14 (4), 1095– 1101,  DOI: 10.1016/j.ufug.2015.10.004
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      Zheng, G.; Li, P. Resuspension of Settled Atmospheric Particulate Matter on Plant Leaves Determined by Wind and Leaf Surface Characteristics. Environ. Sci. Pollut. Res. 2019, 26 (19), 19606– 19614,  DOI: 10.1007/s11356-019-05241-8
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      Resuspension of settled atmospheric particulate matter on plant leaves determined by wind and leaf surface characteristics
      Zheng Guiling; Li Peng
      Environmental science and pollution research international (2019), 26 (19), 19606-19614 ISSN:.
      Atmospheric particulate matter (APM) is temporarily settled on the leaf surface of plants and will return to the air via the resuspension process under certain meteorological conditions. How leaf surface characteristics affect the resuspension of settled APM on the leaf surface has been rarely studied. Therefore, the resuspension of APM after settling on plant leaves was analyzed using four common urban greening species, including Prunus triloba, Platanus acerifolia, Lonicera maackii, and Cercis chinensis. The results show that the leaf hair density has a significantly positive correlation with the maximum particulate matter (PM) retention and natural PM retention (p < 0.05). Under the same wind speed, the proportions of the resuspended PM that settled on the leaf surfaces of the four plant species increase with the wind blowing time. During the same wind blowing time, the resuspension rate of the settled PM on leaf surfaces of P. triloba, P. acerifolia, and L. maackii increase with the wind speed. The leaf hair and stomatal density is negatively correlated to the resuspension rate of PM under the wind speed of 1 m s(-1) (p < 0.05), and the stomatal density is also negatively correlated to the resuspension rate of PM under the wind speed of 5 m s(-1) for 10 min or 20 min (p < 0.05). However, as the wind speed further increase, the leaf characteristics are no longer correlated to the resuspension rate of PM (p > 0.05). These results indicate that when the wind force (wind speed + wind blowing time) is small, the stomatal density and leaf hair density have a significant effect on APM resuspension. When the wind force is large, the influence of leaf surface structure on APM resuspension becomes less profound. APM resuspension is comprehensively affected by the external wind and the leaf surface characteristics, and these two factors jointly determine the fate of the PM after it settles on leaves.
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    63. 63
      Pullman, M. R. Conifer PM2.5 Deposition and Re-Suspension in Wind and Rain Events, Cornell University: Ithaca, NY, United States, 2009.
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    64. 64
      Schaubroeck, T.; Deckmyn, G.; Neirynck, J.; Staelens, J.; Adriaenssens, S.; Dewulf, J.; Muys, B.; Verheyen, K. Multilayered Modeling of Particulate Matter Removal by a Growing Forest over Time, from Plant Surface Deposition to Washoff via Rainfall. Environ. Sci. Technol. 2014, 48 (18), 10785– 10794,  DOI: 10.1021/es5019724
      [ACS Full Text ACS Full Text], [CAS], Google Scholar
      64
      Multilayered Modeling of Particulate Matter Removal by a Growing Forest over Time, From Plant Surface Deposition to Washoff via Rainfall
      Schaubroeck, Thomas; Deckmyn, Gaby; Neirynck, Johan; Staelens, Jeroen; Adriaenssens, Sandy; Dewulf, Jo; Muys, Bart; Verheyen, Kris
      Environmental Science & Technology (2014), 48 (18), 10785-10794CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Airborne fine particulate matter (PM) is responsible for the most severe health effects induced by air pollution in Europe. Vegetation, particularly forests, can play a role in mitigating this pollution since they have large surface area to filter PM from air. Many studies solely focused on PM dry deposition to tree surfaces, but deposited PM can be resuspended to the air or may be washed off by pptn. dripping from plants to the soil. It is only the latter process that represents a net-removal from the atm. To quantify this removal all processes should be accounted for, which is done in the reported modeling framework. Hence, a multi-layered PM removal model for forest canopies was developed. This framework was integrated into an existing forest growth model to account for changes in PM removal efficiency during forest growth. A case study was performed on a Scots pine stand in Belgium, which for 2010 resulted in a dry deposition of 31 kg PM2.5/ha-yr from which 76% was resuspended and 24% was washed off. For different future emission redn. scenarios (2010-2030), with altered PM2.5 air concns., avoided health costs due to PM2.5 removal was estd. to be 915-1075 Euro/ha-yr. This model can even be used to predict nutrient input via PM matter, though further research is needed to improve and better validate the model.
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    The Supporting Information provides additional information on the representativeness of local weather and pollution stations compared to data measured by the EC tower, results of the multiple comparison of accumulated and net flux means (Turkey’s HSD) performing model simulations with a change in parameters, a comparison between the model and EC assessments in February 2018, and the sensitivity analysis of the deposition velocity considering a modification of parameters compared with EC results. The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.0c07679.

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