Prolonged Dark Chemical Processes in Secondary Organic Aerosols on Filters and in Aqueous Solution

Secondary organic aerosol (SOA) represents a large fraction of atmospheric aerosol particles that significantly affect both the Earth’s climate and human health. Laboratory-generated SOA or ambient particles are routinely collected on filters for a detailed chemical analysis. Such filter sampling is prone to artifactual changes in composition during collection, storage, sample workup, and analysis. In this study, we investigate the chemical composition differences in SOA generated in the laboratory, kept at room temperature as aqueous extracts or on filters, and analyzed in detail after a storage time of a day and up to 4 weeks using liquid chromatography coupled to high-resolution mass spectrometry. We observe significantly different temporal concentration changes for monomers and oligomers in both extracts and on filters. In SOA aqueous extracts, many monomers increase in concentration over time, while many dimers decay at the same time. In contrast, on filters, we observe a strong and persistent concentration increase of many dimers and a decrease of many monomers. This study highlights artifacts arising from SOA chemistry occurring during storage, which should be considered when detailed organic aerosol compositions are studied. The particle-phase reactions on filters can also serve as a model system for atmospheric particle aging processes.

minutes.The 28-day old filter samples show a significant increase in both intensity and number of peaks compared to the fresh samples and aged extracts.A higher background (assigned to an unknown compound detected at m/z 305.0230, which is a constant background signal in our system) between peaks is observed for the stored extract samples.This increase in the base peak background leads to an increase of TIC signal in the stored extracts in Figure 2 (C), hence the signal intensity minus the background signal would be lower than the fresh samples.The corresponding timeseries for this isomer is given on the right.The corresponding timeseries for this isomer is given on the right.The corresponding timeseries for this isomer is given on the right.The corresponding timeseries for this isomer is given on the right.

S14
Highest intensity dimers in both fresh samples and 28-day old filter samples

Figure S 1 :
Figure S 1: (A) Setup used for the collection of laboratory-generated β-pinene secondary organic aerosol samples as described in Resch et al., (2023) 1 .(B)For "spiking" experiments a

Figure S 2 :
Figure S 2: (A) BPC representing fresh and aged filter and extract samples with m/z 80-1000.

Figure S 12 :
Figure S 12: EIC of the m/z 343.1757 dimer ester with highest intensity in the fresh samples.

Figure S 16 :
Figure S 16: EIC of the m/z 369.1913 dimer ester with highest intensity in the fresh samples.
Figure S 18: EIC of the m/z 337.2015 dimer ester with highest intensity in both the fresh and

Figure S 19 :
Figure S 19: EIC of the m/z 361.1499 dimer ester with highest intensity in both the fresh and

Figure S 22 :
Figure S 22: EIC of the m/z 470.2095 compound tentatively assigned as a trimer.The

Figure S 24 :
Figure S 24: EIC of the m/z 493.2294 compound tentatively assigned as a trimer.The

Figure S 27 Figure S 28
Figure S 27: (A) EIC of an isomer of diaterpenylic acid with m/z 189.0776 eluting at 6.96 min

Figure S 29 Figure
Figure S 29: (A) EIC of an isomer of the m/z 355.1757 proposed to be an ester of diaterpenylic

Table S 1
: Complete list containing Compound ID, observed m/z in negative polarity mode, Molecular Formula and literature references for all dimer esters investigated.Table S 2: List of oligomers analyzed.Molecular weight, tentative chemical formula, retention time and sample type of highest observed peak are given.

MW 344a / RT 13.51 min Figure
S 3: EIC of the m/z 339.1808 dimer ester with highest intensity in the 28-day old filter samples.The corresponding timeseries for this isomer is given on the right.Figure S 4: EIC of the m/z 343.1393 dimer ester with highest intensity in the 28-day old filter samples.The corresponding timeseries for this isomer is given on the right.
Retention time (min) Intensity (a.u.) MW 354 / RT 21.17 min Figure S 6: EIC of the m/z 353.1964 dimer ester with highest intensity in the 28-day old filter samples.The corresponding timeseries for this isomer is given on the right.MW 344b / RT 16.74 min Figure S 5: EIC of the m/z 343.1757 dimer ester with highest intensity in the 28-day old filter samples.The corresponding timeseries for this isomer is given on the right.Retention time (min) Intensity (a.u.) MW 368 / RT 13.83 min Figure S 7: EIC of the m/z 355.1757 dimer ester with highest intensity in the 28-day old filter samples.The corresponding timeseries for this isomer is given on the right.Figure S 8: EIC of the m/z 367.1757 dimer ester with highest intensity in the 28-day old filter samples.The corresponding timeseries for this isomer is given on the right.MW 372 / RT 14.87 min Figure S 9: EIC of the m/z 369.1913 dimer ester with highest intensity in the 28-day old filter samples.The corresponding timeseries for this isomer is given on the right.Figure S 10: EIC of the m/z 371.1706 dimer ester with highest intensity in the 28-day old filter samples.The corresponding timeseries for this isomer is given on the right.S10 Highest intensity dimers in fresh samples MW 344b / RT 16.34 min Figure S 11: EIC of the m/z 339.1808 dimer ester with highest intensity in the fresh samples.