The effect of filter storage conditions on degradation of organic Aerosols.

Current practices involve wrapping organic aerosol (OA) filter samples with aluminum foil and storing in a freezer to avoid sample degradation prior to analysis. However, there is a lack of evidence supporting these practices. Here, we investigate the effect of thermal and photodegradation on toluene-combustion OA, pine-combustion OA, and ambient OA samples by storing them in petri dishes for one month at three different conditions: covered with aluminum foil and in a freezer (F), covered with aluminum foil at room temperature (RC), and uncovered at room temperature (RUC). We performed three types of analyses: thermal-optical measurements, electrospray ionization mass spectrometry, and UV-Vis spectroscopy. For all samples, we observed a mild reduction in the relatively volatile organic carbon fraction (OC1) in the RC and RUC conditions. We did not account for positive artifacts in this study, and therefore, this reduction was at least partially due to the evaporation of adsorbed vapors rather than particles. There was no evidence of significant systematic change in chemical composition relative to control for any of the storage conditions, except for loss of some small-molecular-size compounds in conditions RC and RUC for pine-combustion OA, likely due to evaporation. There was no evidence that photobleaching occurred in the RUC condition for any of the samples. On the contrary, we observed an increase in absorption in the RC and RUC conditions for pine-combustion OA, likely due to evaporation of small-molecular-size species with relatively weak absorption. Copyright © 2023 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]