Secondary organic aerosol (SOA) accounts for a large fraction of the total fine particle mass in the atmosphere. The formation of SOA takes place rapidly within hours after volatile organic compounds emissions, but they can undergo much slower physical and chemical processes throughout its lifetime in the atmosphere, which can be on the order of days to weeks. The acidity of atmospheric aerosols spans a wide range, with the most acidic particles having negative pH values, which can probe acid-catalyzed reactions. However, the impact of highly acidic conditions on aerosol chemical composition and aging processes remains uncertain. The goal of this work is to elucidate mechanisms and rates of acid-catalyzed aging of mixtures of SOA compounds. SOA samples were generated in a continuous flow reactor and collected using a foil substrate. Samples were extracted and aged by exposure to varying concentrations of aqueous sulfuric acid for two days. Analysis of fresh and aged samples was conducted using an ultra-liquid chromatography coupled with a photodiode array spectrophotometer and a high-resolution mass spectrometer to examine the light-absorbing properties and chemical composition of SOA before and after aging, respectively. We find that SOA aged in moderately acidic conditions leads to small changes in the aerosol composition, indicating no evidence of acid-catalyzed aging processes. On the other hand, SOA aged in a highly acidic environment resulted in significant changes in the chemical composition, including the formation of light-absorbing products and organosulfur compounds. The findings from this study will improve our understanding of SOA aging processes.

Long term aging of secondary organic aerosols under acidic conditions

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.