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Long-term Aging of Secondary Organic Aerosols Derived from Monoterpenes in the Presence of Water Vapor and Liquid Water
CYNTHIA WONG, Daniel Vite, Sergey Nizkorodov, University of California, Irvine
Abstract Number: 247
Working Group: Aerosol Chemistry
Abstract
Secondary organic aerosols (SOA) can have a long lifetime in the atmosphere where they are exposed to different forms of water, including water vapor, aerosol liquid water, and cloud and fog droplets. In these environments, they can undergo a variety of chemical processes (i.e. hydrolysis) leading to changes in chemical composition. Previous studies have mainly focused on short term aging or hydrolysis of model organic compounds. This study investigates the stability of SOA compounds over longer time scales of days using SOA compounds from the ozonolysis of monoterpenes and exposing them to the different forms of aging scenarios where hydrolysis is likely. SOA samples were generated in an oxidative flow reactor and then impacted onto a foil substrate. Samples were then aged by exposure of water vapor for a couple of weeks or in an aqueous solution for several days and analyzed using direct infusion electrospray mass spectrometry (ESI-MS). Some of the MS scans were recorded in high-resolution mode permitting accurate formula assignments of the products. The results from the mass spectral analysis suggest that SOA compounds derived from the ozonolysis of monoterpenes were stable with respect to uncatalyzed hydrolysis for a period of up to two weeks. This demonstrates that hydrolysis is not likely to be a leading aging mechanism of SOA in humid environments. Aging by OH oxidation, acid-catalyzed aqueous reactions, and direct photochemistry occurs at faster rates than uncatalyzed hydrolysis.