AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Effects of Relative Humidity and Aerosol Liquid Water on the Molecular Composition and Aging of Secondary Organic Aerosols
CYNTHIA WONG, Lauren Fleming, Julia Montoya-Aguilera, Sergey Nizkorodov, University of California, Irvine
Abstract Number: 863 Working Group: Aerosol Chemistry
Abstract Relative humidity (RH) and aerosol liquid water may have competing effects on secondary organic aerosol (SOA) formation. Elevated RH can alter the mechanism of gas-phase oxidation of volatile organic compounds, in which SOA are formed, and suppress oligomer formation in particles. Aerosol liquid water, on the other hand, can help oxidize the water soluble gases that partition into the aqueous phase, thereby increasing the particle mass concentration. After the particles are already formed, presence of water can alter the mechanisms of spontaneous and photochemical aging processes in particles. The goal of this work is to systematically explore the effects of water vapor and aerosol liquid water on the chemical composition of SOA during formation and aging. SOA from α-pinene ozonolysis were generated in a flow tube reactor in four different ways: in the presence and absence of ammonium sulfate seeds, and at <2% and 90% RH. Samples were either aged in dry or humid conditions for several days or analyzed immediately with direct analysis in real-time (DART) and electrospray ionization (ESI) mass spectrometry, to provide information about the chemical composition of SOA before and after aging. The patterns of peak intensities and observed molecular formulas were examined for evidence of water-driven chemistry. The results from this study should help decouple the effect of gaseous and liquid water on the chemical composition and properties of SOA, and ultimately improve our understanding of SOA formation and aging processes.