10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Simulating Secondary Organic Aerosol Formation in Cloudwater and Aerosols Using GAMMA 5.1
WILLIAM TSUI, Joseph Woo, V. Faye McNeill, Columbia University
Abstract Number: 70 Working Group: Aerosol Chemistry
Abstract Aqueous phase chemistry in cloudwater and aerosols is a known pathway of secondary organic aerosol (SOA) formation, yet its contribution in ambient conditions remains largely uncertain. In this study, we use Gas-Aerosol Model for Mechanism Analysis (GAMMA) version 5.1 to simulate SOA formation in particles alternating from aqueous aerosol to cloudwater. In acidic aerosols under low-NOx conditions, formation of tetrol and organosulfate products from isoprene epoxydiols (IEPOX) is a dominant process. However, when these acidic aerosols convert to cloudwater, the extent of this SOA formation pathway was seen to reduce significantly due to a decrease in aqueous H+ activity. Furthermore, particles initially in aerosol conditions for at least one hour were not observed to have organic acid formation upon transitioning to cloudwater. The lack of organic acid SOA is primarily due to the consumption of OH radicals in the formation of IEPOX under aerosol conditions, resulting in a depletion of radicals necessary for the generation of organic acids in cloudwater. Under high-NOx conditions, cloudwater concentrations were found to be less dependent on the amount of time as an aerosol in the beginning of the simulation than low-NOx conditions. Similar simulations of alternating cloudwater and aqueous aerosols are conducted using gas-phase concentrations from Whiteface Mountain as initial conditions.