SOA Mass Formed via Multiphase Reactions of Hydrocarbons over the United States using CAMx-UNIPAR

YUJIN JO, Myoseon Jang, Azad Madhu, Jiwon Choi, Sanghee Han, University of Florida

     Abstract Number: 216
     Working Group: Aerosols Spanning Spatial Scales: Measurement Networks to Models and Satellites

Abstract
Secondary Organic Aerosol (SOA) contributes a significant portion of atmospheric organic aerosol. Therefore, the prediction of SOA budget in regional/global scales is important to correctly evaluate its impact on health and climate forcing. However, it is challenging to accurately predict SOA formation due to its complexity in oxidation paths of hydrocarbons (HCs) and reaction mechanisms. In this study, the SOA mass was predicted by the UNIfied Partitioning Aerosol Reaction (UNIPAR) model that can simulate multiphase reactions of various HCs. The model utilizes lumping species originating from semi-explicitly predicted gas products using emerging atmospheric oxidation mechanisms of a wide range of anthropogenic HCs (10 aromatics and linear/branched alkanes in different carbon-lengths) and biogenic HCs (isoprene, terpene, and sesquiterpene) with three oxidation paths (ozone, OH radicals, and nitrate radicals) to predict day and night SOA formation. Resulting lumping species are involved in their multiphase partitioning and heterogeneous chemistry to form nonvolatile oligomers in both organic and inorganic aqueous phases. UNIPAR is incorporated with the Comprehensive Air quality Model with extensions (CAMx) to process SOA formation in regional scales. CAMx-UNIPAR is applied to predict SOA mass in the southern U.S., where isoprene is abundant, between February and April in 2021. Our exploratory simulation suggests that SOA mass produced in the southern U.S. is dominated by alkane and terpene owing to the contribution of autoxidation of alkane in daytime and nighttime oxidations of terpene with nitrate radical and ozone. Seasonal variations of isoprene SOA are also simulated by capturing the isoprene emission and aqueous phase reactions of isoprene products that are influenced by humidity. Spatial distributions of anthropogenic SOA associated with aromatic and alkane can be affected by wind directions owing to the relatively long lifetime of their atmospheric oxidation, whereas those of biogenic SOA were nearly insensitive to wind directions.