Evaluation of Impacts of Haze Events on the Secondary Organic Aerosol Formation During the KORUS-AQ Campaign with CAMx-UNIPAR v1.4
GANGHAN KIM, Myoseon Jang, Yujin Jo, Azad Madhu, University of Florida
Abstract Number: 91
Working Group: Aerosol Physics
Abstract
Secondary Organic Aerosol (SOA) is a key component that forms the atmospheric organic particulate matter, affecting air quality associated with climate and human health. Despite the important aspect of SOA in air quality, SOA budgets in regional scales are still not well predicted because of missing precursors and the complexity of SOA formation mechanisms via multiphase reactions of various precursors under dynamic meteorological conditions. In particular, SOA simulations have been underpredicted during summer seasons under high humidity. Haze in urban areas is crucial because it can cause poor air quality due to the increased aqueous reaction of oxygenated organic products. In this study, the impact of the haze on SOA formation is simulated during the KORUS-AQ campaign in 2016 using the Unified Partitioning Aerosol-phase Reaction (UNIPAR) model in the Comprehensive Air quality Model with extensions (CAMx) platform. KORUS-AQ, an international cooperative air quality files study in South Korea, includes ground-based data and airborne data (NASA DC-8 and B-200 aircraft by NASA) to study the evolution of polluted cities (i.e., Seoul). In particular, the low-level transport/haze period appeared (24-31 May 2016) during KORUS-AQ, and significantly increased SOA formation. The UNIPAR model employed is capable of processing the multiphase reactions of precursors via multiphase partitioning of explicitly predicted oxygenated products and their reactions in organic and aqueous aerosol phases. The recently updated UNIPAR v1.4 employs model parameters to simulate SOA from 10 aromatics; naphthalene; and 3 biogenic for three major oxidation paths (OH radicals, ozone, and nitrate radicals) to process day and night SOA formation; and alkanes covering a wide range of carbon chain lengths (C9-C24) and branching ratios. For intermediate volatile precursors (long-chain alkanes), the chemical loss through a gas-particle partitioning process is considered. The CAMx-UNIPARv1.4 captures high SOA formation during the haze episode. The model predicts major SOA species, which are impacted by emission species, meteorological conditions (humidity, sunlight, and temperature), long-range transport, and day and night chemistry. The cities in South Korea are highly impacted by aromatic SOA followed by terpene and alkane while urban areas in the USA are affected by alkane and terpene as reported in the recent simulations for air quality in California and South USA. Isoprene SOA contributions were negligible during KORUS-AQ.