Modeling Biogenic and Anthropogenic Secondary Organic Aerosol in China

A revised Community Multiscale Air Quality (CMAQ) model with updated secondary organic aerosol (SOA) yields and more detailed description of SOA formation from isoprene oxidation was applied to study the spatial and temporal distribution of SOA in China in the entire year of 2013. Predicted organic carbon (OC), elemental carbon and volatile organic compounds agreed favorably with observations at several urban areas, although the high OC concentrations in wintertime in Beijing were under-predicted. Predicted summer SOA was generally higher (10-15 µg m-3) due to large contributions of isoprene (country average, 61%). Wintertime SOA was slightly lower and was mostly due to emissions of alkane and aromatic compounds (51%). Contributions of monoterpenes SOA were relatively constant (8-10%). Overall, biogenic SOA accounted for approximately 75% of total SOA in summer, 50-60% in autumn and spring, and 24% in winter. Sichuan Basin had the highest predicted SOA concentrations in the country in all seasons, with hourly concentrations up to 50 µg m-3. Approximately half of the SOA in all seasons was due to the traditional equilibrium partitioning of semi-volatile components followed by oligomerization, while the remaining SOA was mainly due to reactive surface uptake of isoprene epoxide (5-14%), glyoxal (14-25%) and methylglyoxal (23-28%). Sensitivity analyses showed that formation of SOA from biogenic emissions was significantly enhanced due to anthropogenic emissions. Removing all anthropogenic emissions while keeping the biogenic emissions unchanged led to total SOA concentrations of less than 1 µg m-3, which suggests that manmade emissions facilitated biogenic SOA formation and controlling anthropogenic emissions would result in reduction of both anthropogenic and biogenic SOA.