Regional modeling of secondary organic aerosol over China using WRF/Chem

Using a new generation air quality modeling system (WRF/Chem) fully coupled with secondary organic aerosol model (SORGAM), we investigate the spatial and temporal characteristics of secondary organic aerosol (SOA) as well as the relative contributions of anthropogenic and biogenic sources to the formation of SOA in 2006 over China. To improve SOA simulation, a parameterization scheme for the isoprene induced SOA formation was added in WRF/Chem. The simulated SOA concentrations show large temporal and spatial variability, with the highest levels occur in summer and the lowest concentrations occur in winter. The high SOA regions are located near 30°N in central China in summer, with values exceeding 8 μg m−3, while they shift to South China, mainly in Pearl River Delta (PRD) region in winter, with the concentrations at or below 2 μg m−3. Across the whole country, the average ground level SOA concentrations are 0.94, 2.54, 1.41, 0.43, and 1.34 μg m−3 in spring, summer, autumn, winter, and year, respectively. Commonly, the SOA loading is mostly concentrated in the boundary layer (∼70%). Although the SOA concentrations are dominated by biogenic sources in summer, the contributions of anthropogenic sources exceed biogenic sources over most areas in winter. On the national level, the anthropogenic sources contribute 35% of total SOA, with 41%, 26%, 39%, and 59% in spring, summer, autumn and winter, respectively. The estimated annual SOA production reaches 3.05 Tg yr−1 over China, accounting for about 4–25% of global SOA formation. The modeled OC and EC concentrations as well as SOC to OC ratios are compared with the measurements and previous studies. The results suggest that the spatial and temporal characteristic of OC and EC levels is well captured by the model. However, the simulated SOA concentrations in this study might be underestimated by 0–75%. The modeling SOA in this paper are in agreement with other field and modeling studies, also showing the importance of SOA in total organic aerosol in China.