Simulation of photochemical pollutants in summer 2013 in China

Rapid economic growth and associated emissions increase in China have led to severe air pollution in recent decades. Photochemical pollutants are secondary formed pollutants in the atmosphere with the existence of sunlight. Ozone (O3) is adverse to human health and ecosystems and secondary organic aerosol (SOA) is a major component of fine particulate matter (PM2.5) that affects human health, visibility, and climate. In this work, the Community Multi-scale Air Quality (CMAQ) model was used to investigate the formation of O3 and SOA in three episodes from June to August 2013. Compared with observation data, O3 performance meets the EPA criteria of mean normalized bias (MNB) within ± 0.15 in major parts of China including five megacities. The diurnal variation of O3 had similar trend with the temperature. The August episode has the highest O3 concentrations of 100 ppb in North China Plain while the July episode has the lowest concentrations of 50 ppb. SOA concentrations were up to 35-40 μgm-3 at different cities in different episodes. Biogenic SOA was the majority with the contributions from glyoxal (GLY), methylglyoxal (MGLY), isoprene epoxydiol (IEPOX) and oligomers (OLGM) of 70%. Isopleth found that NOx controls O3 concentration in most areas of China. Reducing VOC would have minor effects on O3 concentrations while reducing NOx could largely reduce O3 concentration except for urban areas such as Shanghai and Guangzhou. On the contrary, SOA was controlled by VOCs in cities such as Beijing, Shanghai, and Xi'an. This study provides valuable information for designing effective control strategies for O3 and particulate matter in China.