Simulation of summer ozone and its sensitivity to emission changes in China

Rapid economic growth and associated emission increase in China have led to severe air pollution in recent decades. As fine particulate matter concentration is decreasing due to strict control measures, ozone (O-3) concentration has an increasing trend with adverse effects on human health and ecosystems. In this study, the Community Multi-scale Air Quality (CMAQ) model was used to investigate the formation of O-3 in China during three high concentration episodes in summer 2013 and analyzed its sensitivity to emission changes. Compared with observation data, O-3 performance met the EPA criteria of mean normalized bias (MNB) within +/- 0.15 in major parts of China including five megacities. The diurnal variation of O-3 had similar trend with temperature. The August episode (6-12) had the highest daily maximum 1-h O-3 of similar to 100 ppb in North China Plain (NCP), while the July episode (11-19) had the lowest concentrations of similar to 50 ppb. The O-3 production rates (OPR) were higher at NCP and the Yangzi River Delta (YRD), but O-3 production efficiencies (OPE) acted in contrary. O-3 isopleth showed that NOx controlled O-3 concentration in most areas of China. Reducing VOC would have minor effects on O-3 concentrations while reducing NOx could largely reduce O-3 concentration except for urban areas such as Shanghai and Guangzhou. Linear correlations were observed between secondary organic aerosol (SOA) and O-x(O-3 + NO2) concentrations in August at Shanghai and Guangzhou, indicating correlations between O-3 and other photochemical compounds. This study provides valuable information for designing effective control strategies for O-3 in China.