Chinese Regulations Are Working—Why Is Surface Ozone Over Industrialized Areas Still High? Applying Lessons From Northeast US Air Quality Evolution

Observational data indicate increasing trends of surface ozone (O3) in China, despite emission controls that have resulted in reductions of precursor emissions. Here, we explore the cause of this contradiction, through analysis of surface observations (2014–2019) in China and historical observation record in the United States (US, 1990–2019). Our observation‐based analysis indicates that the reductions of nitrogen oxides (NOx) emissions led to increase of surface O3 in North China Plain (NCP) and Yangtze River Delta (YRD) of around 8 ppb. However, NOx controls resulted in shift of O3 chemical regimes over NCP and YRD, with turning points between NOx‐ and volatile organic compound (VOC)‐limited regimes around 2019, while model simulations suggest transitional or NOx‐limited regimes over the rest of China. The impacts of high fine particles (PM2.5) on O3 formation has declined because of the reduction of PM2.5 concentrations. Stricter NOx controls can mitigate O3 pollutions over industrialized areas in China. Plain Language Summary Ozone (O3) in surface air is an important pollutant with adverse effects on human health and vegetation growth. Here, we explore the sustainable pathway to control O3 pollution in China through analysis of observations in China (2014–2019) and the United States (US, 1990–2019). We find that the reductions of nitrogen oxides (NOx) emissions have led to increase of surface O3 in North China Plain (NCP) and Yangtze River Delta (YRD) by about 8 ppb. However, the severe O3 pollution in China can be mitigated because NOx controls led to the shift of O3 chemical regimes over NCP and YRD to transitional regime around 2019. In addition, the impacts of high fine particles (PM2.5) on O3 formation has declined because of the reduction of PM2.5 concentrations. Key Points Reductions of nitrogen oxides (NOx) led to increase of surface ozone (O3) in North China Plain and Yangtze River Delta Shift of O3 chemical regimes with turning points between NOx‐ and volatile organic compound‐limited regimes around 2019 The impacts of high fine particles (PM2.5) on O3 formation has declined with reduction of PM2.5 concentrations