Coordinated control of PM and O is urgently needed in China after implementation of the "Air pollution prevention and control action plan".

To improve air quality, China formulated the Air Pollution Prevention and Control Action Plan (APPCAP) in 2013. In the present study, the changes in the concentration of air pollutants after the implementation of APPCAP were investigated based on nationwide monitoring data. From the results, it is evident that the annual mean concentrations of PM, PM, SO, and CO show a significant downward trend over 2015-2018, with decreasing rates of 3.4, 4.1, 3.8, and 70 μg m/year, respectively. However, no significant change was found in NO while maximum daily 8 h average O concentration (MDA8 O) was increased by 3.4 μg m/year during the four years. Spatially, the highest decrease in PM was found in Beijing-Tianjin-Hebei (BTH), followed by central China and northeast China, while the Pearl River Delta (PRD), Yungui Plateau, and northwest China showed less decreases. MDA8 O had a higher increase in BTH, central China, Yangtze River Delta (YRD), and PRD. With the decrease in PM in recent years, cumulative population exposure to PM gradually decreased, whereas there was still more than 65% of the population exposing to annual PM higher than the standard of 35 μg m in 2018. In contrast, the health effects of O gradually increased with 13.1%, 14.3%, 20.4%, and 21.7% of the population exposed to unhealthy O levels in summer from 2015 to 2018. O pollution is causing severe health risks with estimated nationwide mortality of 70,024 (95% CI: 55,510-84,501), 79,159 (95% CI: 62,750-95,525), 105,150 (95% CI: 83,378-126,852), and 104,404 (95% CI: 82,784-125,956) in the four years, respectively. This clearly shows that the target of air pollution control in China shifts and coordinated control of PM and O is urgently needed after the successful implementation of APPCAP.