Anthropogenic drivers of 2013–2017 trends in summer surface ozone in China

Significance Drastic air pollution control in China since 2013 has achieved sharp decreases in fine particulate matter (PM 2.5 ), but ozone pollution has not improved. After removing the effect of meteorological variability, we find that surface ozone has increased in megacity clusters of China, notably Beijing and Shanghai. The increasing trend cannot be simply explained by changes in anthropogenic precursor [NO x and volatile organic compound (VOC)] emissions, particularly in North China Plain (NCP). The most important cause of the increasing ozone in NCP appears to be the decrease in PM 2.5 , slowing down the sink of hydroperoxy radicals and thus speeding up ozone production. Decreasing ozone in the future will require a combination of NO x and VOC emission controls to overcome the effect of decreasing PM 2.5 .