The study examines the factors driving summertime surface ozone trends in China from 2013 to 2017, focusing on the period from June to August (JJA). Observations from over 1,000 sites across China show severe summertime ozone pollution and regionally variable trends. By using a multiple linear regression model, the authors isolate the effect of meteorological variability on ozone trends, revealing increasing ozone trends of 1–3 ppbv a−1 in megacity clusters of eastern China, attributed to changes in anthropogenic emissions. Specifically, anthropogenic NOx emissions decreased by 21% during this period, while volatile organic compounds (VOCs) emissions changed little. The decrease in NOx emissions would increase ozone under VOC-limited conditions in urban areas but decrease ozone under NOx-limited conditions in rural areas. However, simulations with the Goddard Earth Observing System Chemical Transport Model (GEOS-Chem) indicate that the most significant factor for ozone trends in the North China Plain is the 40% decrease in fine particulate matter (PM2.5) over the same period, which slows down the sink of hydroperoxy radicals and thus stimulates ozone production. The authors conclude that reducing ozone in the future will require a combination of NOx and VOC emission controls to counteract the effects of decreasing PM2.5 levels.The study examines the factors driving summertime surface ozone trends in China from 2013 to 2017, focusing on the period from June to August (JJA). Observations from over 1,000 sites across China show severe summertime ozone pollution and regionally variable trends. By using a multiple linear regression model, the authors isolate the effect of meteorological variability on ozone trends, revealing increasing ozone trends of 1–3 ppbv a−1 in megacity clusters of eastern China, attributed to changes in anthropogenic emissions. Specifically, anthropogenic NOx emissions decreased by 21% during this period, while volatile organic compounds (VOCs) emissions changed little. The decrease in NOx emissions would increase ozone under VOC-limited conditions in urban areas but decrease ozone under NOx-limited conditions in rural areas. However, simulations with the Goddard Earth Observing System Chemical Transport Model (GEOS-Chem) indicate that the most significant factor for ozone trends in the North China Plain is the 40% decrease in fine particulate matter (PM2.5) over the same period, which slows down the sink of hydroperoxy radicals and thus stimulates ozone production. The authors conclude that reducing ozone in the future will require a combination of NOx and VOC emission controls to counteract the effects of decreasing PM2.5 levels.