Quantifying ecological and health risks of ground-level O across China during the implementation of the "Three-year Action Plan for Cleaner Air".

After China implemented the Air Pollution Prevention and Control Action Plan (APPCAP), PM concentrations decreased but were still higher than national standards in major areas and ozone (O) concentration increased unintentionally. To further decrease PM concentrations and reduce days with severe air pollution, the government promulgated the "Three-year (2018-2020) Action Plan for Cleaner Air" (the Three-year Action Plan) in 2018. During the three-year Action Plan, a few studies reported a continuous decline in PM, but it is unclear whether O and its effects also increase with the decrease of PM like during APPCAP. In this study, for the first time, we systematically assessed changes in ground-level O concentrations and related ecological and health risks during the period of the Three-year Action Plan using nationwide O measurements. The national MDA8, Exceedance, and SOMO35 indicators were reduced by 3.8%, 28.5%, and 12.6%, respectively, ecological risk indicators of M12, M7, SUM06, AOT40, and W126 were reduced by 5.4%, 5.6%, 19.5%, 15.4%, and 18.6%, respectively, from 2018 to 2020. Spatially, the greatest reduction in all the indicators except MDA8 occurred in Pearl River Delta, followed by Fen Wei Plains, while Beijing-Tianjin-Hebei, Chengdu-Chongqing, and Yangtze River Delta presented relatively small reductions. Between 2018 and 2020, the production losses caused by O for wheat and rice decreased by 21.4% and 17.6%, respectively. Long-term exposure to O across China over 2020 was estimated to cause about 160,795 (95% CI: 81,515-312,983) for all-cause mortality, 107,128 (95% CI: 36,703-173,823) for cardiovascular mortality, and 34,444 (95% CI: 0-72,609) for respiratory mortality, indicating decreases of 9.93%, 9.86%, and 9.78%, respectively, compared to the year 2018. Taken together, our results provided the first direct evidence for China's efforts to control O pollution in recent years.