The implementation of the "Three-Year Action Plan for Winning the Blue Sky Defense Battle" has significantly reduced surface ozone pollution and its impacts on crop yields in China.

China has experienced a substantial reduction in PM2.5 concentrations since the enforcement of the "Air Pollution Prevention and Control Action Plan (APPCAP)". However, surafce ozone (O3) levels and the resulting threats to agriculture have intensified. To further mitigate PM2.5 pollution, the government promulgated the "Three-Year (2018-2020) Action Plan for Winning the Blue Sky Defense Battle" (the Blue Sky Defense Battle). Throughout its implementation, research has consistently shown a steady decrease in PM2.5 levels. Yet, it is still uncertain whether this reduction in PM2.5 would lead to a rise in O3 pollution and its associated effects on agriculture, similar to the patterns observed during the APPCAP period. This study utilized nationwide O3 monitoring data to systematically evaluate O3 concentrations and agricultural risks during the Blue Sky Defense Battle period. Results indicated that from 2018 to 2020, the maximum daily 8-h running average O3 concentration (MDA8 O3) in China decreased by 3.8 %. Spatially, regions such as Beijing-Tianjin-Hebei, the Yangtze River Delta, and the Fen-Wei Plain exhibited notably high MDA8 O3 concentrations. By 2020, the Accumulated O3 exposure over a Threshold of 40 ppb (AOT40) values had declined by 16.2 % and 8.1 % in regions cultivating winter wheat and single rice, respectively, compared to 2018. During 2018-2020, the average relative yield losses due to O3 were 22.1-27.2 % for winter wheat and 7.5-9.2 % for single rice. Additionally, in 2020, O3-related crop production losses (CPL) reached 6.35 × 107 tons for winter wheat and 1.07 × 107 tons for single rice, representing reductions of 21.0 % and 12.3 %, respectively, compared to 2018. Spatially, higher CPL of winter wheat were mainly observed in Henan, Hebei, and Shandong, while higher CPL of single rice were distributed in Jiangsu, Hubei, and Anhui. In summary, this study revealed the effectiveness of the Blue Sky Defense Battle in mitigating O3 pollution and emphasized the necessity of regional O3 control targeting major crop production areas to reduce agricultural risks.