Anthropogenically and meteorologically modulated summertime ozone trends and their health implications since China's clean air actions.

Elevated ozone (O) has emerged as the major air quality concern since China's clean air actions, offsetting the health benefits gained from improved air quality. Given the shifted ozone chemical regimes and recently boosted extreme weather in China, it's essential to rethink the O trends since 2013 for evaluations of air pollution mitigation policy. Here, we examine the anthropogenically and meteorologically modulated summertime O trends across China at different stages of the clean air actions using multi-source observations combined with multi-model calculations. Ozone increases steadily in China between 2013-2022, with a fast increase rate of 4.4 μg m yr in Phase I and a much smaller 0.6 μg m yr in Phase II of Action Plan. Results highlight that the deteriorative O pollution in Phase I and early Phase II is dominated by the nonlinear O-emission response. Persistent decline in O precursors has shifted its chemical regime in urban areas and began to show a positive influence on ozone mitigation in recent years. Meteorological influence on O variations is minor until 2019 (∼10%), but it greatly accelerates or relieves the O pollution after then, showing comparable contribution to emissions. Epidemiological model predicts totally 0.8-3.0 thousand yr more deaths across China with altered anthropogenic emissions since clean air actions, and additional health burdens by -1.5-0.3 thousand yr from perturbated meteorology. This study calls for stringent emission control and climate adaptation strategies to attain the ozone pollution mitigation in China.