Weakened aerosol-radiation interaction exacerbating ozone pollution in eastern China since China's clean air actions

Since China's clean air action, PM2.5 (particulate matter with an aerodynamic equivalent diameter of 2.5gm or less) air quality has improved, while ozone (O3) pollution has become more severe. Here we apply a coupled meteorology-chemistry model (WRF-Chem: Weather Research and Forecasting model coupled to Chemistry v3.7.1) to quantify the responses of aerosol-radiation interaction (ARI) to anthropogenic emission reductions from 2013 to 2017, including aerosol-photolysis interaction (API) related to photolysis rate change and aerosol-radiation feedback (ARF) related to meteorological field change and their contributions to O3 increases over eastern China in summer and winter. Sensitivity experiments show that the decreased anthropogenic emissions play a more prominent role in the increased daily maximum 8gh average (MDA8) O3 in both summer (+1.96gppb vs. +0.07gppb) and winter (+3.56gppb vs.-1.08gppb) than the impacts of changed meteorological conditions in urban areas. The decreased PM2.5 caused by emission reductions can result in a weaker impact of ARI on O3 concentrations, which superimposes its effect on the worsened O3 air quality. The weakened ARI due to decreased anthropogenic emissions aggravates the summer (winter) O3 pollution by +0.81gppb (+0.63gppb), averaged over eastern China, with weakened API contributing 55.6g% (61.9g%) and ARF contributing 44.4g% (38.1g%), respectively. This superimposed effect is more significant for urban areas during summer (+1.77gppb). Process analysis indicates that the enhanced chemical production is the dominant process for the increased O3 concentrations caused by weakened ARI in both summer and winter. This study innovatively reveals the adverse effect of weakened aerosol-radiation interaction due to decreased anthropogenic emissions on O3 air quality, indicating that more stringent coordinated air pollution control strategies should be implemented for significant improvements in future air quality.