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

Since China's clean air action, PMinline-formula_2.5 (particulate matter with an aerodynamic equivalent diameter of 2.5 inline-formulaµm or less) air quality has improved, while ozone (Oinline-formula₃) 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 Oinline-formula₃ 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 8 h average (MDA8) Oinline-formula₃ in both summer (inline-formula+1.96 ppb vs. inline-formula+0.07 ppb) and winter (inline-formula+3.56 ppb vs. inline-formula−1.08 ppb) than the impacts of changed meteorological conditions in urban areas. The decreased PMinline-formula_2.5 caused by emission reductions can result in a weaker impact of ARI on Oinline-formula₃ concentrations, which superimposes its effect on the worsened Oinline-formula₃ air quality. The weakened ARI due to decreased anthropogenic emissions aggravates the summer (winter) Oinline-formula₃ pollution by inline-formula+0.81 ppb (inline-formula+0.63 ppb), averaged over eastern China, with weakened API contributing 55.6 % (61.9 %) and ARF contributing 44.4 % (38.1 %), respectively. This superimposed effect is more significant for urban areas during summer (inline-formula+1.77 ppb). Process analysis indicates that the enhanced chemical production is the dominant process for the increased Oinline-formula₃ 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 Oinline-formula₃ air quality, indicating that more stringent coordinated air pollution control strategies should be implemented for significant improvements in future air quality.