Decadal Evolution of Aerosol-Mediated Ozone Responses in Eastern China under Clean Air Actions and Carbon Neutrality Policies

Abstract. Despite substantial reductions in PM_2.5 and other pollutants, ozone (O₃) in eastern China has increased over the past decade, yet the influence of aerosol processes – including aerosol–radiation interactions (ARI) and heterogeneous chemistry (HET) – on these trends remains poorly understood, particularly during Clean Air Action (Phase I: 2013–2017; Phase II: 2018–2020) and under carbon neutrality pathways. We applied a phase- and season-resolved WRF-Chem framework with explicit ARI and HET to quantify historical and projected O₃ changes in the Yangtze River Delta (YRD), linking aerosol effects with clean air actions and carbon-neutrality pathways. Winter O₃ increases were dominated by ARI: large aerosol reductions enhanced solar radiation, temperature, and photolysis, resulting in a photochemical O₃ rise (+1.14 (+0.74) ppb in Phase I (II)). Summer O₃ was more sensitive to HET: initial aerosol decreases weakened radical scavenging, promoting O₃ formation (+1.62 ppb), whereas the weakening of this effect during Phase II reduced O₃ (-2.86 ppb). Accounting for aerosol effects (ARI+HET), reductions in PM_2.5 and NOx increased O₃, while VOCs reductions consistently lowered O₃ in both seasons. Under carbon peaking and neutrality scenarios with AEs, winter O₃ increased by 6.7 % and 10.7 %, whereas summer O₃ decreased by 2.9 % and 6.7 %, highlighting seasonally contrasting responses. These results underscore the necessity of explicitly accounting for multi-path aerosol–O₃ interactions in both near-term air quality management and long-term climate mitigation to prevent unintended trade-offs and maximize co-benefits.