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

Abstract. Despite substantial reductions in PM2.5 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 PM2.5 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.