Decadal evolution of aerosol-mediated ozone responses in Eastern China under clean air actions and carbon neutrality policies

Despite substantial reductions in PM 2.5 and other pollutants, ozone (O 3 ) 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 insufficiently explored, particularly during Clean Air Action Plan (CAAP, 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 O 3 changes in the Yangtze River Delta (YRD), linking aerosol effects with CAAP and carbon-neutrality pathways. We separate O 3 changes into those driven directly by anthropogenic emissions and meteorological variability, and those mediated by aerosol processes through ARI and HET. The results revealed that anthropogenic emissions and meteorological variability respectively dominated winter and summer O 3 increases. Winter O 3 increases were dominated by ARI: large aerosol reductions enhanced solar radiation, temperature, and photolysis, resulting in a photochemical O 3 rise (+1.14 (+0.74) ppb in Phase I (II)). Summer O 3 was more sensitive to HET. In Phase I, aerosol decreases weakened heterogeneous radical uptake, enhancing O 3 formation (+1.62 ppb). In Phase II, however, the net HET effect reversed sign (−2.86 ppb), driven by shifts in multiple heterogeneous pathways – including changes in radical uptake, HONO and N 2 O 5 chemistry, and aerosol liquid water – rather than radical scavenging alone. Accounting for aerosol effects (AEs = ARI + HET), reductions in PM 2.5 and NO x increased O 3 , while VOCs reductions consistently lowered O 3 in both seasons. Under carbon peaking and neutrality scenarios with AEs, winter O 3 increased by 6.7 % and 10.7 %, whereas summer O 3 decreased by 2.9 % and 6.7 %, highlighting seasonally contrasting responses. These results underscore the necessity of explicitly accounting for multi-path aerosol–O 3 interactions in both near-term air quality management and long-term climate mitigation to prevent unintended trade-offs and maximize co-benefits.