Resolving the complex responses of ozone transport and chemistry to typhoons in South China: Insights from process-level analysis

Abstract. Typhoons are major synoptic systems linked to ozone (O₃) pollution in the Pearl River Delta, South China, particularly in autumn and summer. Although previous studies have identified various mechanisms of typhoon-induced O₃ pollution, analyses of meteorological conditions or overall process contributions alone do not fully explain how typhoons affect O₃ pollution through specific atmospheric processes, particularly transport and chemistry. Here, we combine O₃ mass budget analysis, source apportionment, precursor-transport sensitivity simulations and chemical diagnostics based on WRF-CMAQ models to investigate the responses of these processes to typhoons in autumn and summer. Typhoons enhance O₃ transport through both vertical exchange and horizontal transport, with increased transport of O₃ derived from upwind emissions in both seasons and background O₃ mainly in autumn. Transported precursors also contribute considerably to local O₃ pollution (>10 µg m^-3), which is further enhanced under typhoon influence, primarily driven by increased contributions from acyl peroxy nitrates (APNs) and NO_x. Local photochemistry exhibits more complex responses: typhoons accelerate O₃ production in autumn but suppress it in summer, reduce HO_x cycling efficiency while enhancing O₃ production efficiency, alter VOC contributions to OH reactivity, and generally shift O₃ production toward more NO_x-limited conditions. These findings reveal that typhoons influence regional O₃ pollution through multiple transport pathways, transported precursor contributions and different aspects of photochemistry, providing further process-level evidence for understanding the mechanisms underlying typhoon-induced O₃ pollution.