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

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 NOx. Local photochemistry exhibits more complex responses: typhoons accelerate O3 production in autumn but suppress it in summer, reduce HOx cycling efficiency while enhancing O3 production efficiency, alter VOC contributions to OH reactivity, and generally shift O3 production toward more NOx-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.