Influence of Southeast Asian biomass burning on tropospheric ozone enhancement over southern China

Biomass burning (BB) in Southeast Asia introduces natural variability, complicating ozone (O₃) control in Southern China. Using GEOS-Chem and multi-source observations from Satellite observation, O₃ sounding and ground samplers, the impacts of cross-border transport of BB on O₃ pollution and photochemical regimes were quantified. BB significantly impacts downwind megacities, modulated by the Western Pacific subtropical high (WPSH) and low-level jet (LLJ). A westward-shifted WPSH and intensified LLJ drive BB plumed into Yunnan, Pearl River Delta (PRD), and Yangtze River Delta (YRD), with O₃ enhancements up to 13.46 ppb. Vertical stratification showed peak O₃ contributions at 850-900 hPa in Yunnan and plume transport to 700 hPa over PRD and YRD. BB events shifted O₃ precursor sensitivity toward volatile organic compound-limited regimes, confirmed by decreased H₂O₂/HNO₃ ratios. These conditions necessitate dynamic emission control strategies. BB pollutants reached PRD and YRD within 4-5 days, and WPSH-LLJ configurations offered a 2-3-day lead for predictive early warnings about these cross-border BB events.