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.