The Impact of Biomass Burning in Peninsular Southeast Asia on PM2.5 and Ozone Formation over Southern China in Spring

Biomass burning affects PM_2.5 and O₃ formations by emitting particles and gaseous precursors of O₃. This study aims to investigate the impact of biomass burning in peninsular Southeast Asia (PSEA) during springtime on the O₃ formation in southern China. The online coupled Weather Research and Forecasting-Chemistry (WRF-Chem) model is used to simulate a pollution episode in southern China from 21 to 25 March 2015. The model performs well in simulating the spatial and temporal distributions of PM_2.5, O₃, CO, and NO₂ concentrations during the simulation period. Biomass burning emissions in PSEA increase surface PM_2.5 concentrations by 6.2 μg m^-3 (19%) in southern China, revealing the large contribution to air pollution in southern China during springtime. The gaseous emissions from biomass burning in PSEA increase the surface MDA8 O₃ concentrations by 35 μg m^-3 (51%) in Yunnan Province nearest to PSEA and 2.5 μg m^-3 (3.2%) in the downwind areas in southern China, respectively. Considering the aerosol impact on the photolysis rates of gases, the aerosol emissions from biomass burning in PSEA decrease the photolysis rates of NO₂ and O₃(¹D), reducing the surface MDA8 O₃ concentrations by 2.1 μg m^-3 (2.3%) in Yunnan Province and 3.04 μg m^-3 (3.4%) in the downwind areas in southern China. The total effect of biomass burning in PSEA (including aerosol and gas emissions) increase the surface MDA8 O₃ concentrations by 27.9 μg m^-3 (30%) in Yunnan Province and decrease O₃ concentrations by 1.54 μg m^-3 (2%) in the downwind areas in southern China. The model results indicate that gaseous emissions from biomass burning in PSEA play a dominant role in enhancing surface O₃ concentrations in Yunnan Province nearest to the source region, while the aerosol impact on the downwind areas in southern China is larger than the gas emissions. This study highlights biomass burning in PSEA as the important source of air pollution in southern China during springtime and the complexity and nonlinearity of impact of biomass burning on O₃ photochemistry in southern China during springtime.