Impacts of biomass burning in peninsular Southeast Asia on PM2.5 concentration and ozone formation in southern China during springtime – A case study

Abstract: Biomass burning (BB) affects fine particulate matter (PM_2.5) and ozone (O₃) formations by emitting their gaseous precursors and primary aerosols. Impacts of BB in peninsular Southeast Asia (BB-PSEA) are evaluated on the PM_2.5 and O₃ formations in southern China, using a source-oriented WRF-Chem model to simulate an air pollution episode from 21 to 25 March 2015. The source-oriented model separates the emission from the BB-PSEA and other sources and is able to evaluate the effect of aerosol-radiation interactions (ARI) and aerosol-photolysis interactions (API) from the BB-PSEA. Comparisons with observations reveal that the model performs well in simulating the air pollution episode. Sensitivity experiments show that BB-PSEA increases PM_2.5 concentrations by 39.3 μg m^-3 (68.0%) in Yunnan Province (YNP) and 8.4 μg m^-3 (24.1%) in other downwind areas (ODA) in southern China (including the provinces of Guizhou, Guangxi, Hunan, Guangdong, Jiangxi, Fujian, and Zhejiang) on the regional average. The PM_2.5 enhancement is mainly contributed by primary aerosols in YNP but by secondary aerosols in the ODA. The BB-PSEA increases O₃ concentrations of 18.1 μg m^-3(19.4%) in YNP and decreases O₃concentrations in the ODA by 3.7 μg m^-3 (5.3%). The O₃ increase in YNP is contributed by the gaseous emissions of the BB-PSEA, and the O₃ decrease in the ODA is caused by the effects of ARI and API of the BB-PSEA. The NH₃ emissions from the BB-PSEA plays a key role in enhancing secondary inorganic aerosols in southern China, and also determine the PM_2.5 increase in the ODA.