Impacts of biomass burning in peninsular Southeast Asia on the PM2.5 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.摘要：生物质燃烧（Biomass Burning, BB）通过排放细颗粒物（fine particulate matter, PM₂.₅）与臭氧（ozone, O₃）的气态前体物及一次气溶胶，对二者的生成过程产生影响。本研究采用源解析WRF-Chem模式，针对2015年3月21日至25日的一次空气污染事件开展数值模拟，评估了中南半岛生物质燃烧（BB-PSEA）对中国南方地区PM₂.₅与O₃生成的影响。该源解析模式可区分BB-PSEA与其他排放源的贡献，并能够量化BB-PSEA引发的气溶胶-辐射相互作用（aerosol-radiation interactions, ARI）与气溶胶-光解相互作用（aerosol-photolysis interactions, API）效应。与实测观测数据的对比结果表明，模式对本次空气污染事件的模拟效果良好。敏感性试验结果显示，BB-PSEA可使中国南方地区PM₂.₅浓度显著提升：云南省（Yunnan Province, YNP）区域平均浓度升高39.3 μg·m⁻³（增幅68.0%），而中国南方其他下风向区域（other downwind areas, ODA，包含贵州、广西、湖南、广东、江西、福建及浙江省）的区域平均浓度升高8.4 μg·m⁻³（增幅24.1%）。云南地区的PM₂.₅浓度升高主要源于一次气溶胶贡献，而ODA地区的PM₂.₅升高则主要来自二次气溶胶贡献。BB-PSEA使云南地区的O₃浓度提升18.1 μg·m⁻³（增幅19.4%），却使ODA地区的O₃浓度降低3.7 μg·m⁻³（降幅5.3%）。云南地区的O₃升高源于BB-PSEA的气态排放贡献，而ODA地区的O₃降低则由BB-PSEA引发的ARI与API效应所导致。此外，BB-PSEA排放的氨（NH₃）对中国南方地区二次无机气溶胶的生成具有关键促进作用，同时也是ODA地区PM₂.₅浓度升高的决定性影响因素。