境外生物质燃烧对滇西地区春季大气细颗粒物含量的影响分析

Impact of Overseas Biomass Combustion on Atmospheric Fine Particulate Matter Content in Spring in Western Yunnan

利用2019年3月至2022年2月地面空气质量数据、气象观测数据和MODIS卫星热源点数据,结合TrajStat模式和区域大气化学模式WRF-Chem,对滇西地区大气污染传输特征及境外生物质燃烧影响进行定量分析。结果表明,滇西地区冬春季空气质量较差,其中,春季最差,此时各类污染物浓度均最高,首要污染物以细颗粒物(PM2.5)为主,MODIS卫星热源点监测显示,春季境外热源点密度增多,在偏西气流引导下影响滇西地区,且春季污染时段内偏西气流轨迹占比最高,超过80%,经印度北部、孟加拉国、缅甸中北部的中长距离偏西输送轨迹携带的PM2.5浓度最高;使用潜在源贡献因子(Potential Source Contribution Function,PSCF)和浓度权重轨迹(Concentration-Weighted Trajectory,CWT)方法分析发现,春季污染时段内主要贡献源区集中在德宏以西的缅甸中北部、印度东北部以及孟加拉国东部地区,浓度贡献水平为70~120μg/m3,权重潜在源贡献因子(Weighted PSCF,WPSCF)和加权浓度权重轨迹(Weighted CWT,WCWT)高值区与热源点密集区基本吻合或位于其下风风向;运用WRF-Chem模式对滇西地区一次污染过程的地面PM2.5浓度进行模拟,结果表明,生物质燃烧是滇西地区大气PM2.5的最主要来源,在模拟的污染时段贡献占比约71%。

Air pollution transmission and the impact of international biomass combustion on western Yunnan between March 2019 and February 2022 was investigated.The analysis is based on ground air quality measurements,meteorological observations,and MODIS satellite heat source points,using the TrajStat model and the regional atmospheric chemistry model WRF-Chem.The findings indicate that air quality in western Yunnan significantly deteriorates in winter and spring,with spring being the worst season due to high concentrations of pollutants,particularly particulate matter(PM2.5).MODIS data reveal an increase in overseas heat source points in spring,which,driven by westerly winds,significantly impacts western Yunnan.During the spring pollution period,over 80%of the pollution is associated with westerly wind trajectories originating from northern India,Bangladesh,and central and northern Myanmar,which carry the highest PM2.5 concentrations.Analysis using the Potential Source Contribution Function(PSCF)and Concentration-Weighted Trajectory(CWT)methods revealed that the main pollution source areas were concentrated in central and northern Myanmar to the west of Dehong,China,Northeast India,and eastern Bangladesh during the spring pollution period,with pollutant concentration contribution levels ranging from 70μg/m3 to 120μg/m3.These high-value areas of the Weighted PSCF(WPSCF)and the Weighted CWT(WCWT)accord with or are located downwind of heat-concentration zones.Simulations using the WRF-Chem model show that during a pollution event in western Yunnan,biomass combustion is the main source of PM2.5,accounting for about 71%of the simulated pollution period.