川南自贡市大气颗粒物污染特征及传输路径与潜在源分析

Analysis of Transport Pathways and Potential Sources of Atmospheric Particulate Matter in Zigong,in South of Sichuan Province

川南自贡市大气颗粒物污染比较严重, 2015~2018年PM10和PM2.5平均浓度分别为(95.42±9.53)μg·m-3和(65.95±6.98)μg·m-3,并有明显的下降趋势,冬季PM10和PM2.5浓度远高于其它季节, 1月平均浓度最高,分别为(138.08±52.29)μg·m-3和(108.50±18.05)μg·m-3,夏季平均浓度最低.PM2.5与PM10的平均比值为69.12%,冬季比值约为夏季的1.17倍,空气污染以PM2.5为主.采用拉格朗日混合单粒子轨迹模型(HYSPLIT)和全球资料同化系统的GDAS气象数据,对自贡市细颗粒物(PM2.5)浓度和逐日72 h后向轨迹进行计算和聚类研究,利用潜在源贡献分析法(PSCF)和浓度权重轨迹分析法(CWT),探讨不同季节影响自贡市PM2.5浓度的潜在源区以及不同源区的污染贡献.结果表明,自贡市近地面四季多受东南风、偏西风和西北风控制,高浓度PM2.5多出现在0~2 m·s-1的低风速区;不同季节、不同输送路径对自贡PM2.5污染影响的差异显著,春季主要受到来自偏西和偏北方向短距离输送气流的影响,夏季污染轨迹主要来自短距离输送的东南气流,秋季主要受来自资阳,经遂宁、重庆和内江的短距离输送气流的影响,冬季除受到资阳、遂宁和内江等周边城市的影响外,还受到来自西藏中部的远距离输送气流影响;除夏季外,自贡市潜在源区主要位于重庆西部与川南交界区域,冬季的主要贡献区范围最广、贡献程度最大,夏季潜在源区范围最小且贡献程度最弱.

Atmospheric particulate matter pollution in Zigong City in southern Sichuan is quite severe.The average concentrations of PM10 and PM2.5 from 2015 to 2018 were(95.42±9.53)μg·m-3 and(65.95±6.98)μg·m-3,with an obvious trend of decline.The concentrations of PM10 and PM2.5 in winter were much higher than in other seasons,with the highest average concentrations being(138.08±52.29)μg·m-3 and(108.50±18.05)μg·m-3 in January,respectively,whereas in summer,the average concentrations were lowest.The average ratio of PM2.5 to PM10 is 69.12%,and the ratio in winter is about 1.17 times that in summer;thus,PM2.5 is mainly responsible for the air pollution.To explore the potential sources of fine particulate matter(PM2.5)in Zigong City and the pollution contributions of different sources in different seasons,the concentration of PM2.5 in Zigong and the daily trajectory after 72 h were calculated and clustered by the combined use of a variety of potential source analysis methods and data.These methods and data included the hybrid single particle lagrangian integrated trajectory(HYSPLIT)model,global data assimilation system(GDAS)meteorological data,potential source contribution analysis(PSCF),and concentration of weight trajectory analysis(CWT).The results showed that the area near Zigong is mostly controlled by southeasterly,westerly,and northwesterly winds in all seasons,and the high PM2.5 concentration is mostly located in the low-wind-speed zone of 0-2 m·s-1.The influence of different seasons and transport routes on PM2.5 pollution in Zigong is significant.In spring,it is mainly affected by short-distance air flow from the west and north;in summer,the pollution mainly comes from the southeast air flow of short-distance transportation;in autumn,it is mainly affected by short-distance transportation air flow from Ziyang,Suining,Chongqing,and Neijiang;and in winter,it is not only affected by the surrounding cities such as Ziyang,Suining,and Neijiang but also by the long-distance transportation air flow from central Tibet.In general,the potential source area of particulate matter in Zigong City is mainly located in the border area between the west of Chongqing and the south of Sichuan.In winter,the main contribution area is at its widest,while in summer,the potential source area is smallest.