汾渭平原吕梁市颗粒物潜在源及输送通道分析

基于汾渭平原吕梁市2017~2019年颗粒物浓度监测数据和地面气象观测数据,利用后向轨迹聚类分析法以及潜在源贡献函数(PSCF)等方法研究了吕梁市冬季PM₁₀和PM_2.5大气污染特征及其潜在源区,最后结合轨迹密度分析法(TDA)、轨迹停留时间分析法(RTA)对轨迹聚类分析得到污染输送通道进行补充分类,并分析了不同输送通道的输送特征.研究发现,吕梁市2017~2019年颗粒物年均浓度逐年下降,其中PM₁₀下降了28μg/m³,PM_2.5下降了17μg/m³,冬季下降幅度最大.3a冬季风向风速和浓度的统计分析表明吕梁市颗粒物浓度受东北和西南风影响最为显著,其原因是受当地三川河河谷地形的影响.影响吕梁市PM₁₀污染的潜在源区主要位于西南方向,PM_2.5污染的潜在源区主要分布在西南、东和东南方向,颗粒物污染输送通道可概括为:西北、西南和偏东(东+东南)通道.西北通道气流移动速度快,途经新疆、内蒙、甘肃和陕西北部等区域;西南通道气流移动速度慢,主要途经陕西中南部渭河平原等污染严重的区域;偏东通道的气流移动速度慢,气流先沿太行山东麓南下,在经过太行山的横断山谷(太行陉、井陉等)时转向进入山西.PM₁₀污染时西北通道贡献最大,偏东通道贡献最小,且两个通道下绝大多数发生的均是轻度污染,占比都在90%左右;PM_2.5污染时三类通道下发生轻度污染的比重较PM₁₀均下降,西南和偏东通道下发生中度污染以上的比重在50%左右,且西南和偏东通道途经的区域恰好是PSCF计算得到的潜在源区位置,说明了西南和偏东气流容易将细颗粒物输送至吕梁.WRF (天气预报模式)的风场模拟较为直观的解释了三类污染输送通道,且复杂地形是形成污染输送通道的一个重要因素.西北和西南污染输送通道主要受吕梁山脉的影响,偏东污染输送通道主要受太行山及其横谷的影响.

Analysis on the potential source and transmission channel of particulate matter in Lüliang City,Fenwei Plain

Based on the particulate matter concentration and surface meteorological observation data of Lüliang city in Fenwei Plain from 2017 to 2019, this paper used backward trajectory cluster analysis and potential source contribution function (PSCF) methods to study the characteristics of PM₁₀ and PM_2.5 pollution and their potential source areas in winter in Lüliang city. Combining trajectory density analysis (TDA) and trajectory dwell time analysis (RTA) to supplement the classification of polluted transmission channels obtained by trajectory clustering analysis, and analyzed the transport characteristics of different transmission channels. This study found that the annual average concentration of particulate matter in Lüliang City decreased year by year from 2017 to 2019. Among them, PM₁₀ decreased by 28μg/m³, PM_2.5 decreased by 17μg/m³, and the decline was the largest in winter. The statistical analysis of the three-year winter wind direction, wind speed and concentration showed that the concentration of particulate matter in Lüliang was most significantly affected by the northeast and southwest winds because of the local topography of the Sanchuan River valley. The potential source area of PM₁₀ pollution in Lüliang was mainly located in the southwest, and the potential source areas of PM_2.5 pollution were mainly located in the southwest, east and southeast. The particulate pollution transmission channels can be summarized as: northwest, southwest and east (east and southeast) channels. The airflow in the northwest channel moved fast, passing through Xinjiang, Inner Mongolia, Gansu, and northern Shaanxi; The airflow in the southwest channel moved slowly, mainly passing through heavily polluted areas such as the Weihe Plain in central and southern Shaanxi. The airflow in the east channel moved slowly, it first traveled south along the eastern foot of the Taihang Mountains, and turned into Shanxi when passing through the valleys(Taihangxing, Jingxing, etc.) of the Taihang Mountains. When PM₁₀ pollution occurred, the northwest channel contributed the most, and the eastern channel contributed the least, and the majority of these two channels was lightly polluted, accounting for about 90%. When PM_2.5 pollution occurred, the proportion of light pollution under the three types of channels was lower than that of PM₁₀. The proportion of moderate pollution and above under the southwest and east channels were about 50%, the areas passed by the southwest and east channels were exactly the potential source locations calculated by PSCF, which also showed that the southwest and easterly airflows were likely to transport pollutants to Lvliang. Finally, the three transportation channels were verified by the wind field simulation results of the WRF model, which shows that the transportation channel results obtained in this study are valid, and the complex terrain and variable airflow are an important factor in the transmission channel. The wind field simulation of the WRF model intuitively explains the three types of pollution transmission channels, and the complex terrain is an important factor in the formation of pollution transmission channels. The pollution transport channels in the northwest and southwest are mainly affected by the Lüliang Mountains, and the eastward pollution transport channel is mainly affected by the Taihang Mountains and its Henggu.