汾渭平原复杂地形影响下冬季PM2.5污染分布特征、来源及成因分析

汾渭平原受其复杂地形特征及产业结构影响，和京津冀、长三角地区一起被列为大气污染重点防治区域.本研究应用2014—2019年冬季中国环境监测总站汾渭平原各城市的六大空气污染物逐小时数据，结合欧洲中心ERA-5数据，利用HYSPLIT后向轨迹模型及T-model斜交旋转主成分分析法（PCT），揭示过去6年汾渭平原冬季颗粒物浓度演变规律，厘清汾渭平原复杂地形影响下大气污染来源特征、潜在源区及成因，识别影响汾渭平原冬季空气污染的主要天气系统类型.HYSPLIT模拟结果表明，冬季喇叭口地形城市主要受本地和邻近区域污染源影响；山区盆地地形城市更易受到100~300 km距离以内污染源的传输影响，其中，来自陕北的气团对其影响最大；峡谷地形城市更易受到300~600 km范围内污染源的传输影响；平原地形城市的污染物浓度受区域传输的影响较大.影响汾渭平原冬季颗粒物重污染的天气系统可分为高压前部型、高压后部型、均压场型及低压倒槽型，其中，高压前部型是汾渭平原冬季重污染时段最易出现的天气形势.

Temporal-spatial variations, source apportionment, and formation mechanisms of PM2.5 pollution over Fenwei Plain, China

Due to complexity of terrain and industrial structures, Fenwei Plain has become one of the most polluted regions with a similar rank to Beijing-Tianjin-Hebei and the Yangtze River Delta, in China. In this study, various observational data including hourly concentrations of gaseous pollutants and particulate matter, together with the HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) model are used to characterize temporal and spatial variations in major air pollutants, identify potential sources, and understand formation mechanism of particulate matter with diameter less than 2.5 micrometers (PM_2.5) during the winters from 2014 to 2019. A T-mode with oblique rotation principal component analysis (PCT) method is used with ERA5 data to identify the synoptic weather patterns which are conducive to occurrence and aggravation of PM_2.5 pollution events in the study region. Several findings are identified from the detailed analyses. First, HYSPLIT simulations show that the cities located in Bellmouth basin are mainly affected by local and neighboring emission sources; the cities located at mountain basin are mainly affected by the emission sources from the regions with distance from 100 km to 300 km. Meanwhile, the emission sources in the range of 300~600 km exert a greater transport impact on the cities with canyon topography. The pollutant concentrations are greatly affected by regional transport in plain cities. Finally, four types of synoptic patterns are responsible for the occurrence of heavy PM_2.5 pollution events in this region. They include the front of a high-pressure system, the rear of a high-pressure system, the weather system with uniform-distribution pressure, and the system with an inverted trough.