太原市秋冬季大气污染特征和输送路径及潜在源区分析

采用环境空气质量指数(AQI)统计分析了2014～2018年太原市全年及秋冬季污染特征,并采用HYSPLIT后向轨迹模型计算了2014～2017年秋冬季逐时后向轨迹,结合太原市AQI,通过聚类分析、潜在源贡献因子和浓度权重轨迹方法对影响太原市的污染物输送路径和潜在源区进行了分析.结果表明,太原市污染状况不容乐观,太原市2014～2018年全年优良天数波动较大,尤其近两年从64%下降到不足50%;然而秋冬季优良天数稳步上升,2018年超过50%,空气质量有好转趋势.污染类型可能发生变化,全年及秋冬季PM_(2.5)为首要污染物的污染天数下降显著,PM_(10)为首要污染物的天数上升明显.聚类分析2014～2017年秋冬季太原的后向轨迹,53%的气团来自偏西方向,21%来自西北方向,12%来自西南方向,14%来自偏东方向,其中西南方向轨迹是外来污染物输送进入太原的主要轨迹,对太原空气质量有显著影响.PSCF和CWT分析表明,影响太原空气质量的重要潜在源区主要位于汾渭平原的陕西汉中、西安和山西的吕梁、临汾等地.建立汾渭平原及其周边区域联防联控机制对控制区域污染有着重要意义.

Characteristics, Transportation, Pathways, and Potential Sources of Air Pollution During Autumn and Winter in Taiyuan

Because of the atmospheric regional transmission, the air quality in Taiyuan is susceptible to air pollution from the surrounding areas. The annual and seasons air pollution characteristics of Taiyuan from 2014 to 2018 were analyzed using the environmental air quality index (AQI), the hourly backward trajectories in autumn and winter of 2014-2017 were calculated using the HYSPLIT model. The results showed that the air pollution situation in Taiyuan is not optimistic. There was a large fluctuation in the number of good days from 2014 to 2018, especially in the compliance rate of air quality, which varied from 64% to less than 50% over the past two years. However, the proportion of good days gradually increased in autumn and winter, exceeding 50% in 2018, and the trend in air quality improvement was obvious. The results also showed that air pollution may be more serious in spring and summer. Pollution types changed; whether annual or autumn and winter the days, PM_2.5 as the main pollutant decreased significantly and the days with PM₁₀ increased significantly in autumn and winter. Based on the backward trajectory model and it combination with the AQI, using Taiyuan as the starting point, the backward 72 hour trajectory from 00:00 on September 1, 2014 to 23:00 on December 31,2017 was calculated. The trajectory clustering analysis method, the potential source contribution factor weights (PSCF), and the concentration of the trajectory analysis (CWT) were used to discuss the source of contaminants in Taiyuan. The results showed that the simulated track after a clustering analysis could be divided into 8 categories, 53% of the trajectories come from the western region, 21% from the northwest, 12% from the southwest, and 14% from the east in autumn and winter of 2014-2017. The southwest trajectory was the main trajectory for the transportation of foreign pollutants into Taiyuan, and it has a significant impact on Taiyuan''s air quality. PSCF and CWT analysis showed that the major potential sources affecting Taiyuan''s air quality were mainly located in Fenwei plain, i. e., Hanzhong, Xi''an in Shaanxi Province, and Lvliang and Linfen in Shanxi Province. Establishing a joint prevention and control mechanism in the Fenwei plain and its surrounding areas would be of great significance for controlling pollution in the area.