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

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.