Abstract: The Yangtze River Delta urban agglomeration is a densely populated region with a highly developed economy and advanced technology. However, the high energy consumption in this region has led to significant environmental challenges. Spatiotemporal distribution of PM_2.5 concentration and its evolution trend were analyzed with the air quality data of 202 stations in the near surface layer from January 2015 to May 2022. The transport routes and potential contributing areas of the pollutants were determined with the help of the Hysplit model. Based on the modelling results, the effects of wind and topographic changes on pollutant enrichment and diffusion were discussed. The results showed that: (1)The average concentration of PM_2.5 in the Yangtze River Delta urban agglomeration was 38.26 μg/m3, which was slightly higher than the air quality standard in China. However, among the studied 202 stations, the number of sites with annual average values exceeding the standard accounted for 26.24%, and the number of sites with daily average values exceeding the standard accounted for as high as 92.08%, mainly occurred in winter. This implied that the air quality in this region still faced severe challenges; (2)Under the background of economic development with ecological priority, the annual average concentration of PM2.5 in the region showed a significant downward trend at a rate of 4.07 μg/(m3·a), for the studied period. The decrease was the most significant around the center of Hefei-Chuzhou and the line of Yangzhou-Taizhou-Wuxi-Suzhou-Yuhang (Hangzhou), which indirectly indicated the policy strength in action in the main body of the Yangtze River Delta, in an attempt to deal with the environmental pollution. (3)The correlation of PM2.5 concentration with the wind speed was worthy of attention in the Yangtze River Delta urban agglomeration. When the wind speed was greater than 4 m/s, more pollutants could be transported into the study area, worsening air quality. The proportion of days with PM2.5 concentration failing to meet the standard (Level 1 standard) increased with the increase of wind speed. (4)In winter, the strong northerly winds transported pollutants mainly originated from human emissions in the area around the Yellow Sea and along the lines of Handan-Jining-Zaozhuang-Southwest Huaian-Chuzhou, and consequently affected the PM2.5 concentration. Therefore, it was suggested that the Yangtze River Delta urban agglomeration carry out cross-regional ecological compensation, relying on economic and technological advantages to limit or reduce the discharge of pollutants from external sources, and to improve the livability of the Yangtze River Delta urban agglomeration.