RESUMEN
In this study, the 24-hour backward trajectories of air mass at ground level(10 m)in Nanjing were calculated by using the HYSPLIT model with the NCEP global reanalysis data from April 1st to October 31st, 2017. The backward trajectories were then combined with the hourly concentration data of O3 in Nanjing for trajectories clustering analysis and potential pollution sources analysis. The results show that in 2017, the maximum daily 8 h running average O3 level in Nanjing was around 12-261 µg·m-3 with 58 days of O3 pollution in Nanjing, mainly in the spring and summer. The monthly variation of O3 showed a single peak, with the highest O3 concentration, as well as the most days exceeding the standard, occurring in June; the diurnal variation of O3 was unimodal and reached its peak around 14:00. A total number of 5136 trajectories were obtained by simulation, among which the exceeded trajectories accounted for approximately 10%. The exceedance trajectories in May and June were significantly higher, accounting for 60% of the total exceedance trajectories. Six ground-level air mass transporting pathways were identified through clustering analysis, from the NNE, NW, SW, SSE, SE, and NE directions. The SE and SSE directions with higher O3 levels were the dominant transport routes of O3 pollution, contributing to 23.33% and 20.76% of backward trajectories, respectively. As for the potential pollution source analysis, the area with high WCWT value distribution matched the WPSCF result, indicating that the potential sources of O3 pollution were mainly distributed in Changzhou, Wuxi, Suzhou, Huzhou, and other cities around Taihu Lake. Additionally, cities located around Nanjing, such as Taizhou, Ma'anshan, Wuhu, Chuzhou, Nantong, and Lianyungang, were considered the secondary potential sources. The results indicate that O3 pollution in Nanjing is a regional issue and its control requires joint prevention and control strategies in the Yangtze River Delta.