[Characteristics, Transport Routes, and Potential Sources of PM and O Pollution in Suzhou].

Based on the air quality and meteorological data in Suzhou from 2015 to 2022, the long-term variations in PM and O, meteorological characteristics, and their correlations were analyzed in this study. The HYSPLIT model was used to explore the main transport pathways and potential source areas of PM and O. The results showed that： ① The annual averaged concentrations of PM in Suzhou decreased steadily during the study period, and the annual average concentration from 2020 to 2022 reached the national second-level standard limit. However, the annual average concentrations of O all exceeded the national second-level standard limit. After 2017, the annual number of days that O exceeded the standard was always higher than that for PM. The number of days of compound pollution continuously decreased from nine days in 2015 to zero days in 2020, and there was no compound pollution since then. ② The most severe pollution seasons for PM and O were winter and summer, respectively. PM pollution was more likely to occur in low-temperature and high-humidity weather, while O pollution was more frequent in high-temperature and low-humidity weather. Wind direction played an important role, with northwest winds amplifying PM pollution and southeast winds boosting O. These two pollutants showed a strong correlation in summer with a coefficient reaching 0.73. ③ Cluster analysis revealed that trajectory two from Hebei Province in spring and trajectory four from Shaanxi Province in winter were prone to an increase in PM concentration. The short to medium distance trajectory 1 from Shandong Province in summer and trajectory two from Hebei Province in spring were prone to an increase in O concentration. ④ The analysis of potential source areas showed that transportation outside the province had a significant impact on PM and O pollution in Suzhou. The potential source areas of PM in spring and winter were mainly distributed in Anhui Province, Henan Province, and Hubei Province； the potential source areas in autumn were mainly distributed in Hubei Province and Jiangxi Province； and the potential source areas of O in spring and summer were mainly located in the Beijing-Tianjin-Hebei Region, Shandong Province, Henan Province, and Shanxi Province. Valuable management insights for the coordinated control of PM and O pollution in Suzhou were put forward based on this study.