[Characteristics, Transport Routes, and Potential Sources of PM_2.5 and O₃ Pollution in Suzhou]

Based on the air quality and meteorological data in Suzhou from 2015 to 2022, the long-term variations in PM_2.5 and O₃, 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_2.5 and O₃. The results showed that： ① The annual averaged concentrations of PM_2.5 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 O₃ all exceeded the national second-level standard limit. After 2017, the annual number of days that O₃ exceeded the standard was always higher than that for PM_2.5. 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_2.5 and O₃ were winter and summer, respectively. PM_2.5 pollution was more likely to occur in low-temperature and high-humidity weather, while O₃ pollution was more frequent in high-temperature and low-humidity weather. Wind direction played an important role, with northwest winds amplifying PM_2.5 pollution and southeast winds boosting O₃. 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_2.5 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 O₃ concentration. ④ The analysis of potential source areas showed that transportation outside the province had a significant impact on PM_2.5 and O₃ pollution in Suzhou. The potential source areas of PM_2.5 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 O₃ 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_2.5 and O₃ pollution in Suzhou were put forward based on this study.