[Characteristics and Influencing Factors of PM_2.5-O₃ Double High Combined Pollution in Baoding City]

PM_2.5 and O₃ pollution are the main problems restricting the improvement of air quality in Baoding City. Based on the pollutant concentration and meteorological data of Baoding City from 2017 to 2022, random forest, backward trajectory cluster analysis, and the WRF-CAMx model were used to study the spatiotemporal changes, influencing factors, and pollution sources of PM_2.5 and O₃ pollution. The results showed that the overall PM_2.5 mass concentration in Baoding City decreased year by year from 2017 to 2022, and the O₃ concentration fluctuated. After the epidemic ended in 2022, air pollution rebounded. PM_2.5 pollution was concentrated in winter, O₃ pollution was highest in summer, and PM_2.5-O₃ composite pollution mainly occurred in spring. Relative humidity, CO, and NO₂ were the main factors affecting PM_2.5 mass concentration in Baoding City, while solar radiation, temperature, and NO₂ had a significant impact on O₃ concentration. PM_2.5 pollution mostly occurred under low temperature, high humidity, and low wind speed conditions, while O₃ pollution was more obvious under conditions of high temperature, strong solar radiation, and moderate humidity. Analysis of pollution sources showed that PM_2.5-O₃ composite pollution was dominated by local emissions, while external inputs mainly came from central and southern Hebei and northern Henan, especially the areas surrounding Baoding City, which contributed significantly. Therefore, it is necessary to implement staged and differentiated treatment according to the pollution characteristics of different seasons, strengthen the coordinated control of PM_2.5 and O₃, focus on the pollution effects under specific meteorological conditions, and strengthen pollution prediction and early warning. At the same time, air quality should be systematically improved through local pollution control and regional joint prevention and control.