Pollution characteristics, potential source areas, and transport pathways of PM2.5 and O3 in an inland city of Shijiazhuang, China

Regional transmission plays a crucial role in the PM_2.5 and O₃ pollution of Shijiazhuang, a hot inland city in the North China Plain. To analyze the pollution pathways and potential source distribution, airflow backward trajectory cluster analysis, potential source contribution function (PSCF) method, and concentration-weighted trajectory (CWT) analysis were used adopting monitoring data from 2015 to 2021. The results showed that in 2016, the compound pollution days of PM_2.5 and O₃ were the most (24 days), accounting for 36.4% of the total. According to air mass backward trajectory analysis, the highest concentration of O₃ in Shijiazhuang during summer (136.3 μg/m³) was due to the influence of short-distance transmission, specifically Cluster 3 from the southeast direction accounting for the most significant proportion (32.79%). In winter, PM_2.5 pollution primarily originated from long-distance transmission, with Cluster 3 in Mongolia, Inner Mongolia, and Shanxi Province recording PM_2.5 concentrations as high as 179.9 μg/m³. The source area for PM_2.5 pollution in Shijiazhuang significantly expanded during winter, with the increasing high-value area of weighted PSCF (WPSCF) and weighted (WCWT). During summer, the distribution area of O₃ pollution sources and WPSCF value increased significantly. Almost the entire Henan region was covered by a high-value WCWT area (up to 95 μg/m³). O₃ pollution was primarily emitted locally but transported over short distances. These findings underscore the necessity of implementing regional joint prevention and control measures to mitigate PM_2.5 and O₃ pollution.

Graphical Abstract