Spatio-Temporal Characteristics of SO across Weifang from 2008 to 2020.

China has achieved good results in SO pollution control, but SO pollution still exists in some areas. Analyzing the spatio-temporal distribution of SO is critical for regional SO pollution prevention and control. Compared with existing air pollution studies that paid more attention to PM., NO and O, and focused on the macro scale, this study took the small-scale Weifang city as the research area, analyzed the temporal and spatial changes in SO, discussed the migration trajectory of SO pollution and explored the impact of wind on SO pollution. The results show that the average annual concentration of SO in Weifang has exhibited a downward trend in the past 13 years, showing the basic characteristics of "highest in winter, lowest in summer and slightly higher in spring and autumn", "highest on Sunday, lowest on Thursday and gradually decreasing from Monday to Thursday" and "highest at 9 a.m., lowest at 4 p.m. and gradually increasing from midnight to 9 a.m.". SO concentration showed obvious spatial heterogeneity: higher in the north and lower in the south. In addition, Shouguang, Changyi and Gaomi were seriously polluted. The SO pollution shifted from south to northeast. The clean wind direction (southeast wind and northeast wind) of Weifang city accounted for about 41%, and the pollution wind direction (northwest wind and west wind) accounted for about 7%. Drawing from the multi-scale analysis, vegetation, precipitation, temperature, transport situation and human activity were the most relevant factors. Limited to data collection, more quantitative research is needed to gain insight into the influence mechanism in the future.