Urban Surface Ozone Concentration in Mainland China during 2015–2020: Spatial Clustering and Temporal Dynamics

Urban ozone (O 3 ) pollution in the atmosphere has become increasingly prominent on a national scale in mainland China, although the atmospheric particulate matter pollution has been significantly reduced in recent years. The clustering and dynamic variation characteristics of the O 3 concentrations in cities across the country, however, have not been accurately explored at relevant spatiotemporal scales. In this study, a standard deviational ellipse analysis and multiscale geographically weighted regression models were applied to explore the migration process and influencing factors of O 3 pollution based on measured data from urban monitoring sites in mainland China. The results suggested that the urban O 3 concentration in mainland China reached its peak in 2018, and the annual O 3 concentration reached 157 ± 27 μg/m 3 from 2015 to 2020. On the scale of the whole Chinese mainland, the distribution of O 3 exhibited spatial dependence and aggregation. On the regional scale, the areas of high O 3 concentrations were mainly concentrated in Beijing-Tianjin-Hebei, Shandong, Jiangsu, Henan, and other regions. In addition, the standard deviation ellipse of the urban O 3 concentration covered the entire eastern part of mainland China. Overall, the geographic center of ozone pollution has a tendency to move to the south with the time variation. The interaction between sunshine hours and other factors (precipitation, NO 2 , DEM, SO 2 , PM 2.5 ) significantly affected the variation of urban O 3 concentration. In Southwest China, Northwest China, and Central China, the suppression effect of vegetation on local O 3 was more obvious than that in other regions. Therefore, this study clarified for the first time the migration path of the gravity center of the urban O 3 pollution and identified the key areas for the prevention and control of O 3 pollution in mainland China.