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.