Urban ozone (O₃) 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 O₃ 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 O₃ pollution based on measured data from urban monitoring sites in mainland China. The results suggested that the urban O₃ concentration in mainland China reached its peak in 2018, and the annual O₃ concentration reached 157 ± 27 μg/m³ from 2015 to 2020. On the scale of the whole Chinese mainland, the distribution of O₃ exhibited spatial dependence and aggregation. On the regional scale, the areas of high O₃ concentrations were mainly concentrated in Beijing-Tianjin-Hebei, Shandong, Jiangsu, Henan, and other regions. In addition, the standard deviation ellipse of the urban O₃ 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, NO₂, DEM, SO₂, PM_2.5) significantly affected the variation of urban O₃ concentration. In Southwest China, Northwest China, and Central China, the suppression effect of vegetation on local O₃ 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 O₃ pollution and identified the key areas for the prevention and control of O₃ pollution in mainland China.

Sulfamerazine (SMR) as a persistent organic pollutant in waste streams is of growing environmental concern. This study explores the extraction SMR from water into an acetic acid (AA) solution using granular activated carbon (GAC), and removal of SMR by ozonation in AA solution. Systematic experiments have shown that GAC can be used as an adsorbent to transfer sulfamerazine from water to AA solution. SMR removal efficiency is 99.5% in 10% AA aqueous solution, which is better than in water. The removal rate of SMR in the AA solution decreased as the initial molar ratio of SMR and O₃ increased. The removal rate of SMR decreased with Fe³⁺ present in the reactive system. The removal of SMR is dominated by indirect ozonation in water, while the SMR removal is an effect of both direct and indirect ozonation in AA solution. It is a very efficient process for the degradation of SMR in micro polluted water when using combined GAC adsorption–desorption in AA solution and ozonation of the resulting solution.