Temporal and Spatial Features of the Correlation between PM_2.5 and O₃ Concentrations in China

In recent years, particulate matter of 2.5 µm or less (PM_2.5) pollution in China has decreased but, at the same time, ozone (O₃) pollution has become increasingly serious. Due to the different research areas and research periods, the existing analyses of the correlation between PM_2.5 and O₃ have reached different conclusions. In order to clarify the relationship between PM_2.5 and O₃, this study selected mainland China as the research area, based on the PM_2.5 and O₃ concentration data of 1458 air quality monitoring stations, and analyzed the correlation between PM_2.5 and O₃ for different time scales and geographic divisions. Moreover, by combining the characteristics of the pollutants, topography, and climatic features of the study area, we attempted to discuss the causes of the spatial and temporal differences of R-PO (the correlation between PM_2.5 and O₃). The study found that: (1) R-PO tends to show a positive correlation in summer and a negative correlation in winter, (2) the correlation coefficient of PM_2.5 and O₃ is lower in the morning and higher in the afternoon, and (3) R-PO also shows significant spatial differences, including north-south differences and coastland-inland differences.