Temporal Evolution and Correlation Analysis of PM2.5 and O₃ Concentrations in Wuhan (2016-2020)

Abstract

As a major industrial and transportation hub in central China, Wuhan has long been challenged by the compound air pollution of wintertime PM2.5 episodes and summertime O₃ pollution. This study analyzed daily air quality monitoring data from 2016 to 2020 using time-series and seasonal correlation analyses to systematically investigate the evolutionary patterns and correlation characteristics of the two pollutants. The results showed that the annual mean PM2.5 concentration decreased by 18.1%, indicating significant mitigation effectiveness, while O₃ exhibited no declining trend, remaining a persistent concern. The two pollutants displayed a clear seasonal complementarity pattern: PM2.5 peaked in winter and bottomed in summer, whereas O₃ showed the opposite pattern. At the daily scale, the overall correlation was weakly negative (r = -0.147). However, after seasonal stratification, summer exhibited a significant positive correlation (r = 0.384), winter showed a weak positive correlation, and spring/autumn correlations were not significant, revealing a classic Simpson's paradox. The findings suggest that a PM2.5-focused control strategy alone is insufficient for synergistic O₃ reduction. It is recommended to strengthen VOCs control in summer and intensify primary particle emission reductions in winter, thereby establishing a seasonally differentiated management framework to provide scientific support for precise governance of complex air pollution in central China's urban agglomerations.