Unraveling Spatiotemporal Synergistic Features of PM2.5–O3 and Systematic Management Policy Based on Multiple Scenario-Driven Factor Analysis in the Changsha–Zhuzhou–Xiangtan Urban Agglomeration, Central China

Fine particulate matter (PM2.5) and ozone (O3) are the key factors restricting the continuous improvement of air quality in the Changsha–Zhuzhou–Xiangtan urban agglomeration (CZT). Due to the potential correlation between variations in urban PM2.5–O3 concentration, the analysis of its composite pollution characteristics is helpful in formulating accurate and thorough air control policies. Based on the long-term concentration change in PM2.5 and O3, this study analyzed the features and synergistic factors of PM2.5–O3 pollution in the CZT by using spatial autocorrelation and a linear driving model of PM2.5–O3. The results showed that from 2017 to 2023, under the current Chinese atmospheric environment standard, the CZT saw four combined pollution days. However, if the daily limit values were viewed in line with Grade II of the WHO transition period (O3: 120 μg/m3, PM2.5: 50 μg/m3), the combined pollution days would reach 111. The concentration of O3 in Zhuzhou and Xiangtan was about 10 μg/m3 lower than that in Changsha. Lower SO2 levels in Changsha might influence the partitioning of OH radicals and reactive nitrogen species, potentially affecting local O3 formation efficiency. NO2 and meteorological conditions jointly influence the co-variation in PM2.5 and O3, with NO2 playing a more significant role in PM2.5 formation. The long-term time series and daily concentrations of PM2.5 and O3 in the CZT showed opposing values, but there were short-term synergistic events on the scale of daily concentrations, and the time period was typically 3–10 days. Low humidity and strong sunlight may cause antagonistic events in which the concentration of O3 rises rapidly. Under static and stable weather conditions with low wind speed, no rainfall and moderate humidity, the concentration of PM2.5 and O3 rose alternately on sunny and cloudy days, demonstrating synergistic growth.