Assessing the causal effects of ozone precursors, meteorological variables, and urbanization-related factors on ground-level ozone across China.

Ozone pollution has become increasingly severe in China, particularly in megacity clusters. To comprehensively assess the impacts of environmental factors on ozone, this study employs Convergent cross mapping and Geographical Convergent Cross Mapping models to quantify the causal effects of ozone precursors, meteorological variables, and urbanization-related factors on ground-level ozone across China. Results show that the causal effects of nitrogen dioxide (NO2) and formaldehyde (HCHO) on ozone varied with the HCHO/NO2 ratio, peaking under VOC-limited regimes; NO2 generally exerts a stronger influence than HCHO. Solar radiation, temperature, cloud cover, and relative humidity were identified as the dominant meteorological drivers. Solar radiation and temperature exerted short-lagged effects, whereas wind-related variables showed longer lags in the Pearl River Delta but shorter lags in the Sichuan Basin. Urbanization-related factors, including impervious surfaces, industrial land, and road network, exhibited significant causal effects on ozone, with causal strengths varying across regions and over time, and were strongest in the Pearl River Delta. These findings advance understanding of the causal links between spatiotemporal environmental factors and ozone, emphasizing the importance of region-specific emission control strategies to effectively mitigate ozone pollution.