Fig. 1: Correlation between temperature and ozone concentration.

Spatial distribution of the correlation between daily average temperature and maximum daily 8-h running average ozone concentration across monitoring sites in China (a) and the United States (b) from April to October, 2015–2022. Circles in different colors indicate the correlation between temperature and ozone concentration. The colors transition from blue to red, representing a shift from negative to positive correlations, with blue indicating negative correlation and red indicating positive correlation. Circles, squares, and triangles represent significant positive correlation, significant negative correlation, and no significant correlation, respectively. The significance level is generally set at p < 0.05.