Spatial and temporal distribution characteristics of urban air quality index during haze pollution episodes in China

This study adopted the monitoring data of Air Quality Index (AQI) from 1165 environmental monitor stations in 19 city clusters of China. The data in spring and winter time from 2015 to 2020 were selected in this paper. By cross validation, the optimal spatial interpolation method was chosen to analyze the spatial and temporal distribution characteristics of AQI during haze period in spring and winter time in the recent 6 years in China. Then, using spatial autocorrelation method and empirical orthogonal function method, the spatial heterogeneity of the data and the change trend and variation rules of AQI over daytime and nighttime was analyzed. The results showed that in the spring and winter of the recent 6 years, except the spring in 2015, the AQI in nighttime was worse than that in daytime. The high value area of AQI was decreasing, which indicated that the air quality was becoming better. The AQI spatial correlation of these 19 cities was significant, and the diurnal and nocturnal hot spot area in spring and winter time increased first and then decreased gradually from 2015 to 2020; the air pollution in winter is more serious than that in spring. The change of air pollution in daytime and nighttime had similar trends. From the west to east, North China to Central China, Central East China and Central South China, the change of air pollution in daytime and nighttime had similar trends, which showed an expansion trend.