Spatiotemporal patterns and spatial clustering characteristics of air quality in China: A city level analysis.

This study utilized air quality data on six pollutants (PM 2.5 , PM 10 , O 3 , CO, NO 2 , and SO 2 ) obtained by monitoring for one year (from Jan 1 to Dec 31, 2016) in 338 Chinese cities at or above the prefectural level, and introduced the comprehensive air quality index (CAQI). Specifically, the CAQI was used to measure the comprehensive status of ambient air quality, after which the spatiotemporal distribution of the CAQI and its spatial correlation and clustering were investigated at the month and year levels, respectively. The CAQI values were generally high nationwide, with remarkable spatiotemporal variations. Additionally, cities with higher (or lower) CAQI values were concentrated in north (or south) China, while those with higher CAQI values were also observed in west and east China. The CAQI values exhibited a U-shaped trend from January to December, with the highest values being observed in winter and spring and the lowest during summer. Moreover, particulate matter (PM 2.5 and PM 10 ) is the major pollutant during most of the year, with PM 2.5 being prevalent in east and central-south China and PM 10 in northwest and north China; CAQI values are highly dependent on particulate concentrations. During summer, O 3 becomes a major pollutant and contributes greatly to CAQI, with the highest O 3 being observed in the Bohai Rim, the middle and lower reaches of the Yellow River, and the eastern coast of China. Finally, there was significant spatial autocorrelation and clustering of the CAQI, with spatial hot spots of CAQI being observed in southwest Xinjiang province, where air pollution issues have not received a great deal of attention, as well in Beijing-Tianjin-Hebei (BTH) and its surrounding areas, while cold spots for CAQI are mainly in south and northeast China. [ABSTRACT FROM AUTHOR]