National air pollution distribution in China and related geographic, gaseous pollutant, and socio-economic factors.

Regional specification of PM2.5 pollution characteristics is crucial for pollution control and policymaking. Spatiotemporal variations of six criteria air pollutants and influencing factors in China were studied using hourly concentrations of PM2.5, PM10, SO2, NO2, CO, and O3 from 2015 to 2016. China was categorized into eight regions: north-east, northern coastland, eastern coastland, southern coastland, Yellow River middle reaches, Yangtze River middle reaches, south-west, and north-west. The 29 exemplary cities in China were also researched. It was found that the PM2.5 concentration in the northern coastland (Beijing-Tianjin-Hebei-Shandong) was the highest (72.28 μg.m-3) among the eight regions, particularly in the city of Baoding, Hebei, which had an annual average PM2.5 concentration of 98.53 μg.m-3. Average PM2.5 concentrations in 2015 and 2016 of China were 50.16 μg.m-3 and 46.61 μg.m-3, respectively. Compared with 2015, the PM2.5 concentration decreased by 8.41% in 2016, the decline of PM2.5 in summer was the largest, followed by autumn, spring and winter. The average mean PM2.5 concentrations of the 29 exemplary cities in 2015 and 2016 were 54.66 μg.m-3 and 48.37 μg.m-3, respectively, exceeding the limit for grade 2 of the national standards (35 μg.m-3). National air pollution distribution has exploded geographically with influence of regional economic factors. Gaseous pollutant as well as geographical and socio-economic conditions influenced PM2.5 emissions. Effects of these factors on PM2.5 emissions varied across regions and decreased continuously from the northern region to the south-west and eastern coastland regions. This paper clearly identifies the regional characteristics and distribution of PM2.5, focusing on the effects of gaseous pollutant, geography and socio-economic development. Secondary transformation and vehicle exhaust across regions should be further studied.