[Spatial-temporal Variation of Ozone Concentration and Its Driving Factors in China]

Based on the ozone monitoring data from 2015 to 2017, this study presents the spatial-temporal variation of the ozone concentration and its driving factors in major cities in China via Kriging interpolation, spatial autocorrelation analysis, hotspot analysis, and geographical detector. The results show that:① The ozone pollution became increasingly heavier from 2015 to 2017, with the number of cities in which the 90th percentile of daily maximum 8-h ozone concentration exceeded the air quality standard (GB 3095-2012) increased from 74 to 121, and the proportion of non-attainment days increased from 5.2 percent to 8.1 percent. ② Ozone pollution mainly happened from April to September, during which the non-attainment days contributed 87.5 percent to 95.3 percent to the yearly total number of ozone polluted days. From May to July, ozone concentrations increased the most dramatically, with the proportion of non-attainment days increasing from 10.6 percent in 2015 to 20.5 percent in 2017. Moreover, in 2017, 83.0 percent of the moderate ozone pollution and 91.0 percent of the severe ozone pollution happened from May to July. ③ With the ever increasing ozone concentration over the North China Plain, the high ozone polluted areas such as the Beijing-Tianjin-Hebei region and Yangtze River Delta urban agglomeration are connected geographically. They form the most highly polluted area in China, which includes the Bohai Rim region, Zhongyuan urban agglomeration, Yangtze River Delta urban agglomeration, Shanxi Province, Guanzhong area, and the middle part of Inner Mongolia. In addition, cities in Pearl River Delta region, Chengdu-and-Chongqing urban agglomeration, and the southern part of East China are also gathering speed in terms of ozone pollution, among which Chengdu-and-Chongqing urban agglomeration has become a new ozone-polluted center. ④ The spatial agglomeration of ozone concentration has been enhanced year by year with hot spots distributed mainly in the North China Plain and the middle and lower reaches of the Yangtze River. In contrast, there are cold spots in Northeast China, Southwest China, and Southern China. ⑤ The analysis results from geographical detector show that meteorological factors, industrialization, urbanization, and emissions of ozone precursors all have a significant effect on the distribution of the ozone concentration, but there are also discrepancies in the priority of the driving factors in different regions and seasons.