[Spatial and Temporal Variations in PM₁ Concentration and its Correlation with AOD in China from 2014 to 2017]

Based on the PM₁ mass concentration data from all the air quality monitoring stations in China from 2014 to 2017, the temporal and spatial distribution characteristics of PM₁ concentration were studied using the time series statistical and spatial hierarchical clustering methods, and the PM₁ spatiotemporal evolution characteristics were revealed. Combined with AOD data of the MODIS remote-sensing satellite, the temporal and spatial variation in PM₁-AOD correlation was analyzed on a fine scale. The results showed that, from 2014 to 2017, the annual average PM₁ concentration in China decreased yearly, the seasonal PM₁ concentration showed the characteristics of "high in winter and low in summer," and the monthly average PM₁ concentration showed a "U"-shaped variation. An "M"-shaped PM₁ variation pattern was presented before and after the holidays. Weekly variation showed that high PM₁ values occurred on Mondays and Fridays, and low ones occurred on Sundays. Based on the spatial clustering method, the national average annual PM₁ concentration in China was divided into seven categories, and the overall spatial distribution pattern was "high in the east and low in the west and high in the north and low in the south." The highest and the lowest values of average PM₁ concentration occurred in central China(54.59 μg·m^-3) and in Xinjiang-Qinghai-Xizang(11.37 μg·m^-3), respectively. The PM₁-AOD relationship was positively correlated as a whole, the highest correlation coefficient was 0.55 in central China, and the lowest value was 0.36 in central and southern China.