Abstract: China has been witnessing the rapid development of industrialization and urbanization in recently years. As a consequence, it suffers from air pollution, notably haze. Based on the data for PM2.5 from 189 automatic air quality monitoring stations of the urban agglomeration in the Middle Reaches of the Yangtze River from January 2015 to February 2016, this paper applied ordinary Kriging interpolation method, exploratory spatial data analysis and relevant correlation coefficient method to investigate the spatio-temporal characteristics and influencing factors of PM2.5 of municipalities of the Middle Reaches of the Yangtze River from year, season and month time scales. The findings are the following. (1) On the year time-scale, the distribution of PM2.5 concentration within the Middle Reaches of the Yangtze River exhibits high values in the north and low values in the south, local projecting. The average value of PM2.5 concentration was 55.28 μg/m3 in the whole study area. Specifically, Hubei province has the highest average value of PM2.5 concentration with 68.17μg /m3, followed by Hunan province with an average value of 53.66 μg/m3. Jiangxi province has the lowest average value of PM2.5 concentration with 44.01 μg/ m3. (2) On the season time-scale, PM2.5 concentration of the Middle Reaches of the Yangtze River presented significant seasonal variations, specifically, high values in both spring and winter, and low values in both summer and autumn. The seasonal variations are closely correlated with the regional climate conditions, specifically, high temperature and precipitation in summer, low temperature and precipitation in winter. (3) On month time-scale, PM2.5 concentration showed a U-shaped curve. Specifically, it reached the summit in January, continued to decline and then went down to the bottom in June, finally increased gradually from July. (4) NO2、CO were two main   air pollutants factors affecting PM2.5 concentration. Moreover, precipitation and relative humidity were two main important meteorological factors affecting PM2.5 concentration.
Key words：PM2.5 concentrations; spatio-temporal characteristics; meteorological factors; the urban agglomeration in the Middle Reaches of the Yangtze River