Abstract:Based on daily air pollution data, meteorological observation data and sounding data from Weather Station of Shapingba in Chongqing, and the NCEP/NCAR reanalysis data during 2014-2018, the characteristics of monthly, seasonal and annual AQI, different air pollutant concentration and the day numbers with different air pollutant concentrations are analyzed systematically. Besides, the 500 hPa geopotential height field, 850 hPa wind field, vertical velocity field and the skew T-lnp diagram of heavy pollution days are also analyzed. The results show that the monthly variation of AQI in Chongqing is W-shaped, while those of PM2.5, PM10 and CO are U-shaped, and that of O3 is inverted U-shaped. Except that the concentration of O3 is the highest in midsummer, the concentrations of other pollutants are so high in December and January that the air quality becomes the worst in the two months. The concentration of O3 shows an increasing trend but other pollutants major decreasing year by year, and the air quality was significantly improved. PM2.5 was the main pollutant in Chongqing, especially in winter. PM10 pollution increases in spring, NO2 pollution mainly occurs in early spring and late autumn, and O3 pollution mainly appears in midsummer. Air pollution usually happens in winter. The meteorological diffusion condition is poor in Chongqing when the circulation in the middle and high latitudes of Eurasia in the middle troposphere has a distribution of low in the north and high in the south, and the cold air force is so weak that the lower troposphere is dominated by the south wind in most of the southern region. The condition is favorable for diffusion and clearance of air pollutant when the circulation in the middle and high latitudes of Eurasia in the middle troposphere has a distribution of high in the north and low in the south, and the meridional circulation is obvious. The rising convergence of water vapor is so weak that the relative humidity of the lower troposphere is low on heavy pollution days. The near-surface inversion layer and the thin wet layer maintain for a long time making atmospheric stratification relatively stable, which is the key of development and maintenance of air pollution in Chongqing.