Analysis of air quality variation characteristics and circulation influence in Southern Sichuan Urban Agglomeration

Based on the air quality index (AQI) data and NECP/NCAR reanalysis data, combined with the distribution heterogeneity coefficient (C_V) within the year, the characteristics of air quality variation and its relationship with atmospheric circulation in Southern Sichuan Urban Agglomeration in 2020 were analyzed. The results showed as follows. 1) The AQI value of Southern Sichuan Urban Agglomeration decreased as a whole, the air quality in summer and autumn was better than that in spring and winter; C_V rose slightly, and the uneven distribution of air quality within the year increased. Among them, the difference of air quality distribution was the biggest in winter and the smallest in summer, and the regional difference was larger in the west of Southern Sichuan Urban Agglomeration than that in the east. 2) Due to the effect of primary pollutant PM_2.5, the spatial distribution of AQI was high in the middle and low around, and combined with the influence of PM₁₀, the spatial distribution of AQI had obvious seasonal differences. The spatial variation characteristics of spring and winter were similar, forming a high value area in the middle and a low value area in the north, high in the west and low in the east in summer and high in the southeast and low in the northwest in autumn. 3) When the urban agglomeration in Southern Sichuan Urban Agglomeration was in the upper trough in spring and winter, the accumulation of cold air was not conducive to the occurrence of convection, and the pollutant discharge was not smooth, resulting in the high AQI values in the two seasons. In summer and autumn, due to the existence of subtropical high and low trough in mid-high latitude, it was easy to generate convection and precipitation. In addition, the convergence situation of wind field was obvious, and the pollutants were not easy to accumulate, so the AQI was low.