Abstract: Using the aerosol optical depth (AOD) data of five observation stations located in Beijing, China, urban area and the air quality grades data in the region from January to December 2021, the quantitative relationship between AOD and air quality grades was studied, and the evolution characteristics of different types of aerosol particles, including black carbon (BC), urban-industrial aerosols (UI), desert dust (DD), and mixed aerosols (MT) under different air quality grades were analyzed. The results show that: (1) In 2021, the air quanlity in the urban area of Beijing was predominantly classified as moderate (50.7%) and light pollution (21.9%), the monthly variations in AOD exhibited a significant correlation with changes in air quality grades, the months with poor air quality including March, July and August, corresponded to the monthly peak and sub-peak values of AOD. (2) In the order of air quality from good to heavily polluted grades, the average AOD values for the five sites were 0.10, 0.51, 0.68, 0.87, and 1.23, respectively. (3) The dominant aerosol particle types varied with different air quality grades. In general, under good air conditions, the majority of days were dominated by BC, accounting for over 80%, and the remaining days were dominated by MT. As the air pollution increased , the proportions of days dominated by UI, DD, and MT increased, while the proportion of days dominated by BC decreased. Under lightly polluted level, the proportion of days dominated by MT was the highest, while under the heavily polluted level, the proportion of days dominated by DD was the highest.

Key words: solar radiometers, aerosol optical depth, air quality grades, aerosol particle types