Abstract: The black carbon (BC) aerosol data of Baoji City, China were continuously monitored online from February 4 to 26, 2019 using AE-31 Aethalometer in this work, and then combined with the data of PM2:5 mass concentration, wind speed and direction, the variation of BC mass concentration and its sources during the pollution in this region were investigated by cluster analysis. The results shows that the average mass concentration of BC during the observation period is 2.8 µg·m−3, ranging from 0.4 to 8.0 µg·m−3, the average mass concentration of PM2:5 is 119.9 µg·m−3, ranging from 17.3 to 221.9 µg·m−3, and the average mass concentrations of BC and PM2:5 during heavy pollution are 3.4 µg·m−3 and 176.4 µg·m−3, respectively. When the air quality is ”good”, the daily variation of BC mass concentration has obvious peak; when the air quality is ”light pollution”, the daily variation of BC mass concentration is ”double peak and double valley” type; when the air quality is ”moderate and heavy pollution”, the daily variation of BC mass concentration shows a trend of low during the day and high at night. It is also shown that southeast and northeast wind directions have a strong influence on BC. Under gusty and non-gusty conditions, when the air quality is good, light, moderate and heavy pollution, the BC mass concentrations are 1.9 and 1.5 µg·m−3, 2.4 and 2.2 µg·m−3, 3.5 and 3.0 µg·m−3, 3.7 and 3.3 µg·m−3, respectively. It shows that the heavier the pollution, the greater the BC concentration, and the pollutants tend to accumulate under static wind conditions. Furthermore, backward trajectory clustering analysis shows that the air mass from the east of Baoji and the blocking effect of Qinling Mountains have a greater influence on the concentration of BC in Baoji.

Key words: black carbon aerosol, Baoji, heavy pollution, cluster analysis