Characteristics and Source Apportionment of Black Carbon in Chengdu

Abstract

Black carbon (BC) was measured at Chengdu from December 1, 2017, to November 30, 2018, using a seven-channel aethalometer (AE-33). The variation characteristics of BC were obtained. BC sources were explored based on the aethalometer model and a hybrid single particle Lagrangian integrated trajectory model (Hysplit-4). The results showed the BC concentration was the highest in the winter (8.18 μg·m-3) with the monthly mean of 11.11 μg·m-3 peaking in December, followed by the spring (5.11 μg·m-3) and autumn (3.91 μg·m-3), and was the lowest in summer (3.28 μg·m-3) with the lowest monthly mean of 2.30 μg·m-3 in July. The annual average concentration of BC was 5.26 μg·m-3 with a standard deviation of 4.27 μg·m-3. The diurnal variations of BC showed typical bimodal patterns in four seasons mainly due to the influence of the boundary layer and traffic rush. The source apportionment of BC showed that the liquid fuel (e.g., vehicle emission) had higher contribution to total BC concentration during all seasons (ranging from 69% in winter to 82% in summer) than solid fuel (e.g., coal and biomass combustion). The contribution of liquid fuel to the total BC was higher in summer, while solid fuel had a higher contribution in winter. The diurnal cycles of BC source apportionment demonstrated that the contribution of liquid fuel increased in the rush hours. The results of potential source contribution function and concentration weighted trajectory showed that the potential sources of BC in Chengdu were slightly different in different seasons and were mainly affected by the different air mass sources. However, the main potential source regions were the surrounding areas of Chengdu and the areas between Chengdu and Chongqing (the Chuanyu City group). The mass contribution to the BC in Chengdu was high in the region where liquid fuel most affected the total BC. Additionally, the southern part of Shaanxi and the southern part of Gansu were also potential sources of BC, and in Summer, some regions in Guangxi and Guizhou could become the source regions of BC in Chengdu.