Source apportionment of black carbon in different seasons in the northern suburb of Nanjing, China

Abstract

In this study, black carbon (BC) was measured in the northern suburb of Nanjing from January to December 2016 using a seven-channel Aethalometer (AE33). BC sources in different seasons are quantified based on the Aethalometer model. The results indicate that the seasonal average BC concentration is 980 ± 810 ng/m3 (the average value ± the standard deviation), 1062 ± 986 ng/m3, 1168 ± 937 ng/m3 and 2117 ± 1549 ng/m3 during spring, summer, autumn and winter, respectively. The source apportionment results reveal that liquid fuel (e.g., traffic) has higher seasonal contributions (ranging from 70% in autumn to 84% in winter) to total BC concentrations than solid fuels do (e.g., coal and biomass, ranging from 16% in winter to 30% in autumn). The relative contribution of liquid fuel to total BC concentrations was higher in winter and summer, whereas solid fuel has higher contributions in autumn and spring. The diurnal variations in total BC concentrations and the contributions of liquid fuel revealed a major increase during traffic rush hours in all seasons. However, solid fuel has higher contributions to total BC concentrations from 22:00–4:00, particularly during autumn. Meteorological parameters (wind speed and wind direction) provide supportive evidence from BC sources that BC emissions are mainly from local traffic sources and industry coal combustion in the southeast. Moreover, long-range transport from the southwestern regions (mainly Anhui, Zhejiang, Jiangxi and Hunan) of the sampling site also plays a role in total BC concentrations, especially in autumn and winter. The episodes of high BC concentrations under high wind speed in winter are caused by long-range transport from Hebei and Shandong Provinces. High BC in June is from biomass burning activities in the southeastern region of Nanjing and Zhejiang Province.