Evolution of atmospheric black carbon and effect of model parameters on source apportionment in Shanghai

Black carbon (BC) is an atmospheric pollutant with short life but strong light-absorbing capacity, which can affect human health and climate change. Analysis of BC sources can help develop mitigation strategies and provide short-term climate benefits. In this study, the differences in BC level and source between urban and suburban sites in Shanghai were investigated from January 2016 to December 2016. In addition, the effects of Ångström exponent values and wavelength combinations on BC source apportionment were evaluated. The results showed BC concentrations tend to be lowest in the urban core (PD site, 1.48 ± 0.94 μg m⁻³) and increase towards the outer areas (QP site, 2.74 ± 1.73 μg m⁻³) of the city. Since fossil fuels contributed more than 90% of total BC in all seasons, the higher BC level in suburban areas could be attributed to the traffic emissions of heavy vehicles due to the relaxed traffic policy. The lowest average BC concentrations appeared in summer and autumn and the highest BC concentrations were measured in winter. But small peaks of BC concentrations were observed in July 2016. Compared to wavelength combination, the variation of Ångström exponents had a more significant influence on the BC source apportionment. Furthermore, the change in Ångström exponent of fossil fuels had a greater impact than that of biomass combustion.