Characterization of black carbon aerosol in the Yangtze River Delta, China: Seasonal variation and source apportionment

Abstract

As a crucial absorptive component of aerosols, black carbon (BC) plays a key role in modifying the planetary boundary layer (PBL) meteorology and hence aggravating the haze pollution. In this study, using the seven-channel Aethalometer model AE-33, the equivalent BC aerosols were continuously observed for one year in a typical city of Nanjing in the Yangtze River Delta (YRD). Together with the pollutant data of PM2.5 and trace gases (NO2, SO2, CO and O3), and the methods of potential source contribution function (PSCF) and concentration weighted trajectory (CWT) models, the spatiotemporal distribution and source apportionment of BC mass concentrations in Nanjing are discussed. It had large discrepancies in monthly and seasonal variations of BC concentrations, which were found to be the highest in December (3109.4 ± 1875.0 ng m−3) and the lowest in September (1300.8 ± 1031.6 ng m−3). Meanwhile, the BC concentrations ranked in the order of winter (2619.5 ± 1576.8 ng m−3) > spring (2142.4 ± 1219.3 ng m−3) > summer (1645.6 ± 1229.7 ng m−3) > autumn (1583.1 ± 1333.1 ng m−3). The diurnal variation of BC exhibited bimodal distributions in four seasons, peaking at 07:00–09:00 and 20:00–23:00, respectively. Fossil fuel BC (BCff) was calculated to contribute 71–77% to BC concentration. Long-range transport of BC was noticed mainly across inland China of North China Plain (NCP) and Twain-Hu regions in winter, and from the eastern YRD and southern PRD regions in summer. Overall, BC in Nanjing mainly originated from the surrounding cities in YRD, which had a maximum contribution more than 2000 ng m−3. The potential sources of BC varied significantly in the four seasons.