Black carbon (BC) is an important component of atmospheric particulate matter (PM) emitted during the combustion process. Light absorption and scattering exhibited by BC affect the exchange of solar energy on Earth. In this study, continuous measurements of atmospheric particulate BC were carried out, using a BC analyzer (AE33) in the suburban area of Nanjing from January 2019 to May 2019, to realize the diurnal variations of BC during the different seasons and potential sources of BC during the clean (CD, PM2.5<35 μg ·m-3) and haze days (PD, PM2.5>75 μg ·m-3). The results showed that the average concentration of BC was (3.8±2.3) μg ·m-3; a higher average BC concentration value of (4.3±2.6) μg ·m-3 was observed during the winter, exceeding that during the spring period by a factor of 1.3. The higher BC concentrations during the winter was attributed to the stagnant weather conditions and additional emissions. Significant diurnal cycles of BC were observed with higher BC concentrations during rush hours of traffic, suggesting traffic origins. The Ångström exponent were 1.32 and 1.30 during the spring and winter periods, respectively, indicating that the BC was mainly produced from the traffic emissions during both the seasons. This hypothesis was also supported by the average BC/CO ratio of 0.005, which was similar to that of BC derived by traffic emissions. Moreover, we discovered that the contributions of traffic emissions to BC were 68%-87% and 72%-86% during the haze and clean periods, respectively. This indicated enhanced contributions of coal combustion and biomass burning to BC in Nanjing during the haze events. Finally, using the potential source contribution function (PSCF) and concentration weighted trajectory (CWT) analysis, we highlighted that the BC at the receptor site was mainly from the local emissions in the surrounding areas of Nanjing.
Keywords: Nanjing; aethalometer; black carbon aerosol; concentration weighted trajectory (CWT); potential source contribution function(PSCF); Ångström exponent.