Characteristics and potential sources of black carbon particles in suburban Nanjing, China

As an important species of ambient fine particles, black carbon (BC) has significant adverse effects on air quality, human health and climate. This work reports results of one-year measurement of BC conducted in northern suburb of Nanjing, China from December 2017 to November 2018. Annual mean BC concentration was determined to be 2.78 μg/m³. BC concentration presented a “U” shape from December to November, lowest in summer and highest in winter. Nighttime BC concentration on average was higher than it in daytime, indicating heavier influence of meteorology than emissions. Diurnal pattern revealed that besides a clear emission-induced morning peak, meteorology played a more important role in governing BC changes in the rest of the day. Influences of meteorological factors on BC were in an order of boundary layer height, wind speed, temperature and relative humidity (RH), and further Granger causality analysis verified that the first three factors were indeed Granger causes of BC, while RH was not. Based on the diagnostic mass ratios of BC to CO, NO2 and SO2, as well as their correlation coefficients, we inferred that diesel vehicles rather than gasoline vehicles were the major BC emission source in suburban Nanjing; contributions from industry coal combustion were relatively less important. Back trajectory and potential source contribution analyses showed that regional rather than long-range transported air parcels led to the BC pollution in this site. Our findings provide useful insights into the reductions of BC and air pollution in this and similar atmospheric environments.