Temporal Evolution and Main Influencing Factors of Black Carbon Aerosol in Nanjing

Abstract

Temporal evolution of black carbon (BC) in Nanjing was studied along with its main influencing factors. The multi-wavelength aethalometer (AE-33) was used to select the typical month of each season to observe BC mass concentration, combined with atmospheric pollutant data, meteorological elements, and boundary layer detection data. Seasonal, daily, weekly trends, and source characteristics of BC were analyzed. The results showed that the BC concentration in Nanjing had obvious seasonal changes, which were higher in spring and winter, in the decreasing order:spring[(3351±919) ng·m-3] > winter[(3234±2102) ng·m-3] > in autumn[(3064±967) ng·m-3] > summer[(2632±1705) ng·m-3]. The diurnal changes in BC during the four seasons are bimodal, with peaks at 06:00-08:00 and 21:00-23:00. The morning and evening peak distribution characteristics of BC in different seasons are different. The peak concentration of BC was highest in the early morning peak spring and the highest in the late peak winter. The morning peak timing of winter is 2 h behind other seasons, while the summer peak timing is 2 h ahead of other seasons. The effect of the wind speed on the seasonal distribution of BC diurnal variation is significantly larger than that on RH. The mechanism of the influence of the inversion layer on the concentration of atmospheric pollutants is complicated. The effects of height, thickness, and temperature of the inversion layer on the pollutants are different in different seasons. Weekly BC effects vary seasonally. The effect of RH and wind speed on the weekly BC effect is small, and the difference in the inversion layer is the main reason behind it. Liquid fuel combustion in Nanjing has a greater contribution to BC, whereas solid combustion contributes by a lesser extent.