Study on Concentration and Radiative Forcing of Black Carbon Aerosol in Suburban Nanjing

Black carbon (BC) is one of the most important absorbent aerosols in the atmosphere, and it has a significant impact on climate change. This study analyzed the concentration and seasonal variation of carbonaceous aerosols sampled on the Pukou campus of Nanjing University in 2008. With a box model coupled with OPAC (Optical Properties of Aerosols and Clouds) and TUV (Tropospheric Ultraviolet and Visible radiation model), the optical thickness and radiative forcing of BC were estimated on the basis of the sampling data. Investigations showed that the average concentrations of BC and organic carbon (OC) are 6.7±4.6 μg/m³ and 21.3±13.3 μg/m³, respectively, and the average ratio of OC/BC is 3.4. The mass concentration of BC is higher in winter and fall but lower in summer. The model calculation suggests that the annual mean optical depth and absorbing coefficient of BC are 0.07 and 44 Mm^-1, respectively. In a clear sky at noon, BC has a maximum instantaneous direct radiative forcing of -22.9±14.3 W/m² at the surface and 12.5±7.3 W/m² at the top of the atmosphere.