Mixing state of black carbon at different atmospheres in north and southwest China

Large uncertainties remain when estimating the radiative forcing by black carbon (BC) because the corresponding microphysical properties have not been well addressed. In this study, the BC size distributions were studied based on three different field campaigns at an urban site, a suburban site, and a background site in China using a single particle soot photometer (SP2) in tandem with a differential mobility diameter. Measurement results indicate that the BC particles were composed of either thinly or thickly coated aerosols. The mean number fractions of the thinly coated BC aerosols were 51 %, 67 %, and 21 % for the urban, suburban, and background sites, respectively. The corresponding thickly coated (thinly coated) core mass median diameters were 187 (154), 182 (146), and 238 (163) nm, respectively. The mean diameter of the thickly coated BC-containing aerosols was larger than that of the thinly coated BC-containing aerosols, while the mean BC core diameter of the thickly coated BC-containing aerosols was smaller than that of the thinly coated BC-containing aerosols. About 10 % of the BC-containing aerosols with the BC core are attached to the other non-BC components, which were mainly generated by coagulation between the BC and non-BC components. The measurement results in our study can be further used in modeling studies to help with constraining the uncertainties of the BC radiative effects.

Automated summary

This study investigates the size distributions of black carbon (BC) particles in urban, suburban, and background sites in China. The results show that the BC particles were composed of thinly or thickly coated aerosols. The mean number fractions of thinly coated BC aerosols were highest in the suburban site and lowest in the background site. The study also found that about 10% of the BC-containing aerosols were attached to non-BC components. These findings can be used in modeling studies to better understand the uncertainties of the BC radiative effects.