Characterization of size-resolved hygroscopicity of black carbon-containing particle in urban environment.

Abstract

The hygroscopic properties of BC-containing particles (BCc) is important to determine its wet scavenging, atmospheric lifetime and interactions with clouds. Such information is still lack in real world because of the challenges in isolating BCc from other aerosols to be directly characterized. In this study, the size-resolved chemical components of BCc including the refractory BC core and associated coatings were measured by a soot particle-aerosol mass spectrometer in suburban Nanjing. The size-resolved hygroscopicity parameter of BCc (κBCc) is obtained based on this full chemical characterization of BCc. We found increased inorganic fraction and more oxidized organic coatings when being more thickly coated, which modified κBCc besides the determinant of particle size. The bulk κBCc was observed to range at 0.11-0.34. The size-resolved κBCc consistently showed minima at coated diameter (Dcoated) 100 nm, parameterized as κ(x)=0.28-0.35×exp(-0.004×x), x=Dcoated. Under critical supersaturation (SS) 0.1% and 0.2%, D50 of BCc was at 200 ± 20 nm and 135 ± 18 nm respectively. On average 33 ± 16% and 59 ± 20% of BCc in number could be activated at SS = 0.1% and 0.2% respectively. These results provide constraints on surface CCN sources for the light-absorbing BC-containing particles.