Articles | Volume 17, issue 24
https://doi.org/10.5194/acp-17-14975-2017
https://doi.org/10.5194/acp-17-14975-2017
Research article
 | 
19 Dec 2017
Research article |  | 19 Dec 2017

The single-particle mixing state and cloud scavenging of black carbon: a case study at a high-altitude mountain site in southern China

Guohua Zhang, Qinhao Lin, Long Peng, Xinhui Bi, Duohong Chen, Mei Li, Lei Li, Fred J. Brechtel, Jianxin Chen, Weijun Yan, Xinming Wang, Ping'an Peng, Guoying Sheng, and Zhen Zhou

Abstract. In the present study, a ground-based counterflow virtual impactor (GCVI) was used to sample cloud droplet residual (cloud RES) particles, while a parallel PM2.5 inlet was used to sample cloud-free or cloud interstitial (cloud INT) particles. The mixing state of black carbon (BC)-containing particles and the mass concentrations of BC in the cloud-free, RES and INT particles were investigated using a single-particle aerosol mass spectrometer (SPAMS) and two aethalometers, respectively, at a mountain site (1690 m a. s. l. ) in southern China. The measured BC-containing particles were extensively internally mixed with sulfate and were scavenged into cloud droplets (with number fractions of 0.05–0.45) to a similar (or slightly lower) extent as all the measured particles (0.07–0.6) over the measured size range of 0.1–1.6 µm. The results indicate the preferential activation of larger particles and/or that the production of secondary compositions shifts the BC-containing particles towards larger sizes. BC-containing particles with an abundance of both sulfate and organics were scavenged less than those with sulfate but limited organics, implying the importance of the mixing state on the incorporation of BC-containing particles into cloud droplets. The mass scavenging efficiency of BC with an average of 33 % was similar for different cloud events independent of the air mass. This is the first time that both the mixing state and cloud scavenging of BC in China have been reported. Our results would improve the knowledge on the concentration, mixing state, and cloud scavenging of BC in the free troposphere.

Short summary
The mixing state of black carbon (BC)-containing particles and the mass scavenging efficiency of BC in cloud were investigated at a mountain site (1690 m a.s.l.) in southern China. The measured BC-containing particles were internally mixed extensively with sulfate, and thus the number fraction of scavenged BC-containing particles is close to that of all the measured particles. BC-containing particles with higher fractions of organics were scavenged relatively less.
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