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

Abstract

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 PM 2.5 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 BCcontaining 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 BCcontaining 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.

Recent Advances in Quantifying Wet Scavenging Efficiency of Black Carbon Aerosol

“…Nanling, and Mt. Sonnblick [37,40,80]. Despite the variability, MSEs of BC are generally lower at low-altitude regions (urban, suburban, and rural sites) and increase with rising altitude (p < 0.05).…”

“…The SE is defined as the mass/number fraction of BC in cloud droplets, representing the fraction of BC scavenged in-cloud (Equation (1)) [40].…”

“…The mass concentration of BC can be conventionally measured by online instruments such as aethalometer (AE), single particle soot spectrometer (SP2), particle soot/absorption photometer (PSAP), continuous soot monitoring system (COSMOS), and soot particle aerosol mass spectrometer (SP-AMS) [56][57][58][59][60]. The number concentration of BC-containing particle can be quantitively determined by SP2 or semiquantitatively by a single particle mass spectrometer (SPMS) [40,58]. The detailed measurement technologies of While numerous studies have focused on the wet scavenging of BC, there is still no comprehensive review specific for this topic.…”

“…Schroder et al [39] found that BC-containing particles with 85-nm cores can only be activated after being coated thicker than 80 nm. Zhang et al [40] pointed out that mixing state is a key factor that influence the SE of BC under low LWC (< 0.1 g m −3 ) condition. The internal mixing with sulfate (rather than organic materials) improves the incorporation of BC particles into cloud droplets [40].…”

“…The mass scavenging efficiency (MSE) is widely applied to express the in-cloud scavenging ability for aerosols [36]. MSEs of BC were observed to be in a wide range over the world [37][38][39][40], and the influencing factors were attributed to physical and chemical properties (e.g., size and chemical compositions) [41,42], and meteorological conditions (cloud water content, temperature, etc.) [43][44][45].…”