Black Carbon scavenging in liquid Arctic clouds: the role of size and mixing state

Abstract: Black carbon (BC) contributes to Arctic warming by absorbing sunlight and darkening snow. Its atmospheric lifetime critically determines its concentration and climate impact, yet the processes controlling its removal remain poorly constrained in the Arctic. From 18 months of single-particle measurements at the Zeppelin Observatory (Svalbard), we analysed 37 liquid cloud events (~200 hours) to investigate the link between BC properties and in-cloud scavenging, providing the most extensive in-cloud single particle BC dataset to date. While large BC cores (DrBC>200 nm) were consistently scavenged, smaller cores were only partly removed. However, even thin soluble coatings significantly enhanced their scavenging, showing that mixing state modulates BC scavenging in the CCN-limited regime typical of Arctic low-level clouds. Seasonal variability in clear sky BC mixing state further suggests corresponding changes in scavenging efficiency. Our results demonstrate that besides size, the size-resolved BC mixing state is a key variable for BC scavenging in the Arctic and models should take it into consideration to accurately predict BC-cloud interaction.