Airborne investigation of black carbon interaction with low-level, persistent, mixed-phase clouds in the Arctic summer

• Main Authors: Zanatta, Marco, Mertes, Stephan, Jourdan, Olivier, Dupuy, Regis, Järvinen, Emma, Schnaiter, Martin, Eppers, Oliver, Schneider, Johannes, Jurányi, Zsófia, Herber, Andreas
• Format: Text
• Language: English
• Published: 2023
• Subjects: Arctic; Svalbard; black carbon; Sea ice
• Online Access: https://doi.org/10.5194/acp-2023-30; https://acp.copernicus.org/preprints/acp-2023-30/

Aerosol-cloud interaction is considered one of the largest sources of uncertainties in radiative forcing estimations. To better understand the role of black carbon aerosol as cloud nucleus and the impact of clouds on its vertical distribution in the Arctic, we report airborne in-situ measurements of refractory black carbon aerosol particles (rBC) in the European Arctic near Svalbard during the ACLOUD campaign held in summer 2017. rBC was measured with a single particle soot photometer on board of the research aircraft “Polar 6” from the lowest atmospheric layer up to approximately 3500 m asl. During in-cloud flight transects, rBC particles contained in liquid droplets (rBC residuals) were sampled through a counterflow virtual impactor (CVI). Overall, the presence of low-level clouds was associated with a radical change in the concentration and size distribution of rBC particles in the boundary layer compared to the free troposphere. Four flights conducted in the presence of inside-inversion, surface-coupled, mixed-phase clouds over sea ice, were selected to address the variability of rBC particles sampled above, below and within the cloud layer. We show that the properties of rBC such as concentration, size and mixing state drastically changed from the above to the below cloud layers, but also within the cloud layers from cloud top to cloud bottom. Our results might suggest the occurrence of a cloud-mediated transformation cycle of rBC particles in the boundary layer which includes activation, cloud processing, and sub-cloud release of processed rBC agglomerates. In the case of persistent low-level Arctic clouds, this cycle may reiterate multiple times, adding one additional degree of complexity to the understanding of cloud processing of black carbon particles in the Arctic.