Ice nucleating particle sources and transports between the Central and Southern Arctic regions during winter cold air outbreaks

Ice nucleating particles (INPs) initiate ice formation, affecting the liquid versus ice distribution and radiative properties of clouds. INPs have been measured around the Arctic, but few INP concentration measurements have been reported for air during movement south out of central Arctic pack ice regions during cold air outbreaks (CAOs). We analyzed cases of transports connecting the Central Arctic location of the Multidisciplinary Drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition to the near sea ice edge in Svalbard and across ice-free ocean to the Cold-air Outbreaks in the Marine Boundary Layer Experiment (COMBLE) site at Andenes, Norway, during the 2019–2020 Arctic winter. Aerosol surface area concentration measurements during CAOs indicate a switch from primarily accumulation mode at MOSAiC toward marine coarse mode (from sea spray emissions) at COMBLE. INP concentrations were independent of aerosol surface area or volume over the pack ice in MOSAiC in winter. At Svalbard, INPs related best to supermicron aerosol surface area and supermicron volume. At the COMBLE site, INPs related best with total aerosol surface area and total aerosol volume. In 5 of 6 case studies analyzed, INP concentrations increased in association with the transition to a dominance of sea spray aerosols. The INPs at COMBLE had a unique INP concentration mode near −18°C and higher ice nucleation active site densities (e.g., INPs per surface area) compared to those previously reported for other open ocean regions dominated by marine aerosols. While the INP sources in this case appear to be from oceanic emissions from shallower oceans under turbid water conditions, attribution solely to sea spray aerosols versus mixing down of free tropospheric aerosols by CAO clouds remains as a future topic. These studies provide a basis for parameterization of INPs for numerical modeling studies of CAO cloud systems.