Overview of Atmospheric Aerosol Observations during the ATWAICE Expedition in the Central Arctic

Understanding aerosol particles in the Arctic is crucial due to their impact on the region’s radiative balance and their role in modifying cloud properties. These interactions drive unique feedback mechanisms that enhance Arctic warming and influence global climate systems. Consequently, it is important to identify and quantify Arctic aerosol particle sources and sinks, including their vertical transport, and to characterize their optical properties and resulting effects on cloud formation. Despite the importance of aerosol particles in the Arctic, there is a lack of direct measurements of aerosol particles over the Arctic especially over the Arctic marine boundary layer. In this context, we have conducted aerosol measurements aboard the German research vessel Polarstern during the ATWAICE (Atlantic Water Pathways to the Ice in the Nansen Basin and Fram Strait) expedition from June to August 2022. This study included continuous measurements of physical and chemical aerosol parameters to investigate variations in aerosol properties. On-line measurements of black carbon (BC) and its mixing state were complemented by off-line analyses of seawater and fog water samples to identify transport pathways of BC particles. Additionally, seawater, aerosol filter samples, and fog water samples were analyzed to explore how ice nucleating particles are linked across these compartments. Vertical profiles of aerosol particles were measured above different surface conditions to examine the direction of vertical particle transport. Higher aerosol concentrations were recorded as the ship passed through the outer margin of the marginal ice zone, where marine sources dominate, supported by evidence of significant photochemical ageing processes. The highest values of refractory black carbon (rBC) and light scattering coefficients were measured during the transact from northern Europe to the Arctic circle (between 56°N to 70°N), with average rBC concentrations of approximately 40 ng m^-3 and light scattering at 525 nm averaging ~29 Mm^-1. During this period, air mass trajectories reflected a nearly equal influence from both continental and marine sources. In contrast, the lowest scattering and absorption values were observed in the central Arctic, when the ship navigated in densely packed ice regions under the influence of north-easterly air masses originating over the Arctic Ocean. A comprehensive analysis of these findings will be presented in this presentation.