Chemical and Microphysical State of the Central Arctic Atmosphere

The Arctic is warming three times faster than the rest of the planet. Increased areas of open ocean and changes in atmospheric transport pathways affect the Arctic atmospheric chemical and microphysical state, which themselves can modulate cloud, precipitation, and radiation processes. The Arctic aerosol and trace gas regime features strong seasonal variations. Arctic winter is dominated by long-range transported mid-latitude anthropogenic emissions resulting in arctic haze, while summer is characterized by more local and natural trace gas and aerosol sources. Aerosols and trace gases have been shown to be important for the Arctic radiative balance, inducing an overall net positive radiative forcing through direct radiation interactions. In-situ observations are, however, scarce, especially during transition seasons (spring and autumn) owing to the difficulty of performing measurements in the high Arctic at this time of year. A full suite of state-of-the-art instrumentation (trace gases surface concentration, aerosol number size distribution, aerosol mass composition, cloud condensation nuclei number) was deployed onboard RV Polarstern during the year-round Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. Here, we focus on the autumn 2019 and spring 2020 observations to present an overview on the chemical and microphysical state of the central Arctic atmosphere during transition seasons, where air mass origin can vary strongly. We compare changes in the aerosol mass composition in terms of organic and non-organic components including black carbon. The variation in the aerosol chemical composition affects the particles acidity and hygroscopicity, and thereby gas-particle partitioning. All together these features result in different behaviour of cloud condensation nuclei number and activation patterns between the two transition seasons.