What have we learned from one year of aerosol observations in the central Arctic during the MOSAiC expedition?

The central Arctic ocean (CAO) is transforming rapidly due to climate change with wide spread consequences. Therefore, understanding the mechanisms of change, in particular related to the surface energy budget, is indispensable. Aerosols affect the surface radiation budget both directly and indirectly through interactions with clouds.In the CAO, cloud formation and radiative processes are particularly susceptible to aerosols, because their number concentration can be very low. To date, the climatic effects of aerosols in the CAO have mostly been constrained in terms of anthropogenic emissions and direct radiation interactions, where a significant warming contribution has been found. What is missing, are effects of natural aerosols and aerosol-cloud interactions. It is hence of utmost importance to fully understand the present-day aerosol-climate interactions, constrain the most relevant processes and how they relate to Arctic change in order to anticipate future impacts.However, the CAO is an inherently difficult place to study due to its limited physical accessibility as well as hampered satellite observations. To mitigate the observational scarcity, the "Multidisciplinary Observatory for the Study of Arctic Change" (MOSAiC) expedition drifted for one year between fall 2019 and 2020 in the CAO. In this contribution, we will present our insights from one year of aerosol observations that include variables such as cloud condensation nuclei and ice nucleating particle number concentrations, particle number size distributions, bulk and single particle chemical composition as well as optical properties. This presentation will specifically focus on unprecedented insights, for example the roles of processes like blowing snow and sea spray emissions and warm air mass intrusions, as well as the abundance of biogenic and biological aerosol components.