Sources and processes governing the annual cycle of aerosol chemical composition in the central Arctic Ocean

Aerosols play a crucial role in the radiative balance of the Arctic, a place that is warming at faster rates than anywhere else on Earth. As a function of their physicochemical state (size, abundance, chemical composition, degree of aging and mixing state), aerosols can directly interact with the incoming solar radiation by absorbing or scattering light, and/or serve as seeds for cloud formation, thus indirectly modulating the amount of shortwave and longwave radiation respectively reaching and escaping the Earths surface. In the central Arctic Ocean, observations of the aerosols physicochemical characteristics have mostly been limited to summertime. As a result, large knowledge gaps remain on the role of aerosols in the central Arctic radiative budget throughout the year, in particular during the dark autumn and winter months, with great implications for model performances. Here, we present the first annual central Arctic Ocean observations of the chemical composition of submicron aerosols, as measured by a high-resolution time-of-flight aerosol mass spectrometer (AMS) during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. Measurements from the Arctic Ocean 2018 expedition close the summer data gap when no chemical composition measurements were available during MOSAiC. Based on the size-resolving and high-time resolution capabilities of the AMS, we further investigate the sources, emission processes, and potential radiative impacts of aerosols during the aerosol-sensitive autumn season. We find that episodic events of blowing snow and long-range transport of pollutants from lower latitudes are key contributors to the submicron aerosol and cloud condensation nuclei number concentrations, where blowing snow represents the only source of Aitken mode aerosols.Focusing on the spring and summer, we also present the results of a source apportionment study focused on the chemical and geographical sources of organic aerosols (OAs). Using a statistical method called positive matrix factorization, we find that anthropogenic OAs, of Eurasian origin, dominate the central Arctic Ocean OAs budget until at least the month of May. Warm air mass intrusions in mid-April are found to bring large amount of pollution to the central Arctic, with a chemical composition distinct from that of the background haze. Episodic bursts in naturally-sourced marine OAs, originating from the marginal ice-zone and open ocean regions, become increasingly important during summer.Together, the results from these studies will serve to greatly improve our understanding of aerosol sources and related physicochemical properties in the central Arctic Ocean, as well as their role in the central Arctic radiative budget.