| Summary: | International audience The composition of the atmosphere in the central Arctic that is in contact with sea ice is controlled by a mix of natural and anthropogenic processes/sources. For example, emissions that originate from the cryosphere (sea ice, snow on sea ice, and leads) control the naturally varying background atmospheric chemistry state. In contrast, episodes of pollution transport from mid-latitude sources can bring large quantities of air pollutants to the central Arctic. We model atmospheric composition (trace gases, aerosols, clouds) during the spring 2020 season using a version of the regional WRF-Chem 4.1.1 model that has been modified to include halogen emissions from snow on sea ice, and is able to represent the influence of the cryosphere on the natural background state of atmospheric composition. We investigate the spring 2020 season, which included both conditions characterized by natural background atmospheric chemistry (Arctic Ocean/cryospheric emissions) as well as episodic transport of air from lower latitudes including pollution transport from Europe to the Central Arctic. We characterize the conditions and meteorological regimes that control these two different atmospheric chemistry conditions (natural vs. anthropogenic influenced) using the WRF-Chem model combined with available observations from satellite remote sensing, the Copernicus Atmosphere Modeling Service, and ERA5 reanalysis. We also focus on understanding when the cryosphere is a source of aerosols and trace gases and when it is a receptor for pollution, including particles such as dust and black carbon that can influence albedo. Finally, we discuss the two way links between atmospheric chemistry and cryospheric change, and provide recommendations for Earth system models that study these processes at longer time scales and their relationship to climatic change.
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