Climate-relevant natural wind-driven aerosol processes in the Arctic

Aerosols influence Earth's climate through direct interactions with radiation and by modifying cloud properties via their effects on cloud droplet and ice crystal formation. Uncertainties associated with aerosol-radiation and aerosol-cloud interactions represent the largest physical uncertainty in quantifying climate change, arising from the complexity of aerosol processes, limited observations, poor constraints on pre-industrial aerosol, and incomplete representation of aerosol processes in climate models. These uncertainties are particularly relevant in the Arctic, where climate change is amplified and aerosol-cloud and aerosol-radiation interactions play a key role in the surface energy balance. This thesis focuses on two natural aerosol sources in the Arctic, sea salt aerosol associated with blowing snow and mineral dust from high-latitude glacial outwash plains, with the aim of characterizing their climate-relevant properties. Both aerosol sources can exert strong climate impacts as ice-nucleating particles (INPs), cloud condensation nuclei (CCN), or contributors to scattering, yet remain poorly constrained by Arctic observations. Comprehensive observations from the year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition (2019-2020) were used to examine wind-driven aerosol production in the central Arctic. Periods of high wind speed and blowing snow were associated with strong enhancements in aerosol number concentrations, submicron sodium chloride mass, CCN concentrations, and scattering coefficients, indicating the potential climate relevance of this process. Seasonal differences and the influence of snow age on aerosol enhancements highlight the dependence on season and surface conditions. Accounting for air mass history demonstrates the role of regional transport in explaining coarse-mode aerosol variability. Together, these results provide direct observational evidence for wind-driven aerosol production in the central Arctic and offer constraints for model evaluation. Glacier retreat across the Arctic exposes new land surfaces and leads to the expansion of glacial outwash plains rich in fine glacial dust, which can influence cloud properties upon emission. To investigate high-latitude dust as an INP source, a two-month field campaign was conducted in southwestern Greenland in 2023. To support these measurements, the Sion Particle Ice Crystallization Experiment (SPICE), a droplet freezing assay for measuring immersion-mode INPs, was developed and validated in the laboratory. Glacial dust in southern Greenland showed ice nucleating activity relevant for mixed-phase clouds, but with lower activity compared to other high-latitude dust sites, highlighting variability in the Arctic. Small amounts of organic material were identified as the main driver of ice-nucleating activity and its variability in the glacial outwash plains. Atmospheric INP measurements indicated a