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Sea salt aerosols play an important role in the radiation budget and atmospheric composition over the Arctic, where the climate is rapidly changing. Previous observational studies have shown Arctic sea ice leads to be an important source of sea salt aerosols, and modeling efforts have also proposed blowing snow sublimation as a source. In this study, size-resolved atmospheric particle number concentrations and chemical composition were measured at the Arctic coastal tundra site of Utqiaġvik, Alaska during spring (April 3 – May 7, 2016). Blowing snow conditions were observed during 25 % of the five-week study period and were over-predicted by a commonly used blowing snow parameterization based solely on wind speed and temperature. Throughout the study, open leads were present locally. During periods when blowing snow was observed, significant increases in the number concentrations of 0.01–0.06 μm particles (factor of six, on average) and 0.06–0.3 μm particles (67 %, on average), and a significant decrease (82 %, on average) in 1–4 μm particles, were observed, compared to low wind speed periods. These size distribution changes were likely caused by the generation of ultrafine particles from leads and/or blowing snow, with scavenging of supermicron particles by blowing snow. At elevated wind speeds, both submicron and supermicron sodium and chloride mass concentrations were enhanced, consistent with wind-dependent local sea salt aerosol production. At moderate wind speeds below the threshold for blowing snow, as well as during observed blowing snow, individual sea spray aerosol particles were measured. These individual salt particles were enriched in calcium relative to sodium in seawater, due to the binding of this divalent cation with organic matter in the sea surface microlayer and subsequent enrichment during seawater bubble bursting. The chemical composition of the surface snowpack also showed contributions from sea spray aerosol deposition. Overall, these results show the contribution of sea spray aerosol production from leads on both aerosols and the surface snowpack. Therefore, if blowing snow sublimation contributed to the observed sea salt aerosol, the snow being sublimed must have been impacted by sea spray aerosol deposition, rather than upward brine migration through the snowpack. Sea spray aerosol production from leads is expected to increase, with thinning and fracturing of sea ice in the rapidly warming Arctic.

International audience; The Arctic is influenced by long-range transport of aerosols from mid-latitude emissions, especially in winter and spring, leading to formation of Arctic Haze. Natural aerosols, such as sea-salt, also contribute to wintertime Arctic aerosol loadings. Local sources of aerosols are highlighted as being important, but many uncertainties remain about the relative contributions of natural and anthropogenic sources and aerosol processes. In particular, models have difficulties reproducing observed aerosol distributions and composition.In this study, the Weather Research Forecasting Model with chemistry (WRF-Chem) is used to investigate origins of wintertime aerosols over northern Alaska focusing on the influence of local versus remote sources and examining the role of meteorology, in particular, stable boundary layers that can trap aerosols near the surface. The model was run first in hemispheric mode using AMAP-ECLIPSEv6 anthropogenic emissions and a dynamical (WRF) setup for improved simulation of cold, stable meteorological conditions over wintertime Alaska. Model results are evaluated against available surface data and, in particular, data collected at Utqiaġvik during January-February 2014. A variety of air masses were sampled including air masses originating from the Arctic Ocean and from the North Slope of Alaska oil and gas extraction emissions to the east on the northern coast of Alaska.We investigate the ability of the model to reproduce observed natural aerosols, especially local and transported sea-salt and marine organic aerosols. The sensitivity of modelled aerosols and natural emissions to, for example, sea-ice fraction, surface winds, and relative humidity, are examined, as well as model treatments of marine organic aerosols. We also investigate the ability of the model to reproduce anthropogenic aerosols originating from remote sources and runs including local emissions are used to assess the influence of aerosols originating from the North Slope of Alaska oil fields. Simulations at higher resolutions over northern Alaska are also used to examine the effect of increasing model resolution on simulated meteorology and boundary layer aerosols. The results are used to estimate the relative contributions of local and remote natural and anthropogenic aerosols to wintertime aerosols over northern Alaska.