Atmospheric particle abundance and sea salt aerosol observations in the springtime Arctic: a focus on blowing snow and leads

Abstract. 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 that Arctic sea ice leads are 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 (3 April–7 May 2016). Blowing snow conditions were observed during 25 % of the 5-week study period and
were overpredicted 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 6, 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
sublimated would 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.
