Impacts of Sea Ice Leads on Sea Salt Aerosols and Atmospheric Chemistry in the Arctic

Abstract. Sea salt aerosols (SSA) alter Arctic climate through interactions with radiation and clouds. The processes contributing to Arctic cold season (November–April) SSA remain uncertain. Observations from coastal Alaska suggest emissions from open leads in sea ice, which are not included in climate models, may play a dominant role. Their Arctic-wide significance has not yet been quantified. Here, we combine satellite data of lead area (the AMSR-E product) and a chemical transport model (GEOS-Chem) to quantify pan-Arctic SSA emissions from leads during the cold season from 2002–2008 and predict their impacts on atmospheric chemistry. Lead emissions vary seasonally and interannually. Total monthly SSA emissions increase by 1.0–1.8 % (≥60° N latitude) and 5.8–8.4 % (≥75° N). The AMSR-E product detects at least 50 % of total lead area as compared to optical MODIS satellite images. SSA concentrations increase primarily at the location of leads, where standard model concentrations are low. GEOS-Chem overestimates SSA concentrations at Arctic sites even when lead emissions are not included, suggesting underestimation of SSA sinks and/or uncertainties in SSA emissions from blowing snow and open leads. Multi-year monthly mean surface bromine atom (Br) concentrations increase 2.8–8.8 % due to SSAs from leads. Changes in ozone concentrations are negligible. While leads contribute <10 % to Arctic-wide SSA emissions in the years 2002–2008, these emissions occur in regions of low background aerosol concentrations. Leads are also expected to increase in frequency under future climate change. Thus, lead SSA emissions could have significant impacts on Arctic climate.