Sea salt aerosols in polar regions: Constraining the relative roles of blowing snow and open ocean sources

Abstract:

Sea salt aerosols (SSA) have a critical influence on radiation, cloud formation and chemistry of the polar atmosphere. In addition to the commonly accepted open-ocean source of SSA, several studies have suggested that SSA can be produced by sublimation of blowing snow or frost flowers in sea-ice covered regions. To estimate and compare the role of blowing snow and open ocean sources, we implement a blowing snow SSA emission scheme for sea-ice covered regions in the GEOS-Chem global 3D chemical transport model. We analyze multi-year observations of sea salt aerosol mass concentrations at three Arctic sites (Barrow, Alaska; Alert, Canada; Zeppelin, Svalbard) and two Antarctic sites (Neumayer and Dumont d'Urville) and compare them to simulations with the GEOS-Chem model for 2001-2008. Simulations including only open-ocean SSA emissions, fails to reproduce the observed winter maximum in SSA mass concentrations at these sites. The underestimate ranges from factors of 3 to 25. Including a blowing snow SSA source leads to improved agreement with observations. Based on the comparison to surface observations, we estimate that the total SSA emissions (submicron and supermicron) from blowing snow are 2.1 Tg/yr over the Arctic and 0.6 Tg/yr over Antarctica, maximizing during winter. In contrast, for the regions poleward of 70° latitude, the open ocean source are 7 Tg/yr (Arctic) and 1 Tg/yr (Antarctic) with a maximum during late summer. We find that in the submicron range, however, SSA emissions from blowing snow play a dominant role (Arctic: 0.4 Tg/yr; Antarctic: 0.15 Tg/yr), being factors of 4-6 larger compared to emissions of submicron SSA from the open ocean (Arctic: 0.1Tg/yr ; Antarctic: 0.015Tg/yr).