Improving constraints on the sources and distribution of sea salt aerosols in polar regions.

摘要

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 windblown salty snow or frost flowers over sea ice-covered regions. To estimate and compare the role of sea ice and open ocean sources, we implement a blowing snow emission scheme and a frost flower emission scheme for the sea ice-covered regions in the GEOS-Chem global 3D chemical transport model. We analyze multi-year observations of SSA 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 emission fail to reproduce the observed winter maximum in SSA mass concentrations at these sites. In winter, the model underestimate ranges from factors of 3 to 25. Including a blowing snow or frost flower source of SSA leads to improved agreement with the observed seasonality. The blowing snow simulation captures the daily variability of observed SSA mass concentrations, while the frost flower simulation fails to do so. Based on the comparison to surface observations, for the regions poleward of 60° latitude, we estimate that the total annual SSA emission (submicron and supermicron) from the open ocean is 31 Tg/yr over the Arctic and 56 Tg/yr over the Antarctic, which are an order of magnitude larger than those from blowing snow or frost flowers. We find that in the submicron range, however, SSA emissions from blowing snow (1 Tg/yr over the Arctic and 2.3 Tg/yr over the Antarctic for those on all sea ice; and 0.6 Tg/yr over the Arctic and 1.9 Tg/yr over the Antarctic for those on first-year sea ice) or frost flowers (0.3 Tg/yr over the Arctic and 0.2 Tg/yr over the Antarctic) are comparable to, or even larger than, those from open ocean.