Overview Of Field Data on the Deposition Of Aerosol-Associated Species to the Surface Snow Of Polar Glaciers, Particularly Recent Work in Greenland

Abstract

This contribution presents a review of recent field experiments investigating the relationship between the composition of snow falling onto polar glaciers and the composition of aerosols in the overlying atmosphere. The limited data exisiting prior to the late 1980s indicated that aerosol removal processes should cause fractionation between the composition of aerosols and snow. Uncertainties regarding the relative importance of ice-nucleation scavenging, in-cloud riming of snow flakes and dry deposition over polar ice sheets precluded assessment of the impact the likely fractionation would have on efforts to reconstruct temporal variations in aerosol chemistry from ice core chemistry records. Two large international experiments on the Greenland ice sheet after 1988 focused on these, and other, issues central to understanding air-snow exchange processes. These experiments confirmed that ice-nucleation scavenging is the major process incorporating aerosol-associated species into polar snow. This process enriches snow in large aerosols relative to the aerosol population aloft. Dry deposition was found to be of minor importance at the present time, but also enriches the snow in large aerosols and the species associated with them. Since the large aerosols over Greenland are predominantly derived from sea-salt and dust, while SO4=. NH4 + and several pollutant trace metals are concentrated in submicron aerosols, snow chemistry presents a biased view of aerosol composition. However, it would appear to be possible to incorporate such a bias into efforts to reconstruct aerosol chemistry records from ice cores, were it not for several complicating factors. Spatial variability in snow chemistry will likely impose an inherent limit on the temporal resolution that will be possible in such reconstructions.