Chemical composition of snowfall in the high Arctic: 1990–1994

From 1990 to 1994 at Alert, Nunavut, Canada, weekly snow samples were collected under low wind conditions to avoid contamination by blowing snow. They were analysed for major ions, Br−, and the organic ions methylsulphonate, formate, acetate and propionate. In the Arctic, where annual precipitation is low and blowing snow is common, these observations are unique. On an equivalent weight basis, acids and sea salt in snowfall are mixed approximately equally from December to January but from March to May acids dominate. The acidity of snowfall increases progressively throughout the winter to a May peak of 16 μeq l−1. SO42−, Br−, and the organic acids acetate, and propionate peak in snowfall after polar sunrise indicate the influence of enhanced photochemical reactions. The greater enrichment of halides relative to sea salt Na+ in snow compared to aerosols indicates that gaseous uptake by snowflakes is important in the removal of these substances from the atmosphere and their deposition on to the Earthʹs surface. There is a marked difference between the seasonal variation of enrichment of Cl− and Br− in snow. The latter show a marked increase after polar sunrise while the former does not. These results provide valuable baseline information on the ionic content of fresh snowfall to be used in understanding the results of snowpack chemistry and post-depositional process studies conducted in the high Arctic.