Snow-atmosphere interactions in Arctic snowpacks -- net fluxes of NO3, SO4 and influence of solar radiation

Identical experiments on snow-atmosphere interaction were carried out at two arctic sites (open forest and tundra, Inuvik, Canada) prior to spring snowmelt, April 1992. The purpose of the experiments was to estimate the magnitude and direction of net fluxes (dry deposition/re-emission) of NO3 and SO4 between the snow surface and the atmosphere from changes in concentrations of these species in the surface snow over periods of 36-48 hours. The experiment was also designed to determine the influence of solar radiation on fluxes of NO3 and SO4. The methodology included a procedure to homogenize surface snow; this served to normalize the initial chemical conditions for all sample sets used in the experiment. The homogeneous samples were exposed to the atmosphere in a series of mesh bags which allowed free exchange of water vapour, trace gases and aerosols between the atmosphere and the snow. The control study for the influence of solar radiation on the snow-atmosphere exchange was identical to that of the bagged snow under open sunny sky except that it was carried out in the shade of an opaque fly sheet. The chemical composition and snow-water equivalent (SWE) of all bagged snows were determined before and after each experiment. The results from experiments at both sites show that solar radiation had no influence on show-atmosphere exchange of NO3 and SO4. In the first experiment at the forested site sublimation of water vapour from the snow occurred. The mass loss of water vapour was equally offset in sun and shade by significant increases in NO3 concentrations and no net loss or gain of this species by snow-atmosphere exchange thus took place. Changes in the concentrations of SO4 were not significant indicating that no dry deposition of this species had occurred. In the second experiment at the tundra site there was no loss of mass by sublimation. However in this case a significant net exchange of SO4 from the atmosphere to the snow with a dry deposition velocity of 0.09 cm/s was measured.