SNOSP: Ion deposition and concentration in high alpine snow packs

The present paper summarizes the results of SNOSP, a snow sampling program carried out in the Alps in the years from 1991 to 1993 in order to study the chemical composition of the high alpine snow pack. The paper briefly describes the sampling sites and the procedures used, focussing then on the geographical, seasonal and year to year variation of the mean concentration and total deposition of eight major ions, viz., chloride, nitrate, sulfate, ammonium, sodium, potassium, magnesium and calcium. NH⁺ ₄, NO^- ₃ and SO⁼ ₄concentrations in spring snow are higher by a factor of two to three than in winter snow since the lower tropospheric convection is confined to the valleys in winter and extends beyond glacier altitudes in spring. This underlines the importance of local and regional versus long range transport of contamination to the high elevated sites. The Ca⁺⁺ deposition occurs in single events (e.g., dust input from the Sahara) with a slightly higher incidence in spring that is consistent with the annual course of atmospheric circulation patterns. Most ionic species display a west to east increase of concentration by about one third. The prevailing precipitation patterns have opposite gradients so that total ionic load of the respective snowpack has no regional preference. The seasonal contrast as expressed by ratios of spring to winter concentrations of NH⁺ ₄, NO^- ₃ and SO⁼ ₄ is stronger in the west than in the east, and the east to west contrast is greater in winter than in spring.