THE COMPOSITION OF RIME ICE AS AN INDICATOR OF THE QUALITY OF WINTER DEPOSITION

Rime ice deposition and snow chemistry has been determined over a 4-ye ar period on the summit of Cairngorm Mountain, NE Scotland. The direct ion of ice deposition reflected the dominant air mass movement over th e summit. Sea salt concentrations in the rime ice were approximately 2 .5 times greater than in snow deposited over the same period. Excess s ulphate concentrations were double, and those of nitrate nearly four t imes higher. The direction of deposition influenced concentrations of excess sulphate and nitrogen species (nitrate and ammonium) in rime ic e. The same directional effect was found in the snow chemistry indicat ing increased entrapment of pollutants, or a more polluted air mass, w hen it prevailed from a Southerly or Easterly direction. The potential surface reactions involving gaseous species of S and N may increase t he ionic loading to the rime and reflect natural ionic enrichment of t he rimed snowpack surface. Because of such phenomena, rime ice is prop osed as a further indicator of winter air quality revealing important information on ionic interactions and total deposition flux measuremen t, especially at high altitudes.