Concentrations and snow-atmosphere fluxes of reactive nitrogen at Summit, Greenland

Concentrations and fluxes of NOy. (total reactive nitrogen), ozone concentr ations and fluxes of sensible heat, water vapor, and momentum were measured from May 1 to July 20, 1995 at Summit, Greenland, Median NOy, concentratio ns declined from 947 ppt in May to 444 ppt by July. NOy. fluxes were observ ed into and out of the snow, but the magnitudes were usually below 1 mu mol m(-2) h(-1) because of the low HNO3 concentration and weak turbulence over the snow surface. Some of the highest observed fluxes may be due to tempor ary storage by equilibrium sorption of peroxyacetylnitrate (PAN) or other o rganic nitrogen species on ice surfaces in the upper snowpack, Sublimation of snow at the surface or during blowing snow events is associated with eff lux of NOy from the snowpack. Because the NOy fluxes during summer at Summi t are bidirectional and small in magnitude, the net result of turbulent NOy . exchange is insignificant compared to the 2 mu mol m(-2) d(-1) mean input from fresh snow during the summer months. If the arctic NOy, reservoir is predominantly PAN (or compounds with similar properties), thermal dissociat ion of this NOy, is sufficient to support the observed flux of nitrate in f resh snow. Very low HNO3 concentrations in the surface layer (1% of total N Oy) reflect the poor ventilation of the surface layer over the snowpack com bined with the relatively rapid uptake of HNO3 by fog, falling snow, and di rect deposition to the snowpack.