Abstract

Abstract. Concentrations and fluxes of NO_y (total reactive nitrogen), ozone concentrations and fluxes of sensible heat, water vapor and momentum were measured from May 1 to July 20, 1995 at Summit, Greenland. Median NO_y concentrations declined from 947 ppt in May to 444 ppt by July. NO_y fluxes were observed into and out of the snow, but the magnitudes were usuallly below 1 micromol m^-2h^-1 because of the low HNO₃ concentration and weak turbulence over the snow surface. Some of the highest observed fluxes may be due to temporary storage by equilibrium sorption of PAN or other organic nitrogen species on ice surfaces in the upper snowpack. Sublimation of snow at the surface or during blowing snow events is associated with efflux of NO_y from the snowpack. Because the NO_y fluxes during summer at Summit are bi-directional and small in magnitude, the net result of turbulent NO_y exchange is insignificant compared to the 2 micromol m^-2day^-1 mean input from fresh snow during the summer months. If the arctic NO_y reservoir is predominantly PAN (or compounds with similar properties) thermal dissociation of this NO_y is sufficient to support the observed flux of nitrate in fresh snow. Very low HNO₃ concentrations in the surface layer (1% of total NO_y) reflect the poor ventilation of the surface layer over the snowpack combined with the relatively rapid uptake of HNO₃ by fog, falling snow, and direct deposition to the snowpack.

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