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

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 usually below 1 μmol m −2 h −1 because of the low HNO 3 concentration and weak turbulence over the snow surface. Some of the highest observed fluxes may be due to temporary storage by equilibrium sorption of peroxyacetylnitrate (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 bidirectional and small in magnitude, the net result of turbulent NO y exchange is insignificant compared to the 2 μmol m −2 d −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 HNO 3 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 HNO 3 by fog, falling snow, and direct deposition to the snowpack.