Evidence of NOx production within or upon ice particles in the Greenland snowpack

NOx and NOy were determined in the interstitial air of surface snow and in ambient air at Summit, Greenland. NOx levels in interstitial air were 3 to >10 times those in ambient air, and were generally greater than ambient NOy levels. [NOy] in interstitial air varied diurnally in a manner consistent with photochemical generation within the snowpack. These observations imply that photochemical reactions occurring within or upon the ice crystals of surface snow produced NOx from a N-reservoir compound within the snow. Aver age [NOx]:[HNO3] and [NOx]:[NOy] ratios in ambient air above the snow were elevated relative to other remote sites, indicating that NOx release within the snowpack may have altered NOx levels in the overlying atmospheric boun dary layer. We suggest that the observed release of NOx may have been initi ated by photolysis of nitrate, present in relative abundance in surface sno w at Summit. Such a process may affect levels of nitrate and other compound s in surface snow, the overlying atmosphere, and glacial ice, and its poten tial role in cirrus cloud chemistry should be investigated.