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

NOs and NOv were determined in the interstitial air of surface snow and in ambient air at Summit, Greenland. NOs levels in interstitial air were 3 to > 10 times those in ambient air, and were generally greater than ambient NOy levels. [NO y] 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 NOs from a N-reservoir compound within the snow. Average [NO•]:[HNO3] and [NO•]:[NOy] ratios in ambient air above the snow were elevated relative to other remote sites, indicating that NOs release within the snowpack may have altered NOs levels in the overlying atmospheric boundary layer. We suggest that the observed release of NOx may have been initiated by photolysis of nitrate, present in relative abundance in surface snow at Summit. Such a process may affect levels of nitrate and other compounds in surface snow, the overlying atmosphere, and glacial ice, and its potential role in cirrus cloud chemistry should be investigated.