Evidence of NO_<i>x</i> production within or upon ice particles in the Greenland snowpack

Abstract

NO x and NO y were determined in the interstitial air of surface snow and in ambient air at Summit, Greenland. NO x levels in interstitial air were 3 to &gt;10 times those in ambient air, and were generally greater than ambient NO y 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 NO x from a N‐reservoir compound within the snow. Average [NO x ]:[HNO 3 ] and [NO x ]:[NO y ] ratios in ambient air above the snow were elevated relative to other remote sites, indicating that NO x release within the snowpack may have altered NO x levels in the overlying atmospheric boundary layer. We suggest that the observed release of NO x 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.