Release of NO<i>_x</i> from sunlight‐irradiated midlatitude snow

Abstract

Photochemical production and release of gas‐phase NO x (NO + NO 2 ) from the natural snowpack at a remote site in northern Michigan were investigated during the Snow Nitrogen and Oxidants in Winter study in January 1999. Snow was collected in an open 34 L chamber, which was then sealed with a transparent Teflon cover and used as an outdoor flow and reaction chamber. Significant increases in NO x mixing ratio were observed in synthetic and ambient air pulled through the sunlit chamber. [NO x ] enhancements were correlated to ultraviolet sunlight intensity, reaching ∼300 pptv under partially overcast midday, midwinter conditions. These findings are consistent with NO x production from photolysis of snowpack NO 3 − ; the observed NO x release implies production of significant amounts of OH within the snow. Snowpack NO 3 − photolysis may therefore significantly alter boundary layer levels of both NO x and oxidized compounds over wide regions of the atmosphere.