Release of NO(x) from sunlight-irradiated midlatitude snow

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Photochemical production and release of gas-phase NO(x) (NO + NO < inf> 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, mid-winter conditions. These findings are consistent with NO(x) production from photolysis of snowpack NO < inf> 3 < sup> - ; the observed NO(x) release implies production of significant amounts of OH within the snow. Snowpack NO < inf> 3 < sup> - photolysis may therefore significantly alter boundary layer levels of both NO(x) and oxidized compounds over wide regions of the atmosphere.

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Geophysical Research Letters