Diurnal and Seasonal Variations of Nitrogen Oxides within Snowpack Air and the Overlying Atmosphere at Summit, Greenland

Recent studies have shown that the transport of oxidized nitrogen species (NOx, PAN, HNO3) to the Arctic from lower latitudes can result in a deposition of nitrates to the snowpack. Subsequently, snowpack nitrate constitutes a reservoir for volatile oxidized nitrogen gases. The interstitial air of the sunlit polar snowpack is an active photochemical environment and processes initiated by summertime nitrate photolysis within the snowpack may result in an efflux of NOx which can significantly alter the oxidative capacity of the overlying atmosphere.

The extent of the impact of air-snow exchange upon tropospheric ozone has not yet been adequately assessed. This deficiency is primarily due to limited field measurements. To address this need we are currently performing the first continuous, year-round gradient measurements of nitrogen oxides and ozone both within and above the snowpack at Summit, Greenland. These measurements show that NOx levels in and above the snow exhibit a strong seasonal pattern that coincides with the incoming solar radiation cycle. During the springtime onset of photochemical activity, NOx mixing ratios in the snowpack exceeded 500 pptv at a depth of 50 cm within the snowpack.

Measurements at Summit will continue until summer 2010. Resulting data will be incorporated into a chemistry-climate model to estimate the impact of O3 and NOx exchanges within the snowpack upon the polar tropospheric O3 budget.