Processes and properties of snow-air transfer in the high Arctic with application to interstitial ozone at Alert, Canada

Recent measurements of reactive chemical species in snow and firn at polar sites have served to underscore the importance of air snow transfer processes in understanding changes in atmospheric chemistry. In this paper we present the first quantitative assessment of the impact of physical processes in the snow on air snow chemical exchange of ozone. Measurements of snow properties, interstitial ozone concentrations, and an ozone kinetic depletion experiment results are presented along with two-dimensional model results of the diffusion and ventilation processes affecting gas exchange at Alert, Nunavut, Canada. The Arctic snowpack at Alert will allow rapid exchange of gases with the atmosphere. Even under natural ventilation conditions with moderate winds, the entire pack is exposed to air movement and therefore available for chemical exchange processes. Both measurements and model results indicate that ozone undergoes rapid depletion in the top centimeters of the snow-approximately within the top 5 cm under diffusion alone, and in the top 10 cm or less during ventilation. Due to the higher permeability of the snowpack on the sea ice site as compared to the terrestrial site, it is possible that chemical exchange processes could be even more rapid over the sea ice in the greater Arctic than at the terrestrial site. A quantitative discussion of complications that arise from current firn air sampling techniques is presented and possible improvements for future measurements are suggested. (C) 2002 Elsevier Science Ltd. All rights reserved.