Denuder measurements of gas and aerosol species above Arctic snow surfaces at Alert 2000

Gas and aerosol measurements were made during the Polar Sunrise Experiment 2000 at Alert, Nunavut (Canada), using two independent denuder/filter systems for sampling and subsequent analysis by ion chromatography. Twelve to forty-eight hour samples were taken during a winter (9–21 February 2000) and a spring (17 April–5 May 2000) campaign. During the spring campaign, samples were taken at two different heights above the snow surface to investigate concentration differences. Total particulate NO3− is the most abundant inorganic nitrogen compound during Arctic springtime (mean 137.4 ng m−3). The NO3− fluxes were calculated above the snow surface to help identify processes that control snow–atmosphere exchange of reactive nitrogen compounds. We suggest that the observed fluxes of coarse particle NO3− via snow deposition may contribute to the nitrogen inventory in the snow surface. Measurements of surface snow provide experimental data that constrain the contribution of dry deposition of coarse particle NO3− to <7%. Wet deposition in falling snow appears to be the major contributor to the nitrate input to the snow.