1University of California, Los Angeles; Department of Atmospheric and Oceanic Sciences, Los Angeles, CA 90095, USA
2UPMC Université Paris 06, UMR8190, CNRS/INSU – Université Versailles St.-Quentin, LATMOS-IPSL, Paris, France
3Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH, USA
4School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK
5NOAA ATDD, 456 S. Illinois Ave, P.O. Box 2456, Oak Ridge, TN 38731, USA
6School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30033, USA
7Department of Geosciences, University of Houston, TX 77204, USA
Abstract. From 10 May through 17 June, 2007 and 6 June through 9 July, 2008 intensive sampling campaigns at Summit, Greenland confirmed that active bromine chemistry is occurring in and above the snow pack at the highest part of the Greenland ice sheet (72°36' N, 38° 25' W and 3.2 km a.s.l.). Direct measurements found BrO and soluble gas phase Br− mixing ratios in the low pptv range on many days (maxima <10 pptv). Conversion of up to 200 pg m−3 of gaseous elemental mercury (GEM) to reactive gaseous mercury (RGM) and enhanced OH relative to HO2 plus RO2 confirm that active bromine chemistry is impacting chemical cycles even at such low abundances of reactive bromine species. However, it does not appear that Bry chemistry can fully account for observed perturbations to HOx partitioning, suggesting unknown additional chemical processes may be important in this unique environment, or that our understanding of coupled NOx-HOx−Bry chemistry above sunlit polar snow is incomplete. Rapid transport from the North Atlantic marine boundary layer occasionally caused enhanced BrO at Summit (just two such events observed during the 12 weeks of sampling over the two seasons). In general observed reactive bromine was linked to activation of bromide (Br−) in, and release of reactive bromine from, the snowpack. A coupled snow-atmosphere one-dimensional model that assumed snow photochemistry as the only source successfully simulated observed NO and BrO at Summit during a three day interval when winds were weak (transport not a factor). The source of Br− in surface and near surface snow at Summit is not entirely clear, but concentrations were observed to increase when stronger vertical mixing brought free tropospheric air to the surface. Reactive Bry mixing ratios above the snow often increased in the day or two following increases in snow concentration, but this response was not consistent. On seasonal time scales concentrations of Br− in snow and reactive bromine in the air were directly related.