ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-9899-2011 Longpath DOAS observations of surface BrO at Summit, Greenland Stutz J. 1 Thomas J. L. 1 Hurlock S. C. 1 Schneider M. 1 von Glasow R. 2 Piot M. 3 Gorham K. 4 Burkhart J. F. 5 Ziemba L. 6 7 Dibb J. E. 6 Lefer B. L. 8 University of California, Los Angeles; Department of Atmospheric and Oceanic Sciences, Los Angeles, CA 90095, USA School of Environmental Sciences, University of East Anglia, Norwich, UK EnBW Trading, Karlsruhe, Germany University of California Irvine; School of Physical Sciences, Irvine, USA Norwegian Institute for Air Research (NILU), Kjeller, Norway Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, New Hampshire, USA NASA Langley Research Center, Hampton, VA, 23681, USA Earth and Atmospheric Sciences Department, University of Houston, Houston, TX, USA 27 09 2011 11 18 9899 9910 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/11/9899/2011/acp-11-9899-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/9899/2011/acp-11-9899-2011.pdf

Reactive halogens, and in particular bromine oxide (BrO), have frequently been observed in regions with large halide reservoirs, for example during bromine catalyzed coastal polar ozone depletion events. Much less is known about the presence and impact of reactive halogens in areas without obvious halide reservoirs, such as the polar ice sheets or continental snow. <br><br> We report the first LP-DOAS measurements of BrO at Summit research station in the center of the Greenland ice sheet at an altitude of 3200 m. BrO mixing ratios in May 2007 and June 2008 were typically between 1–3 pmol mol<sup>−1</sup>, with maxima of up to 5 pmol mol<sup>−1</sup>. These measurements unequivocally show that halogen chemistry is occurring in the remote Arctic, far from known bromine reservoirs, such as the ocean. During periods when FLEXPART retroplumes show that airmasses resided on the Greenland ice sheet for 3 or more days, BrO exhibits a clear diurnal variation, with peak mixing ratios of up to 3 pmol mol<sup>−1</sup> in the morning and at night. The diurnal cycle of BrO can be explained by a changing boundary layer height combined with photochemical formation of reactive bromine driven by solar radiation at the snow surface. The shallow stable boundary layer in the morning and night leads to an accumulation of BrO at the surface, leading to elevated BrO despite the expected smaller release from the snowpack during these times of low solar radiation. During the day when photolytic formation of reactive bromine is expected to be highest, efficient mixing into a deeper neutral boundary layer leads to lower BrO mixing ratios than during mornings and nights. <br><br> The extended period of contact with the Greenland snowpack combined with the diurnal profile of BrO, modulated by boundary layer height, suggests that photochemistry in the snow is a significant source of BrO measured at Summit during the 2008 experiment. In addition, a rapid transport event on 4 July 2008, during which marine air from the Greenland east coast was rapidly transported to Summit, led to enhanced mixing ratios of BrO and a number of marine tracers. However, rapid transport of marine air from the Greenland east coast is rare and most likely not the main source of bromide in surface snow at Summit. The observed levels of BrO are predicted to influence NO<sub>x</sub> chemistry as well as impact HO<sub>x</sub> partitioning. However, impact of local snow photochemistry on HO<sub>x</sub> is smaller than previously suggested for Summit.

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