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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 13, issue 19 | Copyright
Atmos. Chem. Phys., 13, 9789-9800, 2013
https://doi.org/10.5194/acp-13-9789-2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 07 Oct 2013

Research article | 07 Oct 2013

Photochemical chlorine and bromine activation from artificial saline snow

S. N. Wren, D. J. Donaldson, and J. P. D. Abbatt S. N. Wren et al.
  • Department of Chemistry, University of Toronto, 80 St. George St., Toronto, ON M5S 3H6, Canada

Abstract. The activation of reactive halogen species – particularly Cl2 – from sea ice and snow surfaces is not well understood. In this study, we used a photochemical snow reactor coupled to a chemical ionization mass spectrometer to investigate the production of Br2, BrCl and Cl2 from NaCl/NaBr-doped artificial snow samples. At temperatures above the NaCl-water eutectic, illumination of samples (λ > 310 nm) in the presence of gas phase O3 led to the accelerated release of Br2, BrCl and the release of Cl2 in a process that was significantly enhanced by acidity, high surface area and additional gas phase Br2. Cl2 production was only observed when both light and ozone were present. The total halogen release depended on [ozone] and pre-freezing [NaCl]. Our observations support a "halogen explosion" mechanism occurring within the snowpack, which is initiated by heterogeneous oxidation and propagated by Br2 or BrCl photolysis and by recycling of HOBr and HOCl into the snowpack. Our study implicates this important role of active chemistry occurring within the interstitial air of aged (i.e. acidic) snow for halogen activation at polar sunrise.

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