ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-7655-2010 Introducing the bromide/alkalinity ratio for a follow-up discussion on "Precipitation of salts in freezing seawater and ozone depletion events: a status report", by Morin et al., published in Atmos. Chem. Phys., 8, 7317–7324, 2008 Sander R. 1 Morin S. 2 3 Air Chemistry Department, Max-Planck Institute of Chemistry, P.O. Box 3060, 55020 Mainz, Germany Météo-France – CNRS, CNRM/GAME, CEN, 1441, rue de la piscine, 38400 St. Martin d'Hères, France CNRS – UJF Grenoble, LGGE, 54 rue Molière, 38400 St Martin d'Hères, France 17 08 2010 10 16 7655 7658 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/10/7655/2010/acp-10-7655-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/7655/2010/acp-10-7655-2010.pdf

Sander et al. (2006) proposed that CaCO<sub>3</sub> precipitation can be an important factor in triggering tropospheric ozone depletion events. Recently, Morin et al. (2008b) presented calculations with the FREZCHEM model and concluded that their results and interpretation cast doubt on the validity of this hypothesis. In this joint publication, we have re-analyzed the implications of the FREZCHEM results and show how they can be reconciled with the proposal of Sander et al. (2006). The chemical predictions of both approaches are consistent. Although an interpretation solely based on the alkalinity change in the brine does not support the conclusion of Sander et al. (2006), we show that the bromide/alkalinity ratio (which increases during the cooling of the brine) can be used as an indicator of the potential for triggering bromine explosions.

 References Dieckmann, G S., Nehrke, G., Papadimitriou, S., Göttlicher, J., Steininger, R., Kennedy, H., Wolf-Gladrow, D., and Thomas, D N.: Calcium carbonate as ikaite crystals in Antarctic sea ice, Geophys. Res. Lett., 35, L08501, \doi10.1029/2008GL033540, 2008. Dieckmann, G. S., Nehrke, G., Uhlig, C., Göttlicher, J., Gerland, S., Granskog, M. A., and Thomas, D. N.: Brief Communication: Ikaite (CaCO<sub>3</sub>·6H<sub>2</sub>O) discovered in Arctic sea ice, The Cryosphere, 4, 227–230, doi:10.5194/tc-4-227-2010, 2010. Koop, T., Kapilashrami, A., Molina, L T., and Molina, M J.: Phase transitions of sea-salt/water mixtures at low temperatures: Implications for ozone chemistry in the polar marine boundary layer, J. Geophys. Res., 105D, 26393–26402, 2000. Marion, G M.: Carbonate mineral solubility at low temperatures in the \chemNa-\chemK-\chemMg-\chemCa-\chemH-\chemCl-\chemSO_4-\chem% OH-\chemHCO_3-\chemCO_3-\chemCO_2-\chemH_2O system, Geochim. Cosmochim. Acta, 65, 1883–1896, 2001. Marion, G. M., Millero, F. J., and Feistel, R.: Precipitation of solid phase calcium carbonates and their effect on application of seawater $S_A−T−P$ models, Ocean Sci., 5, 285–291, doi:10.5194/os-5-285-2009, 2009. Morin, S., Marion, G. M., von Glasow, R., Voisin, D., Bouchez, J., and Savarino, J.: Precipitation of salts in freezing seawater and ozone depletion events: a status report, Atmos. Chem. Phys. Discuss., 8, 9035–9060, doi:10.5194/acpd-8-9035-2008, 2008a. Morin, S., Marion, G. M., von Glasow, R., Voisin, D., Bouchez, J., and Savarino, J.: Precipitation of salts in freezing seawater and ozone depletion events: a status report, Atmos. Chem. Phys., 8, 7317–7324, doi:10.5194/acp-8-7317-2008, 2008b. Sander, R., Burrows, J., and Kaleschke, L.: Carbonate precipitation in brine – a potential trigger for tropospheric ozone depletion events, Atmos. Chem. Phys., 6, 4653–4658, doi:10.5194/acp-6-4653-2006, 2006. Tang, I N., Tridico, A C., and Fung, K H.: Thermodynamic and optical properties of sea salt aerosols, J. Geophys. Res., 102D, 23269–23275, 1997. Treffeisen, R., Krejci, R., Ström, J., Engvall, A. C., Herber, A., and Thomason, L.: Humidity observations in the Arctic troposphere over Ny-Ålesund, Svalbard based on 15 years of radiosonde data, Atmos. Chem. Phys., 7, 2721–2732, doi:10.5194/acp-7-2721-2007, 2007.