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

Abstract

Abstract. Sander et al. (2006) proposed that CaCO 3 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.

Temperature dependent halogen activation by N<sub>2</sub>O<sub>5</sub> reactions on halide-doped ice surfaces

“…As temperature decreases past the freezing point of water in the halide salt solution, water ice precipitates enhancing the ionic content of the remaining brine (Lodge et al, 1956). As temperature decreases further various salt hydrates precipitate, in particular, NaCl2H 2 O and MgCl 2 12H 2 O precipitate out of the brine at temperatures of 250 and 235 K respectively (Marion and Farren, 1999;Morin et al, 2008;Richardson, 1976;Sander et al, 2006;Sander and Morin, 2010). The precipitation of chloride salts changes the relative concentration of chloride to bromide in the brine layer.…”

“…It is likely that on sea ice, snowpacks, and airborne snow particles there is a rich liquid brine layer, containing relatively high concentrations of halide and other inorganic ions, as well as organic compounds, which have been excluded from the water-ice matrix (Grannas et al, 2007;Koop et al, 2000). Moreover, the physical and chemical properties of this brine layer depend upon meteorological conditions such as temperature and relative humidity, as well as upon chemical processing and exposure to depositional sources of salts and acids (Cho et al, 2002;Koop et al, 2000;Morin et al, 2008;Sander and Morin, 2010). Experiments that probe multi-phase chemistry as a function of these parameters are generally lacking and as such the efficiency of several key reactions under typical environmental conditions remain unknown.…”

Numerical analysis of the chemical kinetic mechanisms of ozone depletion and halogen release in the polar troposphere

“…Since the 1990s, box models were used to capture the temporal evolution of the chemical species and to investigate the recycling of halogen species on the surface of aerosol or ice covered by snow (Fan and Jacob, 1992;Tang and McConnell, 1996;Sander et al, 1997;Michalowski et al, 2000). More recently, box model studies (Sander et al, 2006;Morin et al, 2008;Sander and Morin, 2010) focus on the role of calcium carbonate precipitation in the triggering of bromine explosion. The coupling of HO x , NO x and halogen chemistry is investigated by Chen et al (2007), Bloss et al (2010) and Liao et al (2011).…”

Brief Communication: Ikaite (CaCO<sub>3</sub>·6H<sub>2</sub>O) discovered in Arctic sea ice

“…Precipitation of calcium carbonate, during the formation of sea ice is considered fundamental in catalyzing chemical processes such as the boundary layer ozone depletion events (ODEs) (Sander et al, 2006;Piot and von Glasow, 2008;Morin et al, 2008;Sander and Morin, 2009), as well as the formation and subsequent draw down of CO 2 via brine drainage (Rysgaard, 2007(Rysgaard, , 2009. Furthermore, calcium carbonate found in firn off Talos Dome, Antarctica is thought to originate from sea ice and therefore could act as a proxy for sea ice cover (Sala et al, 2008).…”