Precipitation of salts in freezing seawater and ozone depletion events: a status report
Precipitation of salts in freezing seawater and ozone depletion events: a status report
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DOI：
10.5194/acp-8-7317-2008
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发表时间：
2008-12
影响因子：
6.3
通讯作者：
S. Morin;G. Marion;R. Glasow;Didier Voisin;J. Bouchez;J. Savarino
中科院分区：
文献类型：
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作者：
S. Morin;G. Marion;R. Glasow;Didier Voisin;J. Bouchez;J. Savarino
在春季，极地海洋边界层表现出剧烈的臭氧消耗事件（ODEs），与溴氧化物（BrO）的混合比升高。目前对这种特殊化学性质的解释需要存在酸和溴化物富集的表面，以非均匀地促进和维持ODE。Sander等人（2006年）提出，碳酸钙（CaCO3）在任何海水衍生介质中的沉淀可能会降低其碱度，使其更容易被HNO3和H2SO4等大气酸酸化。我们使用能够处理浓电解质溶液热力学的最先进的FREZCHEM模型进行模拟，试图重现他们的结果，发现当伊卡石（CaCO3·6H2O）而不是方解石（CaCO3）沉淀时，对碱度没有这种影响。鉴于最近在南极盐水中发现了伊卡石（Dieckmann等人，2008年），我们的结果表明，在使用Sander等人（2006年）的结果时应非常谨慎，并揭示了迫切需要对溴活化与表面pH值之间的实际联系进行实验室研究，溴活化应在零度以下温度下发生。此外，在冷冻过程中的盐水中的Cl/Br比的演变计算使用FREZCHEM，考虑到含Cl的盐中的Br取代。
In springtime, the polar marine boundary layer exhibits drastic ozone depletion events (ODEs), associated with elevated bromine oxide (BrO) mixing ratios. The current interpretation of this peculiar chemistry requires the existence of acid and bromide-enriched surfaces to heterogeneously promote and sustain ODEs. Sander et al. (2006) have proposed that calcium carbonate (CaCO3) precipitation in any seawater-derived medium could potentially decrease its alkalinity, making it easier for atmospheric acids such as HNO3 and H2SO4 to acidify it. We performed simulations using the state-of-the-art FREZCHEM model, capable of handling the thermodynamics of concentrated electrolyte solutions, to try to reproduce their results, and found that when ikaite (CaCO3·6H2O) rather than calcite (CaCO3) precipitates, there is no such effect on alkalinity. Given that ikaite has recently been identified in Antarctic brines (Dieckmann et al., 2008), our results show that great caution should be exercised when using the results of Sander et al. (2006), and reveal the urgent need of laboratory investigations on the actual link(s) between bromine activation and the pH of the surfaces on which it is supposed to take place at subzero temperature. In addition, the evolution of the Cl/Br ratio in the brine during freezing was computed using FREZCHEM, taking into account Br substitutions in Cl–containing salts.