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pH-dependent production of molecular chlorine, bromine, and iodine from frozen saline surfaces

机译：来自冷冻盐水表面的pH依赖性生产的分子氯，溴和碘

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The mechanisms of molecular halogen production from frozen saline surfaces remain incompletely understood, limiting our ability to predict atmospheric oxidation and composition in polar regions.In this laboratory study, condensed-phase hydroxyl radicals (OH) were photochemically generated in frozen saltwater solutions that mimicked the ionic composition of ocean water.These hydroxyl radicals were found to oxidize Cl~-, Br~-, and I~-, leading to the release of Cl_2, Br_2, I~2, and IBr.At moderately acidic pH (buffered between 4.5 and 4.8), irradiation of ice containing OH precursors (either of hydrogen peroxide or nitrite ion) produced elevated amounts of I~2.Subsequent addition of O3 produced additional I~2, as well as small amounts of Br_2.At lower pH (1.7–2.2) and in the presence of an OH precursor, rapid dark conversion of I~-to I~2 occurred from reactions with hydrogen peroxide or nitrite, followed by substantial photochemical production of Br_2 upon irradiation.Exposure to O_3 under these low pH conditions also increased production of Br_2 and I~2; this likely results from direct O_3 reactions with halides, as well as the production of gas-phase HOBr and HOI that subsequently diffuse to frozen solution to react with Br~-and I~-.Photochemical production of Cl_2 was only observed when the irradiated sample was composed of highpurity NaCl and hydrogen peroxide (acting as the OH precursor) at pHD1.8.Though condensed-phase OH was shown to produce Cl_2 in this study, kinetics calculations suggest that heterogeneous recycling chemistry may be equally or more important for Cl_2 production in the Arctic atmosphere.The condensed-phase OH-mediated halogen production mechanisms demonstrated here are consistent with those proposed from recent Arctic field observations of molecular halogen production from snowpacks.These reactions, even if slow, may be important for providing seed halogens to the Arctic atmosphere.Our results suggest the observed molecular halogen products
机译：来自冷冻盐水表面的分子卤素产生的机制仍然不完全理解，限制了我们预测极性地区的大气氧化和组合物的能力。在该实验室研究中，冷冻相羟基自由基（OH）在模仿的冷冻盐水溶液中显影。海洋水的离子组成。发现这些羟基自由基氧化Cl〜 - ，Br〜 - ，以及I〜 - ，导致Cl_2，Br_2，I〜2和IBr.at中等酸性pH（4.5之间的缓冲） 4.8），含有OH前体的冰（过氧化氢或亚硝酸盐离子的冰）的照射产生升高量的I〜2.在其它I〜2中产生的O 3加入O 3，以及少量BR_2.AT较低的pH（1.7 -2.2）并且在OH前体的存在下，I〜-TO I〜2的快速暗转化从过氧化氢或亚硝酸盐的反应发生，然后在照射时进行大量的光化学生产。曝光至O_3 und ER这些低pH条件也增加了BR_2和I〜2的产生;这可能来自直接O_3与卤化物的反应，以及随后扩散到冷冻溶液的气相HOBR和HOI的产生，以与BR〜-10〜-.当辐照样品时才观察到CL_2的光学产生。在PHD1.8中由高硫化NaCl和过氧化氢（用作OH前体）组成。虽然在本研究中显示缩合相OH产生CL_2，但动力学计算表明，异构回收化学对CL_2生产可能同样重要或更重要在北冰气氛中。这里证明的冷凝相OH介导的卤素产生机制与来自雪堆的分子卤素产生的最近北极场观测所提出的那些符合。这些反应，即使缓慢，对于向该种子卤素提供种子可能是重要的北极气氛。我们的结果表明观察到的分子卤素产品

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