The Importance of Halogen Atom Chemistry in the Arctic Troposphere

9631572 谢普森 最近在北极的观测表明，在北冰洋表面附近的对流层低层中发生了一个臭氧迅速被破坏的过程，人们对此知之甚少。一些实地测量研究得出了臭氧被溴原子催化循环破坏的假设。如果这在一般海洋环境中是重要的，那么它将对我们理解和模拟对流层臭氧的全球收支产生重大影响。然而，有几个领域的化学和动力学的过程是知之甚少，例如：什么是溴原子的来源？产生的BrO自由基的命运如何？活性溴自由基的重要去除机制是什么？HBr的回收机制是什么？北极对流层臭氧破坏的空间和时间特征是什么？普渡大学汇集了四组具有互补能力的研究人员，使他们能够独特地寻求这些问题的答案。这项研究工作的具体目标和相关方法是： (1)在与北极有关的条件下，测量操作反应的动力学，这些反应可能发生在海盐或酸性硫酸盐气溶胶的表面或内部，溴离子在这些反应中被氧化成分子溴或其他光解活性溴化合物。这些测量将使用停流和脉冲加速流光谱技术进行。 (2)研究了溴、氯原子与醛、酮反应的竞争反应途径、溴氧自由基与氯氧自由基的反应以及阴离子在溴离子水相氧化反应中的催化作用。这项工作将使用从头计算方法进行。 (3)高灵敏度和高选择性方法的开发和应用 羰基化合物的测定。该仪器将在今后的油田开发中得到应用 北极的项目。实验室、实地和计算研究的结果将纳入北极海洋边界层详细化学情况的箱型模型。 (4)普渡大学的中尺度模型将加以改进，以应用于北极。 然后，将根据北极的观测数据对修改和优化的模型进行测试，然后纳入箱型模型化学。 ***

9631572 Shepson Recent observations in the Arctic indicate that there is a poorly understood process occurring in which ozone is rapidly destroyed in the lower troposphere near the surface of the Arctic Ocean. A number of field measurement studies have resulted in the hypothesis that ozone is being destroyed by a catalytic cycle involving Br atoms. If this were important in the marine environments in general, it would have substantial implications for our understanding and modeling of the global budget of tropospheric ozone. However, there are several areas of the chemistry and dynamics of the process that are poorly understood, for example: What is the source of bromine atoms? What is the fate of the BrO radicals produced? What are the important removal mechanisms for reactive bromine radicals? What is the mechanism for recycling HBr? What are the spatial and temporal characteristics of ozone destruction in the Arctic troposphere? Purdue University has brought together four groups of researchers with complementary capabilities to enable them to uniquely pursue the answers to these questions. The specific objectives, and associated approaches, of this research effort are: (1) Measurement of the kinetics of the operative reactions, presumably occurring on the surface of or within sea salt or acidic sulfate aerosol, whereby bromide ions are oxidized to molecular bromine or other photolytically active bromine compounds, under conditions relevant to the Arctic. These measurements will be conducted using stopped-flow and pulsed accelerated flow spectroscopic techniques. (2) Investigation of the competitive reaction paths for Br and Cl atom reactions with aldehydes and ketones, the reactions between BrO and ClO radicals, and the role of anions in catalyzing aqueous phase oxidation of the bromide ion. This work will be conducted using ab initio computational methods. (3) Development and application of highly sensitive and selective methods for the mea surement of carbonyl compounds. This instrument will be used in future field projects in the Arctic. The results of the laboratory, field and computational studies will be integrated into a box model of the detailed chemistry occurring in the Arctic marine boundary layer. (4) The Purdue Mesoscale Model will be refined for application to the Arctic. The modified and optimized model will then be tested against observational data from the Arctic, followed by incorporation of the box-model chemistry. ***