The Dynamic Redox Chemistry of Metals in the Troposphere

9303024霍夫曼根据加州理工学院目前的研究，已经确定近岸大陆对流层中铁的氧化还原循环既包括溶解的表面物种，也包括气溶胶表面的物种，主要受可氧化有机化合物的水平控制，这些可氧化有机化合物与含有Fe(III)的各种相和物种共存。这些共存的有机化合物通过Fe(III)物种(可溶的络合物和金属氧化物晶型)进行热氧化和光助氧化生成羧酸。这种化学相互依存性与观察到的海洋层状云中Fe(II)和CH3二氧化碳浓度之间的强烈相关性是一致的。此外，研究表明，当有草酸盐和甲酸盐等电子给体存在时，照射后的环境气溶胶颗粒会产生相对较大浓度的过氧化氢。这些结果表明，照亮的云层和雾霾气溶胶可能为对流层中的气团提供了一种原位的过氧化氢来源。关于大气中氧化能力的来源，这一结果是对全球对流层化学具有重要意义的重大发现。根据正在进行的大气中铁的动态化学研究(NSF Grant ATM-9015775)，已经确定了以下研究目标：1)通过实验确定从海洋和大陆(农村和城市)环境中收集的云、雾和雨水中铁的各种化学形态和氧化状态；2)表征参与大气水滴中氧化还原循环的铁和锰的固相，并追踪其来源至大气。

9303024 Hoffmann Based on current research a Caltech, it has been determined that the redox cycle of Fe in near-shore continental troposphere involves both dissolved and aerosol surface species and it is controlled primarily by level of oxidizable organic compounds that co-exist with the various phases and species containing Fe(III). These co-existing organic compounds undergo thermal and photo- assisted oxidation by Fe(III) species (soluble complexes and metal oxide polymorphs) to yield carboxylic acids. This chemical interdependency is consistent with the strong correlation observed between the concentrations of Fe(II) and CH3 carbon dioxide in marine stratus clouds. In addition, irradiated ambient aerosol particles have been shown to produce relatively large concentrations of h2o2 when electron donors such as oxalate and formate are present. These results suggest that illuminated clouds and haze aerosol may provide an in situ source of hydrogen peroxide to air parcels in the troposphere. This result is a major finding of significance to global troposphere chemistry in regards to sources of oxidizing capacity in the atmosphere. In light of the on-going research (NSF Grant ATM-9015775 on the dynamic chemistry of iron in the atmosphere, the following research objectives have been established: 1) experimentally determine the various chemical forms and oxidation states of Fe in cloud-, fog- and rainwater collected from marine and continental (both rural and urban) environments, 2) characterize the solid- phase of Fe and Mn, which participate in redox cycles in atmospheric water droplets, and trace their sources to the atmosphere.