The Dynamic Redox Chemistry of Metals in the Troposphere

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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.