Iron is found at variable levels in the atmosphere in both aqueous-phases and solid phases. Ferric iron has been shown to be an important catalyst for the autoxidation of SO2 and concomitant generation of acidity in clouds and fogs. Recent field research has provided strong evidence that Fe derived from atmospheric deposition is a limiting growth nutrient for various species of phytoplankton in some regions of the open ocean. Thus the atmospheric deposition of iron in various forms (i.e. redox states and species) could be a critical factor in controlling oceanic phytoplankton production which in turn may affect atmospheric CO2 levels. The PIs propose to investigate the detailed chemical speciation of iron in atmospheric water droplets and in aerosol samples collected from a variety of locations representative of urban, rural and remote atmospheres. They plan to determine the various solid-phase and aqueous-phase chemical forms and oxidation states (speciation) of iron present in cloud-, fog- and rainwater collected from marine and continental environments and to interpret the experimental observations within the framework of coupled thermodynamic and kinetic models.
