Measurements of readily soluble Fe(II) and Fe(III) in aerosols were made during cruises in the Atlantic and in the Pacific regions. A large fraction of the soluble aerosol Fe was found to be Fe(II), about 50 percent on average, suggesting active photochemical redox cycling in aqueous coating which must be present on insoluble Fe-containing particles. In this study, we simulate the aerosol Fe speciation using a model of the redox chemistry based on reported kinetics and mechanism. In the model, concentrations of HO2 and dissolved Cu/Fe ratio are factors influencing the Fe(II) and Fe(III) partitioning. Gas-phase HO2, rather than photolysis of ferric hydroxide ions, is the main driver of diurnal variation in dissolved Fe speciation. Fe(II) measured at night implies continued redox cycling, and thus HO2 production, in the dark. Reduction of Fe(III) to Fe(II) enhances aerosol Fe solubility and atmospheric deposition of bioavailable Fe to the ocean.

Measurement and modeling of aerosol Fe speciation

244th National Meeting (2012)

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