The hydrolysis of iron(III) ions in aqueous solution forms a series of soluble hydroxide complexes with associated equilibrium constants. The solubility of iron(III) is controlled by the various soluble hydroxide complexes, and can, in theory, be calculated from the pH and equilibrium constants. Experimental verification of the calculated solubility has proven difficult due to the lack of sensitive analytical techniques and the presence of colloidal ferric hydroxide interferences. Recently, electrochemical methods for the determination of low levels of iron(III) have been developed using adsorptive cathodic stripping voltammetry which relies on the interfacial accumulation of the chelate of iron with Solochrome Violet RS on a hanging mercury drop electrode. The purpose of this investigation was to experimentally verify the calculated solubility of iron(III) in the pH 4-12 region using adsorptive cathodic stripping voltammetry. The ubiquitous nature of iron requires background levels of iron be reduced below the experimental concentrations to be determined. Attempts to lower the background levels of iron were ineffective as concentrations below about 10-8M iron could not be attained. Verification of the calculated solubility of iron(III) was unsuccessful as background concentrations of iron(III) and tr.e presence of colloidal ferric hydroxide hindered the experimental results. The dissolution of the ferric hydroxide colloids coupled with the background levels of iron resulted in the determination of experimental concentrations which exceeded theoretical values by two to four orders of magnitude.

abstract: Particulate trace metals can enter the atmosphere as mineral dust, sea spray, anthropogenic emissions, biomass burning, etc. Once in the atmosphere they can undergo a variety of transformations including aqueous phase (cloud) processing, photochemical reactions, interact with gases, and ultimately deposit. Metals in aerosols are of particular interest because of their natural and anthropogenic sources as well as their effects on local (human health) and global (climate change) scales. This work investigates the metal component of atmospheric particles and how it changes during physical and chemical processes at local, regional and global scales, through laboratory and field studies. In the first part of this work, the impact of local dust storms (haboobs) on ambient metal concentrations and speciation is investigated in Tempe, AZ. It was found that metal concentrations substantially increase (> 10 times) during these events before returning to pre-storm levels. In a second part of this work, the impact of fog processing on metal concentrations, solubility and speciation is examined through field observations in California’s Central Valley. The observations show that fog processing has a profound effect on local metal concentrations but the trends are not consistent between sites or even between events, indicating complex processes that need further investigation. For example, fogs have an effect on scavenging and solubility of iron in Davis, while in Fresno soluble iron content is indicative of the source of the aerosol. The last part of the thesis investigates the role of particle size on the solubilization of iron from mineral dust aerosols during global atmospheric transport through laboratory experiments. The experiments showed that mineralogy and pH have the greatest effect on iron solubility in atmospheric aerosols in general while particle size and photochemistry impact mainly the solubility of iron oxides. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2015

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