Role of polycyclic aromatic hydrocarbons on the photo-catalyzed solubilization of simulated soil-bound atmospheric iron

Abstract

The process of photo-oxidation of exhaust-based aromatics and the effect they have on the release of soluble iron from an otherwise insoluble soil is explored. Photo-oxidation of polycyclic aromatic hydrocarbons (PAH) has been shown to result in heavily oxidized aromatics of a wide array of molecular mass, including humic like substances (HULIS), while soluble atmospheric iron plays an essential role in carbon, sulfur, and other biogeochemical cycles, affecting the Earth's energy balance and human health. In atmospheric aerosols, anthropogenic iron emissions are observed to be much more soluble than within collected dust samples. Global production of soluble iron may be due, in part, to processing of atmospheric particulate matter by PAH emitted as anthropogenic and biomass burning products. Here, the production of soluble iron is induced by illuminating an aqueous suspension of a soil within saturated PAH bulk water matrices. Significant increases in soluble iron from soil are observed with linear PAH, including naphthalene and anthracene. Overall, results of these reactions show little correlation with resulting acidity, although acidity increases are observed in specific cases. Comparisons of PAH reactions demonstrate patterns of soluble iron production related to the formation of oxidized functional groups on the organic reagents. The data presented in this study suggest that a major pathway to the release of soluble iron is due to the formation of oxidized groups from the photo-oxidation of PAH.