ABSTRACT
Iron (Fe) is the fourth most abundant element in the Earth's crust and the most abundant transition metal. Sunlight-mediated photochemical reactions of Fe(III) species in natural waters are a driving force that perturbs the chemical cycles of iron and numerous other elements away from their possible equilibrium states. In particular, the photochemical redox (photoredox) reactions of Fe(III) species are sufficiently rapid so as to affect the geochemical cycles of carbon, sulfur, phosphorus, oxygen, and, of course, iron. In order to interpret the photochemistry of Fe(III) species in natural waters, it is important to understand the likely speciation of Fe(III) in the various systems because each Fe(III) species exhibits a different intrinsic photoreactivity. The photochemical redox reactions of Fe(III) species influence chemical cycles in the atmosphere and in oceanic and surface waters. Photochemical reactions that produce oxidants are the driving force for the oxidation of Sulfur dioxide to Sulfuric acid in the troposphere.
