Chapter 8 - Iodine in the Air: Origin, Transformation, and Exchange to Mammals

Abstract

This chapter focuses on different processes and the variety of gas- and aerosol-phase species that constitute the terrestrial iodine cycle. It includes discussion of the origin and measurement of atmospheric iodine in its various forms, the principal photochemical pathways in the gas phase, and the role of aerosol uptake and chemistry and new particle production. As part of the biogeochemical cycle, the injection of iodine-containing gases into the atmosphere, and their subsequent chemical transformation therein, play a crucial role in environmental and health aspects associated with iodine—most importantly, in determining the quantity of the element available to the mammalian diet. The main sources of atmospheric iodine are biogenic, i.e., phytoplankton in the open ocean and certain seaweed species at coastal sites, with some likely contribution from chemical transformation of I2 in seawater. Oxidation of I atoms with ozone (O3) in the lower atmosphere produces the IO molecule, which is subject to a number of subsequent reaction channels. The major impact of atmospheric iodine chemistry is the resultant depletion of O3, while other consequences, such as enhanced cloud formation, remain to be established. The chemical transformation of iodine overlaps with the chemistry of other halogen species, chlorine and bromine.