Ozone depletion due to dust release of iodine in the free troposphere

Low O-3 in airborne dust layers is frequently observed but poorly understood. We show that dust is a source of gas-phase iodine, indicated by aircraft observations of iodine monoxide (IO) radicals inside lofted dust layers from the Atacama and Sechura Deserts that are up to a factor of 10 enhanced over background.

Gas-phase iodine photochemistry, commensurate with observed IO, is needed to explain the low O-3 inside these dust layers (below 15 ppbv; up to 75% depleted). The added dust iodine can explain decreases in O-3 of 8% regionally and affects surface air quality. Our data suggest that iodate reduction to form volatile iodine species is a missing process in the geochemical iodine cycle and presents an unrecognized aeolian source of iodine.