Uranium, Thorium and Anthropogenic Radionuclides as Atmospheric Tracers

Abstract

Anthropogenic radionuclides (137Cs, 90Sr, Pu isotopes and others) and uranium and thorium in rainwater and airborne dust are useful tracers for better understanding of atmospheric transport processes, micrometeorological processes, and natural and human induced environmental changes. Typically, analyses on spatial and temporal changes of anthropogenic radonuclides have aided to constrain the time scale of atmospheric transport of aerosols, such as stratosphere and troposphere residence times of aerosols. Although uranium and thorium in the atmosphere are used primarily as tracers of soil dust, their levels and isotope ratios have been significantly perturbed by anthropogenic sources, (e.g., fly ash and accidental releases of uranium). Therefore, uranium, thorium and their isotope ratios in airborne dust and rainwater reflect environmental changes caused by human activities and climate change. Taking into account that rates of anthropogenic radioactive fallout have recently been boosted by the resuspension of radionuclides in deposited particles, recent variations of anthropogenic radionuclides in rainwater and surface air, as well as thorium and uranium isotopes, is important tracers to study ongoing terrestrial environmental changes due to human activities.