Hemispheric dispersion of radioactive plume laced with fission nuclides from the Fukushima nuclear event

Abstract

Radioactivities of particulate 131 I and 137 Cs released from the Fukushima nuclear accident were monitored in a regional aerosol network including two high mountain sites (central Taiwan and Tibetan Plateau). The results were integrated with data measured elsewhere around the world, with special focus on the mid-latitudes. The hemispheric transport of the Fukushima radiation clouds (FRCs) by the westerlies took ∼18 days, displaying an exponential-like decrease eastward, with a dilution factor of at least five orders of magnitude following a full circuit around the globe. The initial two waves of FRCs may travel at different atitudes: the first one at ∼3-4 km, whereas the second one up to 5 km or more. 131 I and 137 Cs were fractionated during transport, with 137 Cs concentrated in the shallower layer, susceptible to depositional removal, while 131 I moving faster and higher. This accident may be exemplified to identify some atmospheric processes on the hemispheric scale. Copyright 2012 by the American Geophysical Union.