Long-range transport of continental radon in subantarctic and antarctic areas

Gaseous Rn-222, a daughter product of U-238, is injected into the atmosphere from the surface of continents. Its atmospheric cycle is particularly simple since it disappears only by radioactive decay (half-life 3.8 days). Radon measurements obtained over more than 15 years in remote stations in Antarctic and Subantarctic areas generally give concentrations as low as 0.1 to 2 pCi·m^-3. However, we have shown the existence of sharp increases of concentrations reaching 3 to 30 pCi·m^-3 called “radonic storms”. Owing to the negligible degassing of radon from the sea surface, such peaks are accounted for by long-range transport from remote continents (mainly South Africa) over Southern Indian and Antarctic oceans, with transit times ranging from 1.5 to 7 days and very low dilution factors of the order of 3 to 7. This airmass transport is related to warm sectors of cyclonic systems passing over South Africa and around the Antarctic continent.