title: Depositional fluxes and residence time of atmospheric radioiodine (131I) from the Fukushima accident.
abstract: Activities of radioiodine ((131)I) along with (210)Pb and (210)Po in time series precipitation samples were measured to determine the depositional fluxes of (131)I in the Southern United States and its removal rate and residence time in the atmosphere during the Fukushima nuclear accident. Radioiodine released from the Fukushima accident reached the Southern United States within 11 days, giving rise to a concurrent (131)I peak and anomalous (210)Po/(210)Pb ratios in the precipitation samples. The cumulative (131)I depositional flux was 4.6 ± 0.2 Bq m(-2) during the maximum fallout. The removal rate of (131)I out of the atmosphere, derived from a definite (131)I integral model, ranged from 0.03 to 0.14 d(-1) with an average of 0.08 ± 0.02 d(-1), which corresponds to a residence time of (131)I in the atmosphere of 12 ± 3 days, consistent with the resident timescale constrained by the (210)Po/(210)Pb disequilibrium technique. These results support our hypothesis that radioiodine was removed from the atmosphere by precipitation within two weeks. It seemed that regions reachable by (131)I transport within two weeks from Fukushima Japan would receive much more fallout, whereas places outside that distance would be relatively less polluted with radionuclides.
authors.affiliation: Department of Marine Science, University of Southern Mississippi, 1020 Balch Blvd., Stennis Space Center, MS 39529, USA.
authors.forename: Weifeng
authors.initials: W
authors.lastname: Yang
authors.forename: Laodong
authors.initials: L
authors.lastname: Guo
mesh_terms: D000396:Air Pollutants, Radioactive / Q000032:analysis*; D062406:Fukushima Nuclear Accident; D007457:Iodine Radioisotopes / Q000032:analysis*; D007564:Japan
chemical_list: D000396:Air Pollutants, Radioactive; D007457:Iodine Radioisotopes