Deposition and Dispersion of Radio‐Cesium Released due to the Fukushima Nuclear Accident: 2. Sensitivity to Aerosol Microphysical Properties of Cs‐Bearing Microparticles (CsMPs)

The dispersion and deposition of radio‐cesium (137Cs) carried by two types (type A and type B) of water‐insoluble Cs‐bearing solid microparticles (CsMPs) released due to the Fukushima nuclear accident were simulated for the first time. The presence of type B CsMPs (70–400 μm found in soil and 1–5 μm...

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Bibliographic Details
Published in:Journal of geophysical research. Atmospheres 2021-01, Vol.126 (1), p.n/a
Main Authors: Kajino, Mizuo, Adachi, Kouji, Igarashi, Yasuhito, Satou, Yukihiko, Sawada, Morihiro, Thomas Sekiyama, Tsuyoshi, Zaizen, Yuji, Saya, Akane, Tsuruta, Haruo, Moriguchi, Yuichi
Format: Article
Language:English
Subjects:
Aerosol properties
Chemical transport model
CsMPs
Deposition processes
Fukushima nuclear accident
Radiocesium
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Summary:The dispersion and deposition of radio‐cesium (137Cs) carried by two types (type A and type B) of water‐insoluble Cs‐bearing solid microparticles (CsMPs) released due to the Fukushima nuclear accident were simulated for the first time. The presence of type B CsMPs (70–400 μm found in soil and 1–5 μm found in air), associated with the hydrogen explosion of Unit 1 in the afternoon of March 12, could partly explain the simulated underestimation of total deposition over land by assuming that 100% of the Cs carriers were water‐soluble submicron particles (WSPs). Type A CsMPs (0.1–10 μm), released from Units 2 or 3 in the midnight between March 14 and 15, traveled over the Kanto Plain, the most populated plain in Japan. Differences in the size distribution of type A CsMPs altered the surface air concentration over Kanto substantially, by up to more than one order of magnitude. The major deposition mechanisms varied among dry, wet, and fog (and/or cloud) depositions depending on the size distribution and locations. The simulated activity fractions due to the CsMPs in the total deposition were compared to those observed in surface soil for the first time. The observations could be explained by the simulations for the locations under the influence of type B CsMPs. However, the simulations were substantially underestimated for the locations influenced by type A CsMPs. There could be more fractions of type A CsMPs emission in the source term and/or the simulated deposition rates of type A CsMPs were underestimated. Key Points The regional impacts of two types (A and B) of Cs‐bearing solid microparticles (CsMPs) were numerically examined for the first time Type B CsMPs could partly explain the underestimation of simulated total deposition over land The environmental behaviors of type A CsMPs could vary substantially depending on size
ISSN:2169-897X
2169-8996
DOI:10.1029/2020JD033460