** Progress in Earth and Planetary Science is the official journal of the Japan Geoscience Union, published in collaboration with its 50 society members.

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    Progress in Earth and Planetary Science

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    Atmospheric and hydrospheric sciences


    Widespread distribution of radiocesium-bearing microparticles over the greater Kanto Region resulting from the Fukushima nuclear accident

    Abe Y, Onozaki S, Nakai I, Adachi K, Igarashi Y, Oura Y, Ebihara M, Miyasaka T, Nakamura H, Sueki K, Tsuruta H, Moriguchi Y

    Fukushima Daiichi Nuclear Power Plant accident, Radiocesium-bearing microparticle, Suspended particulate matter, Synchrotron radiation X-ray analysis, Trajectory analysis

    (Left) SEM images of CsMPs isolated from aerosol filter tapes collected at the greater Kanto Region on 15 March 2011. (Right) A result of forward trajectory analysis for air parcels placed above the FDNPP at 0100 JST 15 March 2011.

    The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in March 2011 emitted a considerable amount of radioactive materials. This study isolated radiocesium-bearing microparticles (CsMPs), a form of radioactive materials emitted from the FDNPP at the early stage of the accident, from aerosols collected hourly on filter tapes at seven monitoring stations at the greater Kanto Region, including the Tokyo metropolitan area, on 15 March 2011. The aerosols had a spherical shape ~ 1 μm in diameter with activity of less than 1 Bq of 137Cs per particle. Their physical and chemical characteristics, including radioactivity ratio 134Cs/137Cs as well as chemical composition and state, are essentially the same as previously reported CsMPs. This study demonstrated that air parcels containing CsMPs emitted from the FDNPP were widespread over the greater Kanto Region, more than 250 km away from the FDNPP, during the daytime of 15 March. Trajectory analysis indicated that these particles were emitted from the reactor No. 2 of FDNPP between 14 March evening and 15 March early morning. The information obtained on the widespread distribution of CsMPs can be useful for assessing the actual impacts of radioactive contamination from the FDNPP accident on the environment and human health.