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

    ** Progress in Earth and Planetary Science is partly financially supported by KAKENHI, a Grant-in-Aid from Japan Society for the Promotion of Science (Grant Number: 254001), for Publication of Scientific Research Results to enhance dissemination of information of scientific research.

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    Atmospheric and hydrospheric sciences


    The seasonal variations of atmospheric 134,137Cs activity and possible host particles for their resuspension in the contaminated areas of Tsushima and Yamakiya, Fukushima, Japan

    Takeshi Kinase et al.Kinase T, Kita K, Igarashi Y, Adachi K, Ninomiya K, Shinohara A, Okochi H, Ogata H, Ishizuka M, Toyoda S, Yamada K, Yoshida N, Zaizen Y, Mikami M, Demizu H, Onda Y

    Radiocesium, Atmospheric radioactivity, Seasonal variation, Resuspension, Fukushima, Nuclear accident, Bioaerosol, Spore, Mineral dust, Host particle

    The image of resuspension process which of the scoop for our article. The radioactive aerosols which were released from Fukushima Daiichi Nuclear Power Plant were deposited to the broad area by advection and diffusion and repeat deposition and resuspension.

    Time series of (a) radiocesium concentrations, (b) wind speeds, (c) temperatures, and (d) rain/snow precipitation. We can see two maxima in the higher concentration seasons: in May and September. The first maxima occurred with wind speed peaks, and the second maxima occurred with atmospheric temperature peaks.

    A large quantity of radionuclides was released by the Fukushima Daiichi Nuclear Power Plant accident in March 2011, and those deposited on ground and vegetation could return to the atmosphere through resuspension processes. Although the resuspension has been proposed to occur with wind blow, biomass burning, ecosystem activities, etc., the dominant process in contaminated areas of Fukushima is not fully understood. We have examined the resuspension process of radiocesium (134,137Cs) based on long-term measurements of the atmospheric concentration of radiocesium activity (the radiocesium concentration) at four sites in the contaminated areas of Fukushima as well as the aerosol characteristic observations by scanning electron microscopy (SEM) and the measurement of the biomass burning tracer, levoglucosan.

    The radiocesium concentrations at all sites showed a similar seasonal variation: low from winter to early spring and high from late spring to early autumn. In late spring, they showed positive peaks that coincided with the wind speed peaks. However, in summer and autumn, they were correlated positively with atmospheric temperature but negatively with wind speed. These results differed from previous studies based on data at urban sites. The difference of radiocesium concentrations at two sites, which are located within a 1 km range but have different degrees of surface contamination, was large from winter to late spring and small in summer and autumn, indicating that resuspension occurs locally and/or that atmospheric radiocesium was not well mixed in winter/spring, and it was opposite in summer/autumn. These results suggest that the resuspension processes and the host particles of the radiocesium resuspension changed seasonally. The SEM analyses showed that the dominant coarse particles in summer and autumn were organic ones, such as pollen, spores, and microorganisms. Biological activities in forest ecosystems can contribute considerably to the radiocesium resuspension in these seasons. During winter and spring, soil, mineral, and vegetation debris were predominant coarse particles in the atmosphere, and the radiocesium resuspension in these seasons can be attributed to the wind blow of these particles. Any proofs that biomass burning had a significant impact on atmospheric radiocesium were not found in the present study.