Preprints
https://doi.org/10.5194/acp-2021-591
https://doi.org/10.5194/acp-2021-591

  30 Jul 2021

30 Jul 2021

Review status: this preprint is currently under review for the journal ACP.

Eight-year variations in atmospheric radiocesium in Fukushima City

Akira Watanabe1,2, Mizuo Kajino3,4,5, Kazuhiko Ninomiya6,7, Yoshitaka Nagahashi1, and Atsushi Shinohara6 Akira Watanabe et al.
  • 1Faculty of Symbiotic Systems Science, Fukushima University, Fukushima, Fukushima 960-1296, Japan
  • 2Institute for Climate Change, Fukushima, Fukushima 960-0231, Japan
  • 3Meteorological Research Institute (MRI), Japan Meteorological Agency (JMA), Tsukuba, Ibaraki 305-0052, Japan
  • 4Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan
  • 5Institute of Radiation Emergency Medicine (IREM), Hirosaki, Aomori 036-8564, Japan
  • 6Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
  • 7Intitute for Radiation Sciences, Osaka University, Toyonaka, Osaka 560-0043, Japan

Abstract. After the Fukushima nuclear accident, atmospheric 134Cs and 137Cs measurements were taken in Fukushima city for eight years, from March 2011 to March 2019. The surface air concentrations and deposition of radio-Cs were high in winter and low in summer; these trends are the opposite of those observed in a contaminated forest area. The half-lives of 137Cs in the concentrations and deposition before 2015 (275 d and 1.11 y) were significantly shorter than those after 2015 (756 d and 4.69 y). The dissolved fractions of precipitation were larger than the particulate fractions before 2015, but the particulate fractions were larger after 2016. The half-lives of 137Cs in the concentrations and deposition were shorter before 2015, probably because the dissolved radio-Cs was discharged from the local terrestrial ecosystems more rapidly than the particulate radio-Cs. X-ray fluorescence analysis suggested that biotite may have played a key role in the environmental behavior of particulate forms of radio-Cs after 2014. However, the causal relationship between the seasonal variations in particle size distributions and the possible sources of particles is not yet fully understood. The current study also proposes a method of evaluating the consistency of a numerical model for radio-Cs resuspension and suggests that improvements to the model are necessary.

Akira Watanabe et al.

Status: open (until 13 Oct 2021)

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Akira Watanabe et al.

Akira Watanabe et al.

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Short summary
This study summarizes continuous measurements of surface concentrations and deposition of radiocesium in Fukushima city over eight years after the Fukushima nuclear accident. The concentration in the city was high in winter and low in summer, opposite from the forest area. The decreasing trends were much faster in the earlier stage, probably because dissolved cesium discharged faster from local environment. Biotite might play a key role on circulation of particulate cesium in Fukushima city.
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