Preprints
https://doi.org/10.5194/acp-2021-687
https://doi.org/10.5194/acp-2021-687

  20 Sep 2021

20 Sep 2021

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

Reassessment of the radiocesium resuspension flux from contaminated ground surfaces in East Japan

Mizuo Kajino1,2,3, Akira Watanabe4,5, Masahide Ishizuka6, Kazuyuki Kita7, Yuji Zaizen1, Takeshi Kinase1,8, Rikuya Hirai9,10, Kakeru Konnai9, Akane Saya1, Kazuki Iwaoka11, Yoshitaka Shiroma12, Hidenao Hasegawa13, Naofumi Akata2, Masahiro Hosoda2, Shinji Tokonami2, and Yasuhito Igarashi7,14 Mizuo Kajino et al.
  • 1Meteorological Research Institute (MRI), Japan Meteorological Agency (JMA), Tsukuba, Ibaraki 305–0052, Japan
  • 2Institute of Radiation Emergency Medicine (IREM), Hirosaki University, Hirosaki, Aomori 036–8564, Japan
  • 3Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305–8572, Japan
  • 4Faculty of Symbiotic Systems Science, Fukushima University, Fukushima, Fukushima 960–1296, Japan
  • 5Institute for Climate Change, Fukushima, Fukushima 960–0231, Japan
  • 6Faculty of Engineering and Design, Kagawa University, Takamatsu, Kagawa 761–0396, Japan
  • 7Graduate School of Science and Engineering, Ibaraki University, Mito, Ibaraki 310–8512, Japan
  • 8Institute of Arctic Climate and Environmental Research (IACE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC) Yokohama, Kanagawa 236–0001, Japan
  • 9School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305–8572, Japan
  • 10Research Center for Advance Science and Technology (RCAST), University of Tokyo, Meguro, Tokyo 153–0041, Japan
  • 11National Institute of Radiological Sciences, National Institues for Quantum and Radiological Science and Technology, Chiba, Chiba 263–8555, Japan
  • 12Faculty of Education, University of the Ryukyus, Nishihara, Okinawa 903–0213, Japan
  • 13Institute for Environmental Sciences, Rokkasho, Aomori 039–3212, Japan
  • 14Institute for Integrated Radiation and Nuclear Science (KURNS), Kyoto University, Kumatori, Osaka 590–0494, Japan

Abstract. Resuspension of 137Cs from the contaminated ground surface to the atmosphere is essential for understanding the environmental behaviors of 137Cs and estimating external and inhalation exposure of residents. Kajino et al. (2016) assessed the 137Cs resuspension flux from bare soil and forest ecosystems in East Japan in 2013 using a numerical simulation constrained by surface air concentration measurements. However, the simulation was found to underestimate the observed deposition amounts by two orders of magnitude. The reason for this underestimation is that the simulation assumed that resuspended 137Cs is carried by submicron aerosols, which have low deposition rates. Based on the observational indications that soil dust and bioaerosols are the major carriers of resuspended 137Cs, a new simulation is performed with higher deposition rates constrained by both surface concentrations and deposition amounts. In the new estimation, the areal total annual resuspension of 137Cs in 2013 is 25.7 TBq, which is equivalent to 0.96 % of the initial deposition (2.68 PBq). Due to the rapid deposition rates, the annual redeposition amount is also large at 10.6 TBq, approximately 40 % of the resuspended 137Cs. The resuspension rate through the atmosphere (0.96 % y−1) seems slow, but it (2.6 × 10−5 d−1) may not be negligibly small compared to the actual decreasing trend of the ambient gamma dose rate obtained in Fukushima Prefecture after the radioactive decay of 137Cs plus 134Cs in 2013 is subtracted (1.0–7.9 × 10−4 d−1): Resuspension can account for 1–10 % of the decreasing rate due to decontamination and natural decay through land surface processes. The current simulation underestimated the 137Cs deposition in Fukushima city in winter by more than an order of magnitude, indicating the presence of additional resuspension sources. The site of Fukushima city is surrounded by major roads. Heavy traffic on wet and muddy roads after snow removal operations could generate superlarge (approximately 100 µm in diameter) road dust or road salt particles, which is not included in the model but might contribute to the observed 137Cs at the site.

Mizuo Kajino et al.

Status: open (until 01 Nov 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-687', Anonymous Referee #1, 29 Sep 2021 reply
  • RC2: 'Comment on acp-2021-687', Anonymous Referee #2, 19 Oct 2021 reply

Mizuo Kajino et al.

Mizuo Kajino et al.

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Short summary
Using a numerical model and observations of surface concentration and depositions, the current study provides quantitative assessments of emission, transport, and deposition of radio-Cs in East Japan in 2013, which was once deposited to the ground surface after the Fukushima nuclear accident. The areal mean resuspension rate of radio-Cs from the ground to the air is estimated as 0.96 % per year, which is equivalent to 1–10% of the decreasing rates of ambient gamma dose rate in Fukushima.
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