Eight-year variations in atmospheric radiocesium in Fukushima City

Watanabe, Akira; Kajino, Mizuo; Ninomiya, Kazuhiko; Nagahashi, Yoshitaka; Shinohara, Atsushi

doi:10.5194/acp-2021-591

Cited by 1 publication

(11 citation statements)

References 22 publications

(55 reference statements)

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“…The numerical simulations conducted by K16 were consistent with the findings described above: the surface concentrations in the mountainous forest area are low in winter and high in summer, the contributions of mineral dust are high in winter, and those of bioaerosols are high in summer. However, Watanabe et al (2021) found that the simulations of K16 underestimated the observed deposition amounts by approximately two orders of magnitude. The major reason for this large discrepancy in deposition is the incorrect assumption of the physical properties of resuspended 137 Cs by K16.…”

Section: Introductionmentioning

confidence: 91%

“…1). The concentration and deposition measurements are conducted at Fukushima University (140.45°E, 37.68°N) (Watanabe et al, 2021). Fukushima University is located on a small hill at the southern edge of the Fukushima Basin and is surrounded by major roads.…”

Section: Observation Datamentioning

confidence: 99%

“…Decontamination was conducted in 2013 in Fukushima city, and almost 90% of decontamination was completed for agricultural fields and public facilities by March 2014 (Watanabe et al, 2021). The achievement ratios of decontamination for other land use types are 50%, 9%, and 5% for residential areas, roads, and forests (only living areas; the removal of shrub and litter layers within 20 meters from the forest edges), respectively (Watanabe et al, 2021). The sampling intervals of the concentration and deposition measurements at this site are 3 days and 1 month, respectively.…”

Section: Observation Datamentioning

confidence: 99%

“…K16 had two major drawbacks: (1) K16 constrained the deposition parameters (i.e., E c and v d ) by using the primary 137 Cs emission and initial 137 Cs deposition amounts measured in March 2011, and (2) K16 did not compare their simulation results against the deposition amounts. Recently, Watanabe et al (2021) evaluated the performance of the K16 model using concentrations and deposition amounts measured at Fukushima sites and found that the seasonal variations in simulated concentrations were opposite to those observed and that the simulated deposition amounts were underestimated by one to two orders of magnitude. The reason for this underestimation of the deposition amounts is obvious; the typical deposition rates of major carrier aerosols (submicron aerosols) are much smaller than the resuspension rates (supermicron aerosols).…”

Section: Constraint Of Modeled Deposition Parametersmentioning

confidence: 99%

“…On the other hand, Adachi et al (2013) isolated hydrophobic supermicron Cs-bearing particles (referred to as Cs-bearing microparticles; CsMPs) from aerosol filters collected in March 2011; the atmospheric behaviors of these CsMPs could be quite different from those of hydrophilic submicron particles. Detailed analyses of CsMPs are helpful for understanding emission events and mechanisms (Igarashi et al, 2019a;Kajino et al, 2021) and deposition processes (Dépée et al, 2019). Vertical measurements obtained on mountains (Hososhima and Kaneyasu, 2014;Sanada et al, 2018) have revealed the importance of cloud deposition over mountainous forests in East Japan.…”

Section: Introductionmentioning

confidence: 99%

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

Kajino

Watanabe

Ishizuka

et al. 2021

Preprint

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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.

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Section: Introductionmentioning

confidence: 91%

Section: Observation Datamentioning

confidence: 99%