title: Temporal variation of post-accident atmospheric137Cs in an evacuated area of Fukushima Prefecture: Size-dependent behaviors of137Cs-bearing particles.
abstract: The concentrations of137Cs in the air, which were divided into coarse (>1.1 μm ϕ) and fine (<1.1 μm ϕ) fractions of particulate matter (PM), were measured from October 2012 to December 2014 in an area evacuated after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Total atmospheric137Cs concentrations showed a clear seasonal variation, with high concentrations during summer and autumn related to the dominant easterly wind blowing from the highly radioactivity contaminated area. This seasonal peak was dominated by137Cs in the coarse PM fraction. The137Cs specific activity (massic137Cs concentration) in the coarse PM was also found to increase significantly in summer, whereas that in the fine PM showed no variability during the year. These results show that coarse and fine137Cs-bearing PM have different origins and behaviors in the resuspension process. The seasonal variation in atmospheric137Cs concentration was well correlated with the mean137Cs surface contamination (deposition density) around the observation site weighted by the frequency of wind direction, indicating that the atmospheric137Cs concentration in the observation site was explained by the distribution of the137Cs surface contamination and the frequency of different wind directions. We introduced a resuspension factor corrected for wind direction, consisting of the ratio of the atmospheric137Cs concentration to the weighted mean137Cs surface contamination, which evaluated the intensity of resuspension better than the conventional resuspension factor. This ratio ranged from 5.7 × 10-11to 8.6 × 10-10m-1and gradually decreased during the study period.
authors.affiliation: Department of Radioecology, Institute for Environmental Sciences, 1-7 Ienomae, Obuchi, Rokkasho, Kamikita, Aomori 039-3212, Japan. Electronic address: sochiai@se.kanazawa-u.ac.jp.
authors.forename: Shinya
authors.initials: S
authors.lastname: Ochiai
authors.affiliation: Department of Radioecology, Institute for Environmental Sciences, 1-7 Ienomae, Obuchi, Rokkasho, Kamikita, Aomori 039-3212, Japan.
authors.forename: Hidenao
authors.initials: H
authors.lastname: Hasegawa
authors.affiliation: Department of Radioecology, Institute for Environmental Sciences, 1-7 Ienomae, Obuchi, Rokkasho, Kamikita, Aomori 039-3212, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Kakiuchi
authors.affiliation: Department of Radioecology, Institute for Environmental Sciences, 1-7 Ienomae, Obuchi, Rokkasho, Kamikita, Aomori 039-3212, Japan.
authors.forename: Naofumi
authors.initials: N
authors.lastname: Akata
authors.affiliation: Department of Radioecology, Institute for Environmental Sciences, 1-7 Ienomae, Obuchi, Rokkasho, Kamikita, Aomori 039-3212, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Ueda
authors.affiliation: Institute of Radiation Emergency Medicine, Hirosaki University, 66-1 Motomachi, Hirosaki City, Aomori 036-8564, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Tokonami
authors.affiliation: Department of Radioecology, Institute for Environmental Sciences, 1-7 Ienomae, Obuchi, Rokkasho, Kamikita, Aomori 039-3212, Japan.
authors.forename: Shun'ichi
authors.initials: S
authors.lastname: Hisamatsu
mesh_terms: D000396:Air Pollutants, Radioactive / Q000032:analysis*; D001272:Atmosphere / Q000737:chemistry; D002588:Cesium Radioisotopes / Q000032:analysis*; D062406:Fukushima Nuclear Accident; D010316:Particle Size; D052638:Particulate Matter / Q000032:analysis*; D011834:Radiation Monitoring
chemical_list: D000396:Air Pollutants, Radioactive; D002588:Cesium Radioisotopes; D052638:Particulate Matter
keywords: Atmospheric (137)Cs; Coarse particles; Fine particles; Fukushima Daiichi nuclear power plant accident; Resuspension