[M-AG34] ラジオアイソトープ移行：福島原発事故環境動態研究の新展開

[MAG34-01] Numerical and observational assessment of the impact of giant aerosol resuspension on radio-cesium deposition in winter in Fukushima

★Invited Papers

*Mizuo Kajino^1,4、Mirai Watanabe²、Naohiro Imamura³、Tomoki Kajikawa⁴、Masashi Niwano¹、Akira Watanabe^5,6 (1.Meteorological Research Institute, Japan Meteorological Agency、2.National Institute for Environmental Studies、3.Forestry an Forest Products Research Insttute、4.University of Tsukuba、5.Fukushima University、6.Institute for Climate Change)

キーワード：Resuspension, Radio-cesium, Traffic, Giant aerosols

Based on the eight-year continuous concentration and deposition measurements of radio-cesium in Fukushima city, Watanabe et al. (2022) found exceptionally high monthly cumulative deposition amounts and the monthly deposition-to-concentration ratio in the winter season, especially in January. Kajino et al. (2022) showed that a numerical simulation that considered the suppression of radio-cesium resuspension by the snow cover successfully reproduced the monthly variations of radio-cesium deposition in the restricted residential zone, Tsushima district in Namie town, while the deviations between the simulation and the observation in the residential area, Fukushima city, became larger. We therefore hypothesized that the giant aerosol resuspension (e.g., with a diameter of 100 μm or more, which can travel several hundred meters) due to snow removal work or passing vehicles or trains that carried radio-cesium deposited in the vicinity of the observation site into the deposition sampler, but not into the air sampler, since the gravitational velocity of such giant aerosols is too high to collect from the bottom of the roof of the high-volume air sampler. Route 4, Highway 4, and the railroad lines of both local and Shinkansen trains run within 1 km of the observation site, Fukushima University. To prove our hypothesis and quantify the impact of the giant aerosol resuspension, we conducted field observations and numerical simulations. We measured the radio-cesium deposition amounts at different locations in Fukushima city, at different distances from Highway 4, namely, 100 m, 300 m, and 1 km. We found that the deposition of snowmelt agents, i.e., sodium, and other trace metal compounds, increased significantly at the closer observation points (100 m and then 300m). The numerical simulation of this additional resuspension will be presented at the conference.