Long-term assessment of airborne radiocesium after the Fukushima nuclear accident: re-suspension from bare soil and forest ecosystems
Long-term assessment of airborne radiocesium after the Fukushima nuclear accident: re-suspension from bare soil and forest ecosystems
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DOI：
10.5194/acp-16-13149-2016
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发表时间：
2016-10-27
影响因子：
6.3
通讯作者：
Inatsu, Masaru
中科院分区：
文献类型：
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作者：
Kajino, Mizuo;Ishizuka, Masahide;Inatsu, Masaru
通过数值模拟、污染地区(福岛县浪江镇)粉尘排放通量的现场实验以及污染地区内外(茨城县筑波市)空气浓度的测量，对福岛核事故造成的土壤和森林中Cs-137再悬浮的长期影响进行了定量评估。为了评估长期效果，在实地试验开始后，选择了2013年的全年进行研究。浪江县和筑波的Cs-137浓度分别约为10(-1)-1和10(-2)-10(-1)mBqm(-3)。浪江县的月浓度中位数比筑波的高1至2个数量级。这两个测点之间的观测差异与模拟差异是一致的，表明Cs-137再悬浮和大气传输的模拟是成功的。估计的再悬浮率约为10(-6)天(-1)，显著低于福岛县环境伽马剂量率的下降率(10(-4)-10(-3)天(-1))，这是放射性衰变、土壤和生物群迁移以及去污的结果。因此，重新悬浮对减少地面放射性的贡献微乎其微。扬尘模型能较好地再现冬季的Cs-137浓度，而夏季的浓度被低估了1~2个数量级。以10(-7)h(-1)的固定速率从森林中悬浮下来，再乘以绿地面积分数，可以解释浪江县空气中Cs-137的浓度及其季节变化。模拟两地沙尘再悬浮对空气浓度的贡献，冷季为0.7-0.9，暖季为0.2-0.4，其余为森林再悬浮。重新悬浮的机制，特别是通过森林生态系统的重新悬浮机制仍不清楚。这是第一项对放射性铯再悬浮的长期评估提供粗略估计的研究。更多的研究活动应调查长期管理重新暂停的进程/机制。这可以通过进行更多的现场实验和数值模拟来实现。
The long-term effect of Cs-137 re-suspension from contaminated soil and forests due to the Fukushima nuclear accident has been quantitatively assessed by numerical simulation, a field experiment on dust emission flux in a contaminated area (town of Namie, Fukushima prefecture), and air concentration measurements inside (Namie) and outside (city of Tsukuba, Ibaraki prefecture) the contaminated area. In order to assess the long-term effect, the full year of 2013 was selected to study just after the start of the field experiments. The Cs-137 concentrations at Namie and Tsukuba were approximately 10(-1)-1 and 10(-2)-10(-1) mBqm(-3), respectively. The observed monthly median concentration at Namie was 1 to 2 orders of magnitude larger than that at Tsukuba. This observed difference between the two sites was consistent with the simulated difference, indicating successful modeling of Cs-137 re-suspension and atmospheric transport. The estimated re-suspension rate was approximately 10(-6) day(-1), which was significantly lower than the decreasing rate of the ambient gamma dose rate in Fukushima prefecture (10(-4)-10(-3) day(-1)) as a result of radioactive decay, migration in the soil and biota, and decontamination. Consequently, re-suspension contributed negligibly in reducing ground radioactivity. The dust emission model could reproduce the air concentration of Cs-137 in winter, whereas the summer air concentration was underestimated by 1 to 2 orders of magnitude. Re-suspension from forests at a constant rate of 10(-7) h(-1), multiplied by the green area fraction, could explain the air concentration of Cs-137 at Namie and its seasonal variation. The simulated contribution of dust resuspension to the air concentration was 0.7-0.9 in the cold season and 0.2-0.4 in the warm season at both sites; the remainder of the contribution was re-suspension from forest. The re-suspension mechanisms, especially through the forest ecosystems, remain unknown. This is the first study that provides a crude estimation of the long-term assessment of radiocesium re-suspension. Additional research activities should investigate the processes/mechanisms governing the re-suspension over the long term. This could be achieved through conducting additional field experiments and numerical simulations.