The dispersion and deposition of radio‐cesium (¹³⁷Cs) carried by two types (type A and type B) of water‐insoluble Cs‐bearing solid microparticles (CsMPs) released due to the Fukushima nuclear accident were simulated for the first time. The presence of type B CsMPs (70–400 μm found in soil and 1–5 μm found in air), associated with the hydrogen explosion of Unit 1 in the afternoon of March 12, could partly explain the simulated underestimation of total deposition over land by assuming that 100% of the Cs carriers were water‐soluble submicron particles (WSPs). Type A CsMPs (0.1–10 μm), released from Units 2 or 3 in the midnight between March 14 and 15, traveled over the Kanto Plain, the most populated plain in Japan. Differences in the size distribution of type A CsMPs altered the surface air concentration over Kanto substantially, by up to more than one order of magnitude. The major deposition mechanisms varied among dry, wet, and fog (and/or cloud) depositions depending on the size distribution and locations. The simulated activity fractions due to the CsMPs in the total deposition were compared to those observed in surface soil for the first time. The observations could be explained by the simulations for the locations under the influence of type B CsMPs. However, the simulations were substantially underestimated for the locations influenced by type A CsMPs. There could be more fractions of type A CsMPs emission in the source term and/or the simulated deposition rates of type A CsMPs were underestimated.

中文翻译：

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由于福岛核事故而释放的放射性铯的沉积和扩散：2.对含Cs微粒（CsMPs）的气溶胶微物理性质的敏感性

铯的扩散和沉积（¹³⁷首次模拟了由于福岛核事故而释放出的两种类型（A型和B型）水不溶性Cs固体微粒（CsMPs）携带的Cs。B型CsMP的存在（在土壤中发现70-400μm，在空气中发现1-5μm），与3月12日下午1号机组的氢爆炸有关，可能部分解释了模拟低估了陆地上的总沉积量假设100％的Cs载体是水溶性亚微米颗粒（WSP）。3月14日至15日午夜从第2或第3单元释放的A型CsMP（0.1-10μm）在日本人口最多的关东平原上空行驶。A型CsMPs大小分布的差异大大改变了关东地区的地表空气浓度，最多可超过一个数量级。主要的沉积机理在干，湿和雾（和/或云）沉积之间有所不同，具体取决于尺寸分布和位置。将总沉积物中CsMPs引起的模拟活性分数与首次在表层土壤中观察到的那些进行了比较。可以通过模拟在B型CsMPs影响下的位置来解释这些观察结果。但是，对于A型CsMP所影响的位置，该模拟被大大低估了。在源项中可能会有更多的A型CsMPs排放分数和/或低估了A型CsMPs的模拟沉积速率。将总沉积物中CsMPs引起的模拟活性分数与首次在表层土壤中观察到的那些进行了比较。可以通过模拟在B型CsMPs影响下的位置来解释这些观察结果。但是，对于A型CsMP所影响的位置，该模拟被大大低估了。在源项中可能会有更多的A型CsMPs排放分数和/或低估了A型CsMPs的模拟沉积速率。将总沉积物中CsMPs引起的模拟活性分数与首次在表层土壤中观察到的那些进行了比较。可以通过模拟在B型CsMPs影响下的位置来解释这些观察结果。但是，对于A型CsMP所影响的位置，该模拟被大大低估了。在源项中可能会有更多的A型CsMPs排放分数和/或低估了A型CsMPs的模拟沉积速率。