Contribution of Asian dust to atmospheric deposition of radioactive cesium (137Cs)

Both Asian dust (kosa) transported from the East Asian continent and locally suspended dust near monitoring sites contribute to the observed atmospheric deposition of 137Cs in Japan. To estimate the relative contribution of these dust phenomena to the total 137Cs deposition, we monitored weekly deposition of mineral particles and 137Cs in spring. Deposition of 137Cs from a single Asian dust event was 62.3 mBqm−2 and accounted for 67% of the total 137Cs deposition during the entire monitoring period. Furthermore, we found high 137Cs specific activity in the Asian dust deposition sample. Although local dust events contributed to 137Cs deposition, their contribution was considerably smaller than that of Asian dust. We conclude that the primary source of atmospheric 137Cs in Japan is dust transported from the East Asian continent.