Deposition of 137CS in Rokkasho, Japan and its relation to Asian dust

Biweekly atmospheric depositions of Cs-137 were measured in Rokkasho, Aomori, Japan from March 2000 to March 2006 to study recent Cs-137 deposition. Although the deposition level was generally lower than the detectable limit, deposition samples collected in spring occasionally had measurable levels of Cs-137. The annual Cs-137 deposition from 2001 to 2005 was 0.04-0.69Bqm(-2) with a mean value of 0.27 Bq m(-2). Depositions of insoluble Al, Fe and Ti were strongly correlated with the Cs-137 deposition, suggesting that suspension of soil particles was the main source of the recent Cs-137 deposition. Asian dust events were coincident with some of the significant Cs-137 depositions in spring. It was found that the ratios of Cs-137/Al and Fe/Al could be used as indices for discriminating Asian dust from suspension of the local surface soil. Backward trajectory analysis suggested southern Mongolian and northeastern China regions as sources of the significant Cs-137 depositions. (c) 2007 Elsevier Ltd. All rights reserved.