Estimation of the Global 222Rn Flux Density from the Earth's Surface

DOI DOI Web Site 被引用文献4件 参考文献43件
  • HIRAO Shigekazu
    Department of Energy Engineering and Science, Graduate School of Engineering, Nagoya University
  • YAMAZAWA Hiromi
    Department of Energy Engineering and Science, Graduate School of Engineering, Nagoya University
  • MORIIZUMI Jun
    Department of Energy Engineering and Science, Graduate School of Engineering, Nagoya University

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Global 222Rn flux density distributions with a spatial resolution of 1° in latitude and longitude were estimated for each month in the period of 1979-2007 using an 222Rn exhalation model based on a porous media diffusion theory. This exhalation model calculated the 222Rn flux density as a function of the 226Ra content, soil water saturation, and soil temperature. The influence of the topographical ruggedness of the ground surface on the flux density was also considered in the model. The global average of the flux density during the 29-year period was estimated to be 21.3 mBq m-2 s-1. The annual variation in the globally averaged flux density showed a slight but steady increase since 1999. The seasonal variation in the globally averaged flux density was estimated to range from a minimum of 18.8 mBq m-2 s-1 in March to a maximum of 23.6 mBq m-2 s-1 in September. The regional averages for the annual flux density varied from 8.3 mBq m-2 s-1 for the northern part of North America to 33.5 mBq m-2 s-1 for Australia. The latitudinal distribution of zonally averaged flux density was found to be in good agreement with the latitudinal decline at high latitudes in the Northern Hemisphere. The spatial and temporal variations were caused mainly by variations in the soil water content and soil 226Ra content, but to a lesser extent by the soil temperature. The topographical ruggedness was found to increase the flux density by only 2% globally but by more than 10% in mountainous regions. Atmospheric transport simulations using the estimated flux density as input data showed that the simulated atmospheric 222Rn concentration was substantially lower than that measured at Hachijo Island, implying that the flux density of the present study with topographical ruggedness is still underestimated in the East Asian region.

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  • 保健物理

    保健物理 45 (2), 161-171, 2010

    日本保健物理学会

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