Indoor radon distribution of subway stations in a Korean major city

The overall survey on indoor radon concentration was conducted at all subway stations in a major city, Daejeon in the central part of Korea. It was quarterly performed from September 2007 to August 2008. The annual arithmetic mean of indoor radon concentration of all the stations was 34.1 ± 14.7 Bq m−3, and the range of values was from 9.4 to 98.2 Bq m−3. The radon concentrations in groundwater (average 31.0 ± 0.8 Bq m−3) were not significantly high in most stations, but the concentration (177.9 ± 2.3 Bq L−1) of one station was over the level of 148 Bq L−1 in drinking water proposed by U.S. EPA. Based on indoor survey results, the approximate average of the annual effective dose by radon inhalation to the employees and passengers were 0.24 mSv y−1, and 0.02 mSv y−1, respectively. Although the effective dose based on the UNSCEAR report was potentially estimated, for more accurate assessment, the additional survey on the influence by indoor radon will be necessary.