Background atmospheric 222Rn concentrations outdoors and indoors: a review.

The sources of outdoor and indoor atmospheric radon are examined. The variation of outdoor atmospheric radon with time of day, time of year, altitude and geographic location is quantitatively assessed. Average values of outdoor atmospheric radon concentrations are examined and it is estimated that the mean value for normal areas of the contiguous United States lies in the range of 100-400 pCi/m3 and is probably about 250 pCi/m3. Values for Alaska and Hawaii are an order of magnitude lower. Indoor atmospheric radon concentrations are found to vary with time of day, geographic location and story above ground.