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Frequency distribution of average seasonal ambient radon for the United States.
15 Bq m-3 for the United States and that it lies within a confidence interval of 14–16 Bq m-3.
It is evident that radon concentrations in air, in water, and indoors vary systematically across the United States and that this variation should be part of any regional consideration of multimedia assessment and mitigation. A comprehensive, geographically based ambient-radon study that incorporates the major population areas of the United States and their geologic variability would provide the basis for a valid population-weighted ambient radon concentration. Focused regional studies of ambient radon in high-radon areas such as the glaciated northern tier of states and states of the Appalachian Mountains, Rocky Mountains, and Basin and Range would yield better information on overall exposure and more-realistic baseline information for evaluating the contribution of the ambient concentration to what is observed in indoor air.