Radon and Thoron in the Environment - Aerosols: Measurement, Dosimetry, and Health Effects - page 542

EPA U.S. outdoor state survey
25
20
15
10
5
0
State
FIGURE 21.2 Average outdoor radon measurements made by U.S. EPA in all 50 U.S. states. (From
NAS/NRC, Health Effects of Exposure to Radon , Committee on Health Risks of Exposure to Radon, Board
on Radiation Effects Research, Commission on Life Sciences National Research Council, BEIR VI, National
Academy Press, Washington, DC, 1999a; NAS/NRC, Risk Assessment of Radon in Drinking Water , National
Research Council, National Academy Press, Washington, DC, 1999b.)
Outdoor radon measurements are not common. However, the U.S. average appears to represent
the sparse published results. A summary of published global outdoor concentrations is given in
Harley (1990). EPA has suggested target values for radon in drinking water using a multimedia
approach, which depend on the knowledge of outdoor air concentrations. Any risk from radon in
drinking water is associated with inhalation exposure from radon released during water use. The
report on the risk from radon in drinking water (NAS/NRC, 1999a,b) includes the EPA outdoor
survey. The graph of the U.S. state data is shown in Figure 21.2. The average outdoor concentration
measured in the United States is 14.8 Bq m −3 (median 14.6 Bq m −3 , maximum 35.9 Bq m −3 ).
21.6 STRATOSPHERIC CONCENTRATIONS
Radon is transported from ground release to the stratosphere by eddy turbulent diffusion and
provides information on vertical transport rates. Stratospheric air samples were collected by the
U.S. Weather Bureau (now NOAA) in 1962 to explore the possibility of using radon proiles as
an atmospheric tracer. These data were available only in an internal report until reevaluated by
Fisenne et al. (2005). In the spring of 1962, WB-57 aircraft collected tropospheric and strato-
spheric air samples by pressurizing steel gas collection spheres to a pressure of about 21 MPa at
each sampling altitude. The sampling locations were Alaska, southwest United States, and the
Panama Canal Zone at 8°, 32°, and 70° north, respectively.
Each collection sphere contained approximately 2 m 3 of air at standard temperature and pressure.
The samples were transferred through a sample train consisting of two gas washers to remove car-
bon dioxide and water vapor and then onto low background activated charcoal traps. The adsorbed
radon on the charcoal was transferred to low background (six counts per hour) 2 L ionization cham-
bers for alpha counting. The locations and trajectories of the lights were selected in order to investi-
gate the inluences of tropospheric height, the underlying land mass, and thermal gradients on radon