This contour map was based on annual average radon concentrations measured using alpha track detectors outdoors in Minnesota and Iowa. The spatial coverage was reasonably uniform in Iowa (111 sites). In Minnesota half of the 64 sites were located in the southwest corner of the state and the most of the rest were in the northwest.US radon concentration units are given in parentheses underneath the international units on the color scale bar. The color sacle is coordinated with the indoor radon color scale of the map just above this one. Notice that the outdoor radon in some western sections of the region (colored dark orange) is higher than it is indoors in most homes in the US (1.2 pCi/L)! Details can be found in
D. J. Steck, R. W. Field, and C. F. Lynch ; “Exposure to Atmospheric Radon”, Environmental Health Perspectives ; 107 (2),123-127; 1999
Ongoing research to try to understand why it is so high can be seen at Outdoor radon in central North America
Questions/Comments, e-mail: Dr. Steck
Last revised : 30 June, 2004
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