Radon in air is ubiquitous (existing or being everywhere at the same time). Radon is found in outdoor air and in the indoor air of buildings of all kinds. EPA recommends homes be fixed if the radon level is 4 pCi/L (picocurries per liter) or more. Because there is no known safe level of exposure to radon, EPA also recommends that Americans consider fixing their home for radon levels between 2 pCi/L and 4 pCi/L.
The average indoor radon concentration for America’s homes is about 1.3 pCi/L. It is upon this national average indoor level that EPA based its estimate of 21,000 radon-related lung cancers a year. The average concentration of radon in outdoor air is .4 pCi/L or 1/10th of EPA's 4 pCi/L action level.
Read "A Citizen's Guide to Radon" at www.epa.gov/radon/citizens-guide-radon-guide-protecting-yourself-and-your-family-radon
Read about Radon Health Risks at www.epa.gov/radon/health-risk-radon
Find out how to test your home at www.epa.gov/radon/find-radon-test-kit-or-measurement-and-mitigation-professional
Find out how to fix your home by reading a "Consumer's Guide to Radon Reduction: How to Fix Your Home" at www.epa.gov/radon/consumers-guide-radon-reduction-how-fix-your-home