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A Review of Indoor and Outdoor Radon Equilibrium Factors—part I


Chen, Jing1; Harley, Naomi H.2

doi: 10.1097/HP.0000000000000909

Radon exposure limits are given in terms of radon gas concentration in the air. However, in the calculation of radon dose to the lung, the radon equilibrium equivalent concentration is used. The measured equilibrium factor times the measured radon gas concentration estimates the equilibrium equivalent concentration. Therefore, the equilibrium factor is an important factor in radon dose calculations. A review of published measurements of equilibrium factors shows a range of values reported in studies from more than 20 countries, measured in indoor residential, indoor public, and outdoor environments. Values for 222Rn are reported and discussed here, with special attention paid to results from India and China, where measured equilibrium factors are reported for hundreds and thousands of households, respectively. The wide range of equilibrium factors suggests that location-specific values are more appropriate than a worldwide average value in the calculation of lung bronchial dose.

1Radiation Protection Bureau, Health Canada, 775 Brookfield Road, Ottawa K1A 1C1, Canada;

2New York University School of Medicine, 1 Marine View Plaza, Hoboken, NJ.

The authors declare no conflicts of interest.

For correspondence contact: Jing Chen, Radiation Protection Bureau, Health Canada, 775 Brookfield Road, Ottawa K1A 1C1, Canada, or email at

(Manuscript accepted 23 April 2018)

© 2018 by the Health Physics Society