A Review of Indoor and Outdoor Radon Equilibrium Factors-part I: 222Rn.

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 Rn 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.