Indoor dose conversion coefficients for radon progeny for different ambient environments

Inhaled progeny of 222Rn (radon progeny) are the most important source of irradiation of the human respiratory tract. Their attachment to atmospheric aerosols follows a well-established relationship between the activity size distribution (ASD) and the number size distribution. Recent studies have shown that indoor aerosols are derived primarily from outdoor sources, so it is pertinent to study the effects of different ambient environments on the indoor radon dose (in terms of the dose conversion coefficient or DCC, in units of mSv WLM-1). Commonly encountered ambient aerosols were studied here, which included the traffic-, urban-, and marine-influenced aerosols. The ASDs of attached radon progeny for all three studied ambient environments were well-represented by normal distributions. From these ASDs, the DCCs were calculated using the ICRP66 model and the scaled Yeh-Schum model. All other employed parameters were adopted from original references or authoritative reports. The DCCs for a nominal home calculated using the James model and the Yeh-Schum model were 12 and 8 mSv WLM-1, respectively. The DCCs were largest for urban-influenced ambient environments and smallest for marine-influenced ambient environments, and those for traffic-influenced ambient environments were close to that for a nominal home. If we adopt the stochastic model, the probability of contracting radon-induced lung cancer by a person living with a marine-influenced ambient environment will be half that of a person living with an urban-influenced ambient environment.