222Rn, 220Rn and their progeny concentrations in offices in Hong Kong

An active sampling system using charcoal canisters and an HPGe γ-spectrometer was employed to survey 222Rn and 220Rn concentrations in 65 offices in Hong Kong, and a traditional method was used to record simultaneously the potential α-energy concentrations (PAEC) of 222Rn and 220Rn progeny at the same sites. The mean values of gas concentration, PAEC and equilibrium factor for 222Rn were 48±32 Bq m−3, 5.2±5.1 mWL and 0.38±0.13, respectively, and the corresponding values for 220Rn were 14±7 Bq m−3, 2.7±2.1 mWL and 0.050±0.016. These values were in general higher than those in dwellings in Hong Kong, which was due to the poorer fresh air exchange in offices. Factors affecting the concentrations of 222Rn, 220Rn and their progeny were also studied. The type of air conditioners and the indoor and outdoor temperature difference show some effects on 222Rn, 220Rn and progeny concentrations, while rainfall and relative humidity affect only the progeny concentrations.