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The factors affecting indoor radon properties in Hong Kong have been studied, including the radon concentration, the total potential alpha energy concentration of radon progeny, the equilibrium factor, and the fraction of unattached radon progeny. These factors fall into three categories, namely, (1) the building characteristics, including cooling method, age of the buildings, wall coverings and floor coverings; (2) the location of sites, including nearby environments, geological materials of the area, and the elevation of the sites; and (3) the meteorological parameters, including rainfall, relative humidity, pressure, temperature, and wind speeds. For category (1), only the ventilation is found to affect the indoor radon properties. For category (2), only the nearby environments have effects. For category (3), the rainfall and temperature are found to have significant effects.

The potential alpha energy concentrations of radon and thoron progeny have been surveyed for dwellings in Hong Kong and the mean values are obtained as 3.58 and 2.29 mWL, respectively. The relative importance of the value for thoron is unexpectedly high, which is attributed to the high 232Th content of the building materials used in Hong Kong. It has also been found that the potential alpha energy concentration values for radon progeny changed dramatically with the season due to the different aerosol contents in the air in different seasons. The factors affecting the potential alpha energy concentration values have also been studied. These factors fall into three categories, namely (1) the building characteristics including age of the buildings, wall coverings and floor coverings; (2) the location of sites including nearby environments and the elevation of the sites; and (3) the meteorological parameters including wind speed, atmospheric pressure, air temperature and relative humidity. For categories (1) and (2), all factors seem to affect the potential alpha energy concentration values, although the effects may be different for radon and thoron progeny, which may be due to the very much different half lives of radon and thoron gas and to the different behavior of radon and thoron progeny in the attachment to aerosols. For category (3), only wind speed has been found to have effects.