Removal of radon daughters by filtration and electric fields

The level of airborne activity of radon daughter products in indoor air may be controlled by ventilation and filtration. However ventilation with radon-free air also means introduction of colder air. Internal air filtration will not effect the radon level, but may reduce the level of the daughter activities, roughly inversely proportional to the filtration rate. The filtration may, however, also change the aerosol composition of the air, and usually increase the fraction of daughter products in the unattached state and hence increase the dose per unit of potential alpha energy concentration, delivered to the respiratory tract. Some results of the effect of filtration on the composition of radon daughters in indoor air are reported. At moderate aerosol concentrations, filtration may at a given radon level, according to some dose models, effectively decrease the dose from the daughter products, while at least one model predicts very little variation in the dose with the filtration rate. Preliminary results are also reported on measurements of the electric charge on the various daughter products, and on the possibility of lowering the daughter concentrations by exposing the air to an electric field. (author)