On the behaviour of radon daughters in indoor air

The effect of small aerosol particles and the effect of the air cleaning devices on the behaviour of the decay products have been studied. The long term measurements in a one-family house have shown that the behaviour of the decay products is strongly dependent on both the concentration of aerosol particles (i.e. attachment rate) and the ventilation system used. By recirculating the air through a mechanical filter it was possible to reach such low particle concentrations that the deposition of the free decay products on the surfaces became important. In this case low concentrations of decay products in air were measured. When an electrostatic precipitator was used the concentration of small particles did not reach such low values as in the case of a mechanical filter. This is obviously due to the fine particle formation which is caused by corona discharge in the electrostatic precipitator. The concentration of these particles was high enough to significantly reduce the wall deposition effect. In this case the concentration of the decay products was higher than it was in the case of a conventional mechanical filter. (author)