EVALUATION OF ROOM AIR CLEANERS FOR THE REDUCTION OF EXPOSURE AND DOSE TO INDOOR RADON PROGENY

Since the proximate source of dose to the cells of the bronchial epith elium is the deposited radon progeny, the exposure and resulting dose could be reduced if the radon decay products were effectively removed from the indoor atmosphere. Thus, room air cleaners could be effective in reducing the risks associated with indoor radon. However, because of the short half-life of Po-218, it grows back quickly and in the alt ered aerosol conditions that are produced by the presence of an air cl eaner, the exposure/dose conditions as well as the magnitude of the do se can be substantially changed. To examine the nature of the exposure of individuals in normally occupied homes and to determine the effect of various types of room air cleaners on the exposure to and dose fro m the indoor radon progeny, a series of measurements have been made us ing an automated graded screen array system. Two extended experiments were performed in homes in Amprior, Ontario, and Parishville, NY, in w hich filtration systems, a positive ion electrostatic precipitator, an d ioniser/fan systems have been tested for their ability to remove bot h airborne radioactivity and particles. In both experiments, measureme nts were made over one week periods with an air cleaner operating and the distributions of exposure are compared with measurements of the ba ckground conditions when no cleaner is functioning. The doses to both basal and secretory cells of the bronchial epithelium in the first eig ht generations of the bronchus were calculated using the model develop ed by James and their distributions are compared among the various exp osure conditions. In most cases the presence of the air cleaner reduce d the exposure to radon progeny. However, the reductions in dose, were generally substantially smaller than the reductions in exposure. In t he intercomparisons of the two filtration units and the two identical ioniser/fan systems, the units generally behaved in a similar manner. The results of this substantial set of measurements are summarised and the needs for further studies in this area described.