Evaluation of the Effectiveness of Several Air Cleaners for Reducing the Hazard from Indoor Radon Progeny

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Abstract
In studies conducted in the early 1980s, it was suggested that the use of room-type air cleaners were relatively ineffective in reducing the hazards associated with the presence of radon decay products in indoor air. Some studies suggested that air cleaning could actually increase the dose delivered by the decay products by shifting the activity-weighted particle size distribution to smaller sizes to the point where dose increase even though exposure decreased. A recently developed automated, semicontinuous instrument now permits the direct measurement of activity-weighted size distributions in occupied homes so that the exposure to those occupants can be directly determined and the effect of the air cleaners on dose be estimated. Three different types of air cleaners were tested in this study; an electrostatic air cleaner (EAC), an ion generator / fan system (IG / F), and a filtration unit that was operated at two different fan speeds (LO-FIL and HI-FIL). The three units reduced the median exposure to radon progeny by 63% for the EAC, 34% for the IG / F unit, 66% for the filtration system at both low and high flow rates. Based on a model for lung dosimetry, the median reductions is estimated dose to the secretory cells of the bronchial epithelium are 50% for the EAC, 28% for the IG / F unit, and 68% for the filtration system at both fan speeds. In these studies, the performance of the EAC and filtration systems produce rather similar activity weighted size distributions while the lower dose reduction for the IG / F system is due to a small peak in activity in the size range of 1.5–5 nm. The source of this peak is not known, and requires further study to determine if the system is generating particles in this size range