THE DEPOSITION OF UNATTACHED RADON PROGENY IN A TRACHEOBRONCHIAL CASTAS MEASURED WITH IODINE VAPOR

The deposition of the unattached radon progeny in hollow cast models o f the human tracheobronchial region was studied using iodine vapor. Th e experiments were conducted in a replicate cast whose inner surface w as coated with NaOH impregnated charcoal powder. This coating can trap iodine molecules by converting iodine into iodide and iodate, so that the iodine gas molecules behave like particles and stick to the surfa ce upon contact. The iodine vapor is selected as a surrogate of radon progeny because the effective diffusion coefficient of iodine vapor, 0 .08 cm(2) s(-1), is close to the diffusivities of unattached radon pro geny (0.03-0.07 cm(2) s(-1)). Deposition experiments have been conduct ed under constant and cyclic inspiratory Bow between 5 and 30 LPM. It was found that the deposition of iodine vapor under constant flow can be described by diffusion in laminar flow. The cyclic inspiratory flow pattern does not significantly change the total deposition in the tra cheobronchial cast. This observation, combined with the enhanced parti cle deposition due to charge (Cohen ct al., 1996) suggest that particl e charge plays an important role in the deposition of submicron partic les in human airways. (C) 1998 American Association for Aerosol Resear ch.