SIZE-SPECIFIC INDOOR AEROSOL DEPOSITION MEASUREMENTS AND DERIVED I O CONCENTRATIONS RATIOS/

The process of aerosol deposition on indoor surfaces has implications for human exposure to particulate contaminants of both indoor and outd oor origin. In the radiological context, current accident models assum e a uniform Dose Reduction Factor (DRF) of 0.5 for indoor residence du ring the outdoor passage of a radioactive aerosol cloud. To examine th e general validity of this figure, indoor aerosol deposition have been determined in four houses. Monodisperse aerosol particles, with mass median aerodynamic diameters (MMAD) in the range 0.5-5.5 mu m, were la belled with neutron-activatable tracers and dispersed in unfurnished a nd furnished rooms; the decay rate of the particles was then inferred from analysis of sequential air samples. Allowing for the differences in furnishing and level of occupancy between the tests, consistent aer osol deposition velocities were determined and, for furnished rooms, t he following empirical expression, relating the particles' MMAD (d(p), in mu m) to the indoor deposition velocity (upsilon(d), in 10(-4) m s (-1)) was derived: upsilon(d) = 0.48 + 0.60 d(p) (r = 0.93). Using thi s formula, particle size-specific DRFs were determined and found to be in good agreement with previous measurements of I/O ratios for fine a nd coarse particles. It was concluded that, for realistic dose estimat es, a radioisotope-specific factor may be merited. (C) 1997 Elsevier S cience Ltd.