Dose Reduction Effects of Face Masks against Radon Progeny Inhalation (2): Changes in Aerosol-attached Radon Progeny Concentrations before and after Passing through Face Masks and Resulting Dose Reduction Effects

In a previous report of the authors, changes in aerosol number concentrations before and after passing through four types of masks (non-woven masks, N-95 masks, urethane masks, and gauze masks) were investigated. In the present study, reduction rates of aerosol-attached radon progeny concentrations were calculated from the changes in aerosol number concentrations and attachment coefficients for four particle size ranges, based on a theory of attachment of radon progeny to aerosol particles. Additionally for comparison, reduction rates of radon progeny concentrations before and after passing through the masks were measured by an alpha-counting method. The calculated and measured reduction rates were in good agreement. Reduction rates of inhalation dose due to radon progeny were estimated for the four types of masks at the same two experimental conditions as in the previous study. The reduction rates for the four types of masks were 23 to 99.5% for experiments without simulation of a person wearing a mask. Those for the same masks were 31% to 75% for experiments with simulation of a person wearing a mask. The results for experiment at the two different conditions indicated that the reduction rates depended on the adhesiveness of the mask to the face as well as the mask types.