Using a homemade code named DIRAP2 for calculating effective doses from radon (²²²Rn) progeny, the authors investigated dependence of the effective dose per exposure on aerosol parameter values in workplaces and residences. The dependence of the effective dose per exposure on the unattached fraction, f_p, and the fraction of potential alpha energy concentration in the nucleation mode, f_pn, was approximated as a function of f_p and f_pn. By substituting site-specific values of f_p and f_pn into these approximation formulae, the effective dose per exposure at any given location can be easily estimated. Regarding particle size dependence, relative values of the effective dose per exposure for various particle diameters with reference to that at the reference particle diameter were calculated and tabulated. The above-mentioned approximation formulae and the relative values were determined for Reference Individuals of various ages and physical activity levels. This enables calculation of the effective dose for arbitrary time-activity patterns, which may differ from those assumed in the reference ICRP time allocation.