Indoor Concentration Simulation of Radon Isotopes and Their Decay Products

The indoor concentrations of radon isotopes and progeny in indoor air can be viewed as a function of their outdoor concentration, the rate of emanation from inside, ventilation, deposition, and resuspension. Steady-state and time-dependent equations, derived by Thompson, were used to evaluate the relative effects of these variables on the potential alpha energy concentraiton (PAEC). Steady-state equations showed that at higher ventilation rates PAEC reduction of radon (Rn) is influenced more by ventilation than by progeny deposition, and at medium and higher deposition rates, the PAEC reduction of thoron (Tn) is affected little by ventilation. Calculations also show that the PAEC (Tn):PAEC (Rn) ratio increases, decreases, or remains constant, depending upon the ventilation rate. Calculations using the time-dependent equations showed that steady-state behavior was attained in 3 to 6 hours. The PAEC (Tn):PAEC (Rn) ratio, for time equal to 3 to 6 hours, was also shown to increase, decrease, or remains constant, depending upon the ventilation rate. For times under 3 hours, the PAEC (Tn):PAEC (Rn) ratio was shown to decrease with increased ventilation