The time variations of 222Rn were calculated using a local three-dimensional atmospheric dispersion model. The contribution of 222Rn emanated from at area near the measuring site to diurnal variations was estimated. The effects of a complex terrain were considered in this model. Some numerical analysis conducted in this study indicated that 222Rn emanated within a 40-kilometer circle around the objective point mainly contributes to diurnal variation of concentrations at the point. Simulated results considering the horizontal distribution of exhalation rate showed better coincidence with the observed results, compared with the results assuming a homogeneous exhalation rate. Model results were compared with three series of observed data of 222Rn concentrations at a height of 1m above the ground at Nagoya University. The variations of calculated and observed 222Rn concentrations were in good agreement.
