[en] The authors determined the contents of natural uranium and thorium in coal and tunnel ash samples taken from a large coal-fired power station in the nearby area. The hourly climate data in 1980 are analysed and the atmospheric stability is cataloged by Pasquill-Turner method. Wind direction-atmospheric stability-wind velocity combined probabilities and rain-wind direction probabilities are calculated. The near ground air pollution concentrations, the ground depositions and the distributions of U and Th presented in airborne effluent (fly ash) within an area round the station with a radius of 60 km are also estimated. In the calculations, some factors such as wind velocity in the higher atmosphere, plume rise, still wind and decrease of air pollution concentration by the ground deposition (especially the wet deposition porduced by rain) have been considered. Some corrections necessary for the factors described above are also made. It is shown that the maximum annual average air pollution concentration (U_max = 1.95 x 10^-7 mg.m^-3, Th_max = 3.45 x 10^-7 mg.m^-3) appears at the point 1 km away from the source in the fan SE. In the area round the station with a radius shorter than 10 km, the ground deposition is mainly by the wet deposition, but, where the radius longer than 10 km, the dry deposition must be taken into account