Development and Verification of Long-Range Atmospheric Radon-222 Transport Model

A three-dimensional Eulerian atmospheric long-range transport model of Rn-222 and Pb-210 coupled with meteorological model MM5 was developed. The transport model includes advection, diffusion and removal processes in a horizontal scale of several thousand kilometers. Performance of the developed model was evaluated with measured data of surface Rn-222 concentration and surface Pb-210 deposition. The refinements of calculation conditions and input data were also done with respect to the following points: 1) the sensitivity of spatial distribution of Rn-222 exhalation and 2) the accuracy of spatial distribution of precipitation. The model reasonably calculated the surface Rn-222 concentration at two solitary islands in Pacific Ocean. Introducing a realistic spatial distribution of Rn-222 exhalation rate, the calculated surface Rn-222 concentrations showed good agreement with measured concentration. The calculation of Pb-210 deposition was in quite good agreement with measurement if realistic precipitation distribution was used. These results show that the developed model can realistically calculate atmospheric transport Of Rn-222 and Pb-210 in a synoptic scale.