Modeling of atmospheric radon transport in East Asian region

A 222Rn monitoring network covering Japan, China and Korea has been in operation and hourly surface air concentration data have been obtained at more than ten stations since 2001. The data, especially those observed on small solitary islands were used to assess performance of a regional atmospheric transport model, which consists of the meteorological model MM5 and a 222Rn-210Pb transport model. The model successfully simulated large variations in concentration with several-day cycles observed during warm seasons from spring to autumn. However, the model systematically underestimated surface concentrations in winter. Considerations on spatial distribution of radon exhalation rate showed that the radon source strength used in this model simulation was still larger than conventional values or the distribution calculated by our new radon exhalation model. The use of these smaller exhalation rates will cause further underestimation by the atmospheric transport model. The most probable cause of this tendency of underestimation is the limitation of the turbulence model which might overestimate the diffusivity in and above the boundary layer. (author)