Estimation of 222Rn concentration originating from distant regions using the correlation between 222Rn and 212Pb concentrations in air

Continuous measurements of 222Rn (half-life is 3.82 days) and 212Pb (half-life is 10.6 hours) concentrations in outdoor air were carried out in Tokyo. Positive correlations were found between 222Rn and 212Pb concentrations. Using the intercept values obtained from the regression line, a new method was proposed for separating the seasonal variation of the monthly mean 222Rn concentration according to its origin. The reliability of the present method was verified by comparing the estimated concentrations of 222Rn originating from distant regions with the value calculated using the long-range transport model. The seasonal variations of the concentrations of 222Rn originating from distant regions and near the measuring site in Tokyo were investigated. It was founded that the seasonal variation of 222Rn concentration, which was high in winter and low in summer, was influenced by both components. (author)