Estimation of seasonal variations in 222Rn from different origins using the correlation between 222Rn and 212Pb concentrations in air. 2. Simulation of atmospheric 222Rn concentrations from distant regions using the box model

The concentration of 222Rn originating from distant regions was simulated using the box model for 222Rn(T1/2 = 3.82d) and 212Pb(T1/2 = 10.6 h) in outdoor air. The representative values of some parameters causing change in 222Rn concentration were estimated and compared with the concentration of 222Rn from distant regions obtained by the method described in the previous report. The main results are as follows: 1) The exhalation rate for 222Rn was about 5 mBq.m-2.s-1 near the measuring site. 2) The values of exhalation rate for 220Rn varied from 30-180 mBq.m-2.s-1 over 2 years. The variation can be partly explained by three factors, namely, soil moisture, atmospheric pressure, and wind speed. 3) The height of the inversion layer was lower in winter. (author)