Short-lived daughter ions of radon 222 in relation to some atmospheric processes

The behavior of 222Rn daughter ions in fair weather and thunderstorm environments has been investigated numerically. One-dimensional time-dependent differential equations for radioactive ions employed in the numerical model involve, in addition to the usual terms for radioactive decay and eddy diffusion, terms for ion attachment and recombination, electric field, and vertical wind. Numerical and experimental results are compared to show the applicability of the model to predictions of the behavior of 222Rn daughter ions in different atmospheric conditions. Eddy diffusion affects concentrations of both 222Rn and its daughter ions similarly and produces changes in their concentrations of the order of 10 in a diurnal period. Inclusion of the term for the vertical wind in the differential equations for both 222Rn and its daughter ions produces similar changes in both concentrations. In contrast to eddy diffusion and the vertical winds, attachment and ion migration due to electric fields such as those existing during thunderstorms affect solely the concentration of radioactive ions. These effects are shown to be the dominant ones under certain meteorological conditions. A change in the concentration of the condensation nuclei from 104 to 105 nuclei/cm3 increases ion attachment and causes a reduction by a factor of about 7 in the concentration of radioactive ions. Under thunderstorm conditions with E of the order of 100 volts/cm the reduction in ion concentration close to the ground is of the order of 8 or more, owing to upward migration of radioactive ions. The numerical solutions for radioactive ions show that the migration effect producing a decrease in the concentration of radioactive ions can be observed up to 50 meters above the ground, beyond which the concentrations approach the values for fair weather. The recombination effect is negligible, since a change in n− from 550 to 2750 ions/cm3 causes a decrease of only about 3% in the concentration of radioactive ions.