Application of an equilibrium-based model for diffusion barrier charcoal canisters in a small volume non-steady state...

Radon in indoor air is often measured using activated charcoal in canisters. These are generally calibrated using large, humidity- and temperature-controlled radon chambers capable of maintaining a constant radon concentration over several days. Reliable and reproducible chambers are expensive and may be difficult to create and maintain. This study characterizes a small radon chamber in which Rn gas is allowed to build up over a period of several days for use in charcoal canister calibration and educational demonstrations, as well as various radon experiments using charcoal canisters. Predictive models have been developed that accurately describe radon gas kinetics in the charcoal canisters. Three models are available for kinetics in the small chamber with and without radon-adsorbing charcoal canisters. Presented here are both theoretical and semi-empirical applications of this equilibrium-based model of radon adsorption as applied to canisters in the small chamber. Several charcoal canister experiments in the small chamber with an equilibrium-based model of radon adsorption applied are reported. Results show that it is necessary to include a continuous radon monitor in the chamber during canister exposures, as the radon removal rate is highly variable. Furthermore, the presence of the canisters significantly decreases the amount of radon in the small chamber, especially when several canisters are present. It was found that canister response in the small chamber is largely consistent with the equilibrium-based model for both applications, with average errors of 1% for the theoretical application and -4% for the semi-empirical approach.