A theoretical model for 222Rn adsorption on activated charcoal canisters in humid air based on Polanyi's potential...

Water vapor interferes with the adsorption of 222Rn gas by passive activated charcoal devices used to estimate indoor air concentrations. The 222Rn adsorption coefficient is the fundamental parameter characterizing charcoal's ability to adsorb 222Rn. The Dubinin-Radushkevich equation, based on Polanyi's potential theory, was modified to include two terms quantifying the effect of both water vapor and sampling time on the 222Rn adsorption coefficient of passive charcoal devices. A single equation was derived that quantifies the 222Rn adsorption coefficients at any temperature, humidity and exposure time using six experimentally determined physical constants that are unique for a particular passive charcoal device. The theoretical model was verified with published experimental data, and it showed a good correlation between theory and experiment. The model proved to be consistent with experimental data, provided that the amount of water vapor adsorbed by the charcoal device during sampling remains below a critical level, termed the breakpoint.