Influence of desorption on the indoor concentration of toxic gases

Abstract A theoretical model is developed which considers the influence of both deposition and desorption processes on the indoor concentration of toxic gases. The model is based on a simplification of the Langmuir theory. Model parameters for NH 3 , Cl 2 , the nerve agent sarin, and a simulant for the nerve agent VX are calculated from available experiments with common indoor materials. The adaptation of parameters seems to work well for low to moderate exposure. The model is then used to study concentrations of the nerve agent sarin in ordinary buildings after a hypothetical attack. Desorption results in a residual indoor concentration over an extended period, and, in contrast to a non-desorbing gas, the indoor exposure ∫ τ 0 c i d t of a desorbing gas can therefore approach the outdoor exposure given sufficient time. For several indoor materials this approach is slow, especially under conditions of low ventilation. A very high deposition and a low desorption of sarin to/from unpainted concrete is found, thus demonstrating that rooms of unpainted concrete offers good protection against sarin.