REMOVAL OF REACTIVE GASES AT INDOOR SURFACES - COMBINING MASS-TRANSPORT AND SURFACE KINETICS

The rate of deposition of reactive gaseous pollutants onto indoor surfaces is examined, taking into account mass transport processes and the kinetics of gas-surface interactions. A conceptual model for predicting indoor deposition velocities is proposed, and approximate analysis based on this model is used to obtain algebraic expressions for the deposition velocity of reactive gases under three model airflow conditions: (1) forced laminar convection parallel to a flat plate, (2) laminar natural convection flow along an isothermal vertical plate, and (3) homogeneous turbulence in an enclosure. Numerical simulations are used to refine the approximate analysis results and to predict reactive gas deposition under laminar natural convection flow in an enclosure. The kinetics of gas-surface interactions are modeled in terms of the reaction probability gamma, defined as the fraction of pollutant molecular collisions with a surface that result in irreversible removal. Values of gamma for the reaction of ozone with surfaces are obtained from published reaction chamber and tube penetration experiments. For common indoor materials, values range from as low as O(10(-7)) for glass and aluminium to O(10(-5)-10(-4)) for materials such as bricks, concrete and latex paint. Our results indicate that ozone deposition occurs at the transport-limited rate when gamma > approximately 3 x 10(-4) for typical indoor air flow conditions, and that ozone deposition can be predicted by surface kinetics alone if gamma < approximately 5 x 10(-7).