Validity of the uniform mixing assumption: Determining human exposure to environmental tobacco smoke

When using the mass balance equation to model indoor air quality, the prima ry assumption is that of uniform mixing. Different points in a single compa rtment are assumed to have the same instantaneous pollutant concentrations as all other points. Although such an assumption may be unrealistic, under certain conditions predictions (or measurements) of exposures at single poi nts in a room are still within acceptable limits of error (e.g., 10%). in t his article, three studies of the mixing of environmental tobacco smoke (ET S) pollutants are reviewed, and data from several other ETS field studies a re presented. Under typical conditions for both short sources (e.g., 10 min ) and the continuous sources of ETS in smoking lounges, I find that average exposure concentrations for a single point in a room represent the average exposure across all points in the room within 10% for averaging times rang ing from 12 to 80 min. I present a method for determining theoretical estim ates of acceptable averaging limes for a continuous point source.