A Dimensionless Measure of Filter Selectivity: Geometrical Factors in Cigaret Construction which Influence this Measure

A rational definition for characterizing the capacity of a cigarette filter to selectively modify the chemical composition of mainstream smoke is presented. The definition is related to the concept of separation factor as defined in chemical engineering and applied in the description of various unit processes. A number of numerical values for a wide range of cigarette filters currently found in the world market place are presented. The relative independence of the selectivity as defined in this paper upon tobacco types is demonstrated. Using a fixed filter construction in terms of amount and type of cellulose acetate fiber and plasticizer content, selectivity values are presented as a function of cigarette length and relative proportion of the cigarette which is allotted to the filter. Further, it is shown that selectivity appears to increase with length for given filter construction parameters. A limited amount of data regarding selectivity for weak acid components of mainstream smoke and certain gas phase components is presented as a characterization of dual filters currently on the US market