Aerosols of smoke, respiratory physiology and deposition.

Tobacco smoke is discussed as a multi-component droplet aerosol system of finite airborne life time which changes rapidly right after formation near the combustion zone of the tobacco and continues to change gradually when aging and approaching a multiphase steady state between vaporized smoke constituents mixed into the air and the dispersed particulate phase which will eventually vanish because of physical mechanisms removing the smoke particles from the airborne state. Data on chemical composition and physical characteristics of mainstream and sidestream cigarette smoke are compared and the dynamic models of aerosol particle behavior and deposition in the respiratory tract under different physiological conditions are discussed. While differences in chemical composition between mainstream and sidestream smoke aerosol systems are reported in the literature at least for the gas phase, there seems to be no reliable body of evidence confirming that mainstream and sidestream cigarette smokes have sufficiently different physical characteristics which would cause substantially different deposition patterns and different relative deposition in the respiratory tract. However, there are scanty experimental data in the literature on cigarette smoke deposition in the lung which seem to indicate that mainstream smoke deposition may exceed theoretical expectations while sidestream smoke may not. Further experimental results are needed before firm conclusions can be drawn. An ongoing experimental effort is described where deposition of sidestream cigarette smoke will be measured on mouth breathing test panels.