The objective of this work is to model the deposition of semivolatile aerosols in the lungs based on gas-particle and tissue-air partitioning theory. Semivolatile compounds exist in air as both particles and gases simultaneously. Mass distributes between the two phases according to a gas-particle partitioning ratio, R(pg) = K(p)(TSP). Particle deposition in the lungs is a function of aerodynamic diameter, whereas gas deposition is a function of tissue solubility, which is related to the air-lung partitioning ratio, K(la). Therefore, deposition to the lungs will vary with R(pg) and K(la). These and other parameters determine a dimensionless deposition number, D, which indicates whether particles or gases are most responsible for deposition of semivolatile chemicals in the lung. The deposition number allows industrial hygienists to design effective air sampling strategies and control measures that will minimize risks associated with exposure to semivolatiles. Examples of deposition numbers for common semivolatile pollutants are provided, including alkanes, polycyclic aromatic hydrocarbons, pesticides and polychlorinated biphenyls.
