Modeling the dose distribution of H2SO4 aerosols in the human tracheobronchial tree

The influence of hygroscopic growth within the human respiratory tract upon the deposition of H2SO4 aerosols is investigated using an analytical model. Particles are assumed to reach their equilibrium size and density upon entering the trachea from either the nasal or oral pharyngeal compartments. Calculated data are used to describe the equilibrium values for specified relative humidity conditions which simulate the atmosphere, inhalation exposure chambers, and the lung. Theoretical equations are used to calculate aerosol deposition efficiencies within conducting airways of the tracheobronchial tree. Hygroscopic growth is shown to affect both the total dose deposited and its regional distribution. For an inspiratory flow rate of 30 L min-1, the total deposition efficiency of H2SO4-and-H2O droplets, resulting from water condensation upon H2SO4 particles of initial geometric diameter D0, is greater than inspired nonhygroscopic particles of identical aerodynamic diameter when D0 greater than 0.1 mu m. The opposite is found when D0 less than 0.1 mu m. The effects of hygroscopic growth are explained in terms of the changing deposition efficiencies of the inertial impaction, sedimentation and diffusion mechanisms. Results imply that it is important that hygroscopic growth within the human respiratory tract be accounted for when assessing the potential health hazard of airborne particulate matter.