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

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Abstract
The influence of hygroscopic growth within the human respiratory tract on the deposition of H2SO4 aerosols was investigated using an analytical model. Particles were assumed to reach their equilibrium size and density on entering the trachea from the nasal or oral pharyngeal compartments. Calculated data were used to describe equilibrium values for specified relative humidity conditions which simulated the atmosphere, inhalation exposure chambers and the lung. Theoretical equations were used to calculate aerosol deposition efficiencies within conducting airways of the tracheobronchial tree. Hygroscopic growth affected the total dose deposited and its regional distribution. For an inspiratory flow rate of 30 l/min, the total deposition efficiency of H2SO4-and-H2O droplets, resulting from water condensation on H2SO4 particles of initial geometric diameter (Do), was > inspired nonhygroscopic particles of identical aerodynamic diameter when Do > 0.1 .mu.m. The opposite was found when Do < 0.1 .mu.m. Effects of hygroscopic growth were explained in terms of the changing deposition efficiencies of the inertial impaction, sedimentation and diffusion mechanisms. Results implied that it was important that hygroscopic growth within the human respiratory tract be accounted for when assessing the potential health hazard of airborne particulate matter.

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