Computation of ammonium bisulfate aerosol deposition in conducting airways

Experimental measurements of the growth of monodisperse dry NH4HSO4 aerosols by H2O vapor condensation have been reported in the literature. These data are incorporated into an aerosol deposition model to study the behavior of inhaled NH4HSO4 particles, which is of concern in relation to human health. The tracheobronchial tree is described by Weibel's model A morphology, and Landahl's formulas are used to compute particle deposition efficiencies. Enhanced losses in the trachea due to the action of the laryngeal jet are accounted for by using an empirical deposition efficiency equation. The effect of NH4HSO4 aerosol growth is quantitated by comparisons of total and intrabronchial deposition probabilities with those of a nonhygroscopic aerosol of equal aerodynamic size. Computations indicate that hygroscopic growth effects are a function of the size of the particles inhaled. Total deposition efficiencies of NH4HSO4-H2O droplet aerosols are greater than those of nonhygroscopic aerosols only if the former originate from dry NH4HSO4 particles exceeding a critical geometric diamter of 0.3 micrometer. Growth effects are explained in terms of the relative efficiencies of the dominant deposition mechanisms active in the lung.