Page 264 - Industrial Ventilation Design Guidebook

5,2 HUMAN RESPIRATORY TRACT PHYSIOLOGY 225

FIGURE 5.28 Estimated overall airway deposition as a function of initial particle size and parti-
cle hygroscopicity for particles with mass median aerodynamic diameters (MMAD) between 0.1 and
10 (Jim. 102 Geometric dispersion, a measure of particle size distribution, principally affects only
smaller MMAD.

Consequently, any breathing pattern which increases pulmonary residence
times, such as breath-holding, increases fine particle deposition throughout
the airway.
Where along the airway inspired particles deposit depends on particle
mass, since the deposition mechanism depends on particle MMAD. Passage
through the airway has no effect on nonhygroscopic particle mass (e.g., fly
ash), and initial MMAD determines the deposition pattern (Fig. 5.28), In con-
trast, hygroscopic particles (e.g., acid droplets) increase in mass when exposed
to humid environments like the respiratory tract. Particle properties (e.g.,
chemical composition, ionic concentration, and particle surface area) and air-
stream conditions (e.g., temperature, RH, and V E) which affect hygroscopic
growth consequently play major roles in determining particle mass and depo-
sition patterns (Fig. 5.29).
Acid Aerosol Neutralization
Sulfuric acid (H 2SO 4) and ammonium bisulfate (NH 4HSO 4) contribute im-
portantly to ambient acid aerosols, particularly in geographic locations where
sulfur-rich coal is used for power plant fuel, such as the eastern United
103
States. Studies on animals and human subjects have shown that H 2SO 4 and
104 106
NH 4HSO 4 alter mucociliary transport in a dose-dependent fashion " and
can adversely affect pulmonary function in humans. 106 While this effect on
clearance has generally been attributed to hydrogen ion concentration, [H+], the
+
work of Schlesinger et al. 107 suggests that, for equivalent inhaled [H ], H 2SO 4
elicits a greater change than NH 4HSO 4. If this observation is confirmed, it