Abstract
Inhaled submicron aerosols deeply reach into the human respiratory tract. The regional deposition in the bronchi and alveolar widely ranges from 70% for diameters of approximately 10 nm, 10–20% for 100 nm–1 μm, and almost 0% for larger than 10 μm (adult, male, nasal inhalation, and light exercising case). It also varies depending on the hygroscopicity because the respiratory tract below the larynx (bronchi and alveolar) is saturated with water vapor. Combustion-generated soot is generally hydrophobic when emitted (fresh soot), but condensation of the hygroscopic components on soot during long-range transport makes the soot larger and more hygroscopic (aged soot), and thus the regional deposition becomes smaller. Given the typical size and hygroscopicity for fresh soot and aged soot, the regional deposition of fresh soot is approximately twice that of aged soot. The regional deposition ranges for approximately ten-fold from 4.00 to 42.0% for the number equivalent geometric mean dry diameters of 40–280 nm, standard deviations of 1.3–2.0, and hygroscopicity κ of 0–0.7. Accurate assessment of the exposure to hazardous aerosol components requires identification of the host aerosol particles, which carry the hazardous components, and understanding of the host aerosols' size distribution and hygroscopicity, in addition to the bulk mass concentration of the aerosols and the hazardous components.
