Calculation of Total Deposition Fraction of Ultrafine Aerosols in Human Extrathoracic and Intrathoracic Regions

Total deposition fraction during inspiration and expiration can be considered as an index of cumulative doses of inhaled particles. We have calculated the total deposition fraction of ultrafine aerosols for the 5–200-nm-diameter range in the extrathoracic and intrathoracic airways for two breathing rates, 7.5 and 15 L min−1, based on the total respiratory deposition measurements of Schiller et al. (1988) and the empirical extrathoracic aerosol deposition equations of Cheng et al. (1993) and Swift et al. (1993). Our results indicate that extrathoracic particle deposition during expiration is an important component of total extrathoracic deposition fraction for particle diameters less than 20 nm. The intrathoracic deposition fraction increases as particle diameter increases from 5 to 20 nm, and decreases with increasing particle diameter from 20 to 200 nm. These trends were observed for both oral and nasal breathing for both respiratory flow rates.