Deposition of combustion aerosols in the human respiratory tract: comparison of theoretical predictions with experimental data considering nonspherical shape.

Total deposition of petrol and diesel combustion aerosols and environmental tobacco smoke (ETS) particles in the human respiratory tract for nasal breathing conditions was computed for 14 nonsmoking volunteers, considering the specific pulmonary function parameters of each volunteer and the specific size distribution for each inhalation experiment. Theoretical predictions were 34.6% for petrol smoke, 24.0% for diesel smoke, and 18.5% for ETS particles. Compared to the experimental results, predicted deposition values were consistently smaller than the measured data (41.4% for petrol smoke, 29.6% for diesel smoke, and 36.2% for ETS particles). The apparent discrepancy between experimental data on total deposition and modeling results may be reconciled by considering the nonspherical shape of the test aerosols by diameter-dependent dynamic shape factors to account for differences between mobility-equivalent and volume-equivalent or thermodynamic diameters. While the application of dynamic shape factors is able to explain the observed differences for petrol and diesel combustion particles, additional mechanisms may be required for ETS particle deposition, such as the size reduction upon inspiration by evaporation of volatile compounds and/or condensation-induced restructuring, and, possibly, electrical charge effects.