ABSTRACT
The transport and deposition of aerosol particles in the respiratory tract is primarily determined by their physical characteristics (e.g., size, shape, and density) and the surrounding carrier airow patterns. Large and/or dense aerosol particles (e.g., micron-size and/ or heavy particles) tend not to follow the patterns of the carrier airows owing to a combination of their large inertia and the effect of gravity; thus, they deviate from the airow streamlines and deposit onto the airway surface. Inertia-driven deposition is called inertial impaction, whereas deposition due to gravity is called gravitational sedimentation. Smaller and/or lighter particles, such as nano-size particles (NPs) or ultrane particles (UFPs), have negligible inertia; thus, they cannot deposit by inertial impaction or gravitational sedimentation. It is, however, known that such particles do deposit; hence, they must do so by some other means.
