Mechanisms of Particle Deposition - Aerosols: Measurement, Dosimetry, and Health Effects - page 47

3 Mechanisms of Particle

Deposition*

Jacky A. Rosati, Kristin K. Isaacs, and Ted B. Martonen

CONTENTS
3.1 Introduction ............................................................................................................................ 48
3.2 Fundamentals of Inhaled Aerosols ......................................................................................... 48
3.2.1 Stokes's Law ............................................................................................................... 48
3.2.2 Terminal Settling Velocity and Relaxation Time ....................................................... 48
3.2.3 Aerodynamic Diameter .............................................................................................. 49
3.2.4 Modiications to the Aerodynamic Equations ............................................................ 49
3.2.4.1 Correction for Nonspherical Particles ......................................................... 49
3.2.4.2 Correction for Slip ....................................................................................... 50
3.2.5 Hygroscopicity ............................................................................................................ 52
3.3 Domains of Particle Dynamics............................................................................................... 53
3.3.1 Free-Molecule Regime ............................................................................................... 53
3.3.2 Continuum Regime..................................................................................................... 54
3.3.3 Slip-Flow Regime ....................................................................................................... 54
3.4 Inhalability.............................................................................................................................. 54
3.5 Deposition in the Extrathoracic Region.................................................................................. 55
3.6 Fluid Dynamics in Airways.................................................................................................... 55
3.6.1 Fundamentals of Flow ................................................................................................ 56
3.6.1.1 Steady versus Unsteady Flow ...................................................................... 56
3.6.1.2 Laminar versus Turbulent Flow................................................................... 56
3.6.2 Flow in Idealized Tubes.............................................................................................. 56
3.6.3 Flow in Curved Tubes................................................................................................. 58
3.6.4 Flow in Bifurcations and Branching Networks .......................................................... 59
3.7 Particle Motion ....................................................................................................................... 60
3.7.1 Primary Deposition Mechanisms ............................................................................... 60
3.7.1.1 Inertial Impaction ........................................................................................ 60
3.7.1.2 Sedimentation .............................................................................................. 62
3.7.1.3 Diffusion ...................................................................................................... 62
3.7.2 Secondary Deposition Mechanisms ........................................................................... 63
3.7.2.1 Interception .................................................................................................. 63
3.7.2.2 Electrostatic Charge..................................................................................... 65
3.7.2.3 Cloud Motion ............................................................................................... 66
3.8 Conclusions............................................................................................................................. 67
Nomenclature ................................................................................................................................... 67
References........................................................................................................................................ 69

* This chapter has been subject to an administrative review but does not necessarily relect the views of the EPA. No ofi-
cial endorsement should be inferred. EPA does not endorse the purchase or sale of any commercial products or services.

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