Mechanisms of Particle Deposition - Aerosols: Measurement, Dosimetry, and Health Effects - page 67

The requirement of V c ≫ V p led directly to the following criteria for the existence of cloud motion:

2

⎡
⎢

d
d

⎤
⎥

1
6

p

2 3 /

(3.45)

ρ ρ C ( 6 + Re )

c p c c

c

Therefore, cloud motion may be a factor in airway deposition when the mass concentration of
inhaled particles is very high.

3.8 CONCLUSIONS
The deposition of inhaled particles is a function of aerosol characteristics, ventilatory parame-
ters, and respiratory system morphologies. Deposition in human airways is especially linked to air
motion and luid dynamics. We have provided the fundamental theory behind many of the factors
that affect deposition, and have presented equations for the deposition eficiencies of several depo-
sition mechanisms under different low conditions. However, we stress that the many of the basic
formulae presented herein were derived for idealized or simpliied conditions. The formulation
of more advanced, simulation-based methods of predicting particle deposition in the respiratory
system are currently being developed. We will present an overview of these methods in Chapter V,
Modeling Particle Deposition.

NOMENCLATURE
Particle Quantities

d p particle diameter (μm)

d g geometric diameter (μm)

d ae aerodynamic diameter (μm)

V p particle velocity (cm·s −1 )

V TS particle terminal settling velocity (cm·s −1 )

ρ p particle mass density (g·cm −2 )

ρ u unit density (g·cm −2 )

m particle mass (g)

Π dynamic shape correction factor (dimensionless)

F D drag force on a particle (g·cm·s −2 )

τ relaxation time (s)

r g particle hygroscopic growth rate (μm·s −1 )

C c Cunningham slip correction factor (dimensionless)

D diffusion coeficient (cm 2 ·s −1 )

n molecular density (molecules·cm −3 )

d m molecular diameter (μm)

C D particle drag coeficient (dimensionless)

I inhalability ratio (dimensionless)

Air Characteristics

STP standard temperature and pressure:

T = 273 K (0°C)

P = 1 atm = 1.01 × 10 6 g·cm −1 ·s −2

μ absolute air viscosity (g·cm −1 ·s −1 ) at STP, μ = 1.82 × 10 −4 g·cm −1 ·s −1

ρ a air density (g·cm −3 ) at STP, ρ g = 1.2 × 10 −3 g·cm −3