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ICRP 66 Lung Deposition Model

ICRP (International Commission on Radiological Protection) Publication 66 provides a human respiratory tract aerosol deposition model for evaluating health effects of inhaled particles.

Respiratory Tract Regions

Head Airways (HA)

  • Nasal cavity, pharynx, larynx
  • Primary mechanisms: Inertial impaction, gravitational settling
  • Main deposition region for large particles (>10 um)

Tracheobronchial (TB)

  • Trachea to terminal bronchioles
  • Mucociliary clearance mechanism
  • Deposition region for medium-sized particles

Alveolar (AL)

  • Respiratory bronchioles, alveolar ducts, alveoli
  • Gas exchange region
  • Main deposition region for fine particles (<1 um)

Deposition Mechanisms

Impaction

Large particles cannot follow airflow turns due to inertia and impact airway walls.

\[Stk = \frac{\rho_p D_p^2 U C_c}{18 \mu d}\]

Sedimentation

Particles settle on airway walls due to gravity, primarily in small airways and alveoli.

\[v_s = \frac{\rho_p D_p^2 g C_c}{18 \mu}\]

Diffusion

Ultrafine particles reach airway walls through Brownian motion.

\[D = \frac{k_B T C_c}{3 \pi \mu D_p}\]

Activity Level Parameters

Activity Breathing Rate (min-1) Tidal Volume (L) Ventilation (L/min) Breathing Mode
Sleep 12 0.625 7.5 Nasal
Sitting 12 0.75 9 Nasal
Light Activity 20 1.25 25 Mixed
Heavy Activity 26 1.92 50 Oral

Deposition Fraction Curve

The relationship between particle size and total deposition efficiency shows a U-shape:

  • Ultrafine particles (<0.1 um): Diffusion dominated, high deposition efficiency
  • Accumulation mode (0.1-1 um): Lowest deposition efficiency ("penetration window")
  • Coarse particles (>1 um): Impaction and sedimentation dominated, high deposition efficiency

AeroViz Implementation

from AeroViz.dataProcess.SizeDistr import SizeDist

# Create PSD object
psd = SizeDist(df_pnsd, state='dlogdp', weighting='n')

# Calculate lung deposition
result = psd.lung_deposition(activity='light')

# Output
result['DF']         # Deposition fraction DataFrame (HA, TB, AL, Total)
result['deposited']  # Deposited distribution (dN/dlogDp x DF)
result['dose']       # Regional dose
result['total_dose'] # Total deposited dose

Output Example

# Deposition fractions (by particle size)
result['DF']
#           HA       TB       AL    Total
# 11.8   0.012    0.045    0.285    0.342
# 20.5   0.008    0.032    0.198    0.238
# 50.0   0.005    0.018    0.112    0.135
# 100    0.004    0.012    0.085    0.101
# 200    0.006    0.015    0.095    0.116
# 500    0.025    0.035    0.125    0.185

Health Significance

  • HA deposition: Primarily cleared by mucociliary system
  • TB deposition: May cause bronchitis, asthma
  • AL deposition: Particles may enter bloodstream, affecting cardiovascular system

References

  1. ICRP (1994). Human Respiratory Tract Model for Radiological Protection. ICRP Publication 66, Ann. ICRP 24(1-3).
  2. Hinds, W. C. (1999). Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles. Wiley.