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Clearing the Air Asthma and Indoor Air Exposures (2000) / Chapter Skim
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Appendix A: Theoretical Considerations Relevant to the Influence of Ventilation and Air Cleaning on Exposures to Indoor-Generated Pollutants
Pages 409-414

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From page 409...
... £acC, (A1) where Gi is the indoor particle generation rate per unit volume, lo is the air exchange rate equal to the rate of outside air entry Q divided by the indoor air volume V, ci is the indoor particle concentration, Step is the particle deposition velocity, A is the indoor surface area, Qac is the rate of airflow through the air cleaner, and 409
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From page 410...
... For many gaseous pollutants, an identical mass balance equation applies, except that there is no size variation and the deposition velocity is zero for some nonreactive gases. However, Equation A1 does not apply when the steady-state indoor pollutant emission varies with the indoor air pollutant concentration the case for some volatile organic compounds (VOCs)
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From page 411...
... Time to Fall 1 m 0.2 2.2 x 1 o-6 5.3 day 0.5 l.Ox10-5 28h 1.0 3.5 x 10-5 7.9 h 5.0 7.8x10 - 21min 10 0.003 330 s 20 0.012 83 s 30 0.027 37 s 50 0.075 13 s Particles also collide with and deposit on indoor surfaces due to mechanisms other than gravitational settling, and the deposition rates may vary with indoor air velocities, turbulence intensity, and surface roughness. As larger particles are transported by indoor air motion, their momentum causes collisions with surfaces.
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From page 412...
... When particles collide with a surface, they usually adhere as a consequence of van der Waals forces, electrostatic forces, and surface tension of liquid aerosols. Adhesive forces increase in proportion to the first power of particle diameter (Hinds, 1982~.
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From page 413...
... The assumption of perfect mixing is another limitation of Equation A1. With imperfect mixing and a localized indoor particle source, the benefits of ventilation or air cleaning may be enhanced if the ventilation exhaust inlet or the inlet to the air cleaner is near the pollutant source (e.g., a kitchen range hood)
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From page 414...
... 1996. Personal exposure to airborne particles and metals: results from the Particle TEAM Study in Riverside, CA.
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Key Terms

  • indoor air
  • deposition velocities
  • deposition velocity
  • particle deposition
  • particle removal

  • imperfect mixing
  • indoor surfaces
  • mass balance
  • deposition rates
  • air cleaner

  • air cleaning
  • gravitational settling
  • indoor particles
  • particle concentrations
  • balance equation

  • electrostatic forces
  • exchange rate
  • removal efficiency
  • air velocities
  • air exchange

  • empirical data
  • indoor pollutant
  • generation rate
  • deposition coefficients
  • larger particles

  • indoor surface
  • pollutant removal
  • pollutant concentration
  • particle concentration
  • limited empirical


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