Abstract
Aerosols play a substantial role in determining the quality and potential health impacts of indoor air. However, understanding how they are measured, monitored, and mitigated starts with a basic understanding of how they behave. The term “aerosol” refers to a collection of liquid and/or solid particles suspended in a gas. Aerosol behavior is determined by the physics of the suspending gas and the suspended particles and interactions between them. Starting from kinetic theory, this chapter develops an understanding of basic properties of gas behavior and how this is connected to aerosol behavior. Properties of gases from molecular mean free path and viscosity to boundary layers, Reynolds number, laminar and turbulent flow, and flow stagnation are described. Building on these, the chapter explores how interactions between particles and a surrounding gas affect behavior under different conditions. Concepts that are relevant to understanding aerosol behavior within indoor environments are addressed, including definitions of diameter (including aerodynamic diameter), linear and curvilinear motion, particle mobility, relaxation time, stopping distance, and diffusion. The chapter is designed to provide an introduction to aerosol dynamics that will be helpful in addressing the behavior and potential impacts of aerosols within indoor environments.
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Abbreviations
- A :
-
Area [m2]
- B :
-
Particle mechanical mobility [m N−1 s−1]
- c :
-
Velocity [m/s]
- c x :
-
Velocity in the x-direction [m]
- c rms :
-
Root mean square velocity [m/s]
- \( \overline{c} \) :
-
Mean velocity [m/s]
- C :
-
Concentration (e.g., gas concentration) [concentration units/m3]
- C c :
-
Cunningham slip correction [dimensionless]
- C s :
-
Slip correction [dimensionless]
- C D :
-
Drag coefficient [dimensionless]
- D :
-
Diffusion coefficient [m2/s]
- d :
-
Particle diameter [m]
- d m :
-
Collision diameter [m]
- d ae :
-
Aerodynamic diameter [m]
- d e :
-
Equivalent diameter (diameter of sphere with same volume) [m]
- d s :
-
Stokes diameter [m]
- F :
-
Force [kg m/s2 or N]
- F D :
-
Drag force [kg m/s2 or N]
- g :
-
Gravity [9.81 m/s2]
- J :
-
Flux. Particles [#/m2/s]
- k :
-
Boltzmann constant [1.38 × 10−23 J/K]
- m :
-
Mass. Often of a single particle or molecule. [kg]
- N :
-
Number of molecules per unit volume (gas kinetics) [#/m3]
- n :
-
Number of moles of gas (gas kinetics) [mol]
- N a :
-
Avogadro’s number [6.022 × 1023 mol−1]
- n c :
-
Molecule collisions per second [#/s]
- P :
-
Pressure [N/m2 or Pa]
- R :
-
Gas constant [8.31 Pa m3/K mol]
- Re :
-
Reynolds number [dimensionless]
- R c :
-
Radius of curvature
- S :
-
Stopping distance [m]
- Stk :
-
Stokes number [dimensionless]
- t :
-
Time [s]
- τ :
-
Relaxation time [s]
- T :
-
Temperature [K]
- U :
-
Velocity. Usually free stream gas
- V :
-
Volume [m3]
- V 0 :
-
Initial velocity [m/s]
- V T :
-
Terminal velocity [m/s]
- V TS :
-
Settling velocity [m/s]
- Vth :
-
Thermophoretic deposition velocity [m]
- x rms :
-
Root mean square distance traveled [m]
- η :
-
Viscosity [kg m−1 s−1]
- λ :
-
Mean free path [m]
- λp :
-
Particle mean free path [m]
- λ g :
-
Gas mean free path [m]
- ρ :
-
Density [kg/m3]
- ρ g :
-
Gas density [kg/m3]
- ρ p :
-
Particle density [kg/m3]
- ρ 0 :
-
Unit density [1000 kg/m3]
- χ :
-
Dynamic shape correction factor
References
Cunningham E (1910) On the velocity of steady fall of spherical particles through fluid medium. Proc Roy Soc London 83:357–365
Davies CN (1945) Definitive equations for the fluid resistance of spheres. Proc Phys Soc 57:259–270
Friedlander SF (2000) Smoke, dust, and haze: fundamentals of aerosol dynamics, Topics in chemical engineering, 2nd edn. Oxford University Press, Oxford, UK
Hinds WC, Zhu Y (2022) Aerosol technology: properties, behavior, and measurement of airborne particles, 3rd edn. Wiley, New York
Loeb LB (1961) The kinetic theory of gases. Dover Publication, New York, p 326
Ramamurthi M, Hopke PK (1989) On improving the validity of wire screen “unattached” fraction Rn daughter measurements. Health Phys 56:189–194
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Maynard, A., Hopke, P.K. (2021). Introduction to Aerosol Dynamics. In: Zhang, Y., Hopke, P.K., Mandin, C. (eds) Handbook of Indoor Air Quality. Springer, Singapore. https://doi.org/10.1007/978-981-10-5155-5_78-1
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DOI: https://doi.org/10.1007/978-981-10-5155-5_78-1
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