Aerosol science is the rapidly expanding field of science which investigates the physical, chemical, and biological properties of aerosolized materials (airborne particles), which behave in ways that make them unique from even other forms of similar materials. Of particular interest are their measurement; methods of formation, transport and deposition; and applications in medicine, industry, and environmental science. ^[1]

Single Particle Characterization

Size Distribution

Aerosols are characterized by a particle size distribution function (PSD). Most natural aerosols have a lognormal distribution.

Shape and Fractal

Almost all the solid particles are not spherical.

Aerosol Physics

Aerosol Mechanics

• Equation of Motion

m \frac{du^p}{dt}= \frac{3\pi \mu d}{Cc} (u^f-u^p)+ mg

where

\ u^p is particle velocity

\ u^f is fluid velocity

\ \mu is fluid viscosity

\ m is the mass of particle

\ d is particle diameter

\ g is the acceleration of gravity

\ Cc is Cunningham correction factor

Here, the buoyancy of air is neglected and Stokes drag is assumed.

• Particle relaxation time
• Particle stopping distance
• Brownian motion or Diffusion

Aerosol Dynamics

Aerosol dynamics is focus on the evolution of aerosol population.

Aerosol population is characterized by a particle size distribution function (PSD). Most natural aerosols have a lognormal distribution.

Aerosol formation and growth consists of 3 processes:

1. Nucleation
2. Coagulation/Agglomeration
3. Condensation

Aerosol dynamics is characterized by a single differential equation called as the Aerosol General Dynamic Equation (GDE).

\frac{\partial{N_k}}{\partial{t}}+\nabla.n_kv=\nabla.D\nabla_k+ \left[\frac{\partial{n_k}}{\partial{t}}\right]_{growth}+ \left[\frac{\partial{n_k}}{\partial{t}}\right]_{coagulation} -\nabla.cn_k

where J is the nucleation rate, \beta is the coagulation kernel and G is the growth rate.

The common methods to solve the GDE are:

1. Moment method
2. Modal/Sectional Method
3. Quadrature Method of Moments.

Nucleation

Nucleation is the process of forming particles from a purely gaseous precursor phase.

There are two types of nucleation processes,

1. homogenous nucleation
2. heterogeneous nucleation.

Nucleation occurs for different reasons. Important among them, is the supersaturation of a vapor. When a hot vapor in a gas is cooled down, its supersaturation ratio increases, and it becomes supersaturated. Therefore, it "precipitates out" into particles. This process is called nucleation.

Coagulation

When particles are present in an aerosol they collide with each other. During that they may undergo coalescence or aggregation. This process leads to a change in the aerosol size distribution function.

Condensation

Condensation is the process by which an aerosol particle grows with the accretion of monomers or individual molecules to an already existent particle.

Aerosol Generation and Detection

Generation Instruments

• Atomizer nozzle or Nebulizer
• Electrospray
• Vibrating Orifice Aerosol Generator (VOAG)

Detection Instruments

• Aerosol Mass Spectrometer (AMS)
• Differential Mobility Analyzer (DMA)
• Aerodynamic Particle Sizer (APS)
• Wide Range Particle Spectrometer (WPS)
• Micro-Orifice Uniform Deposit Impactor(MOUDI)
• Condensation Particle Counter (CPC)

See Also

• Aerosol
• Particulate

Notes

• William C. Hinds, Aerosol Technology, 2nd ed., John Wiley & Sons, ISBN 0-471-19410-7.
• Sheldon K.Friedlander, Smoke, Dust and Haze, 2nd ed., Oxford University Press, ISBN 0-19-5129, 99-7.
• Kulkarni, Pramod; Baron, Paul A.; Willeke, Klaus, ''Aerosol Measurement - Principles, Techniques, and Applications,'' 2011 John Wiley & Sons, ISBN 978-0-470-38741-2.
• Preining, Othmar and E. James Davis (eds.), History of Aerosol Science, sterreichische Akademie der Wissenschaften, ISBN 3-7001-2915-7 (pbk.)
• Aerosol Education Resources

References

fi:Aerosolifysiikka