Aerosol science


Aerosol science

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

Aerosol formation and growth consists of 3 processes:

# Nucleation
# Coagulation/Agglomeration
# Surface Growth

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

frac{partial{N_k{partial{t+ abla.n_kv= abla.D abla_k+ left [frac{partial{n_k{partial{t ight] _{growth}+ left [frac{partial{n_k{partial{t ight] _{coagulation} - abla.cn_k

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

The common methods to solve the GDE are:

# Moment method
# Modal/Sectional Method
# 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,
# homogenous nucleation
# 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.

Surface Growth

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

References

* 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 0-19-512999-7.
* Preining, Othmar and E. James Davis (eds.), "History of Aerosol Science," Österreichische Akademie der Wissenschaften, ISBN 3-7001-2915-7 (pbk.)


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