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# 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:

1. Nucleation
2. Coagulation/Agglomeration
3. Surface Growth

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

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

where J is the nucleation rate, β 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

## 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.

## 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.)