Atmospheric Aerosol

:: Section 9

Visibility Effect of Atmospheric Aerosol

I. Light Extinction

The extinction (including scattering and absorption) of light is given by Bouguer's law (also known as Lambert-Beer law):

where:

I0 = incident light intensity; I = light intensity traversing the aerosol; σe = extinction coefficient of the aerosol; L = path length of the light through the aerosol

The following animation shows the process of light extinction by aerosols.

For a monodisperse aerosol, the extinction coefficient is:

where:

N = particle concentration (number per unit volume); Ap = cross-section area of a particle; d = particle diameter (assuming spherical particles); Qe = single particle extinction efficiency, which is a complex function of particle size and refractive index (Details for Q_e are available in the reference books listed)

For polydisperse aerosols, the above equation holds for each particle size, and the combined effect is given by the sum of the extinction coefficients for all the particle sizes.

	Definition
Monodisperse particles:		particles that have the same size
Polydisperse particles:		particles that have a size distribution