Rayleigh Scattering - The scattering of light by a body with a particle diameter (D_p) less than 0.03 micrometers is termed Rayleigh Scattering. The wavelength of light scattered is dependent on the D_p, and the amount of light scattered is dependent on the number of particles present per unit volume. Shorter visible wavelengths, such as blue, are scattered by smaller particles than are the longer wavelengths like red.
[American Journal of Physics; v57; p552-3; 1989.]
[American Journal of Physics; v56; p948-50; 1988.] 
Atmospheric Chemistry Glossary