Rayleigh scattering
There are two kinds of light scattering that lead to sky glow: scattering from molecules such as N2 and O2 (called Rayleigh scattering), and that from aerosols, described by Mie theory. Rayleigh scattering is much stronger for short-wavelength (blue) light, while scattering from aerosols is less affected by wavelength. Rayleigh scattering makes the sky appear blue in the daytime; the more aerosols there are, the less blue or whiter the sky appears. In many areas, most particularly in urban areas, aerosol scattering dominates, due to the heavy aerosol loading caused by modern industrial activity, power generation, farming and transportation.