1. Polarization via Rayleigh Scattering
A wave packet incident on a small particle (<l/15) causes electron oscillations, creating a dipole.
As a result, light is re-emitted in a random direction, but polarized parallel to the dipole oscillation axis.
In this way, the incoming light undergoes the maximum polarization at 90° from the angle of incidence.
Atoms and molecules in the upper atmosphere are <1nm in size, so they can scatter light in the visible spectrum (~400nm<l<~700nm)
The intensity of the scattered light increases with with (1/l)4, so the intensity of blue light scattered by the atmosphere is much greater than that of red light.
Therefore, we have blue skies, red sunsets, and polarized light 90° from the sun.