orange/red sunsets in a clean atmosphere

• created by rayleigh scattering
• at mid day, only a bit of the short wavelengths of visible light are scattered since the radiation is passing through a small distance in the atmosphere.
• at sunset, however, the radiation must pass through a much thicker layer of the atmosphere
• when the sun is at an angle of 4° from horizontal, the atmosphere appears to be 12 times thicker than at midday
• hence, much more blue light, and some green light are scattered
• therefore, the sun appears to look orange/red.
• this is for the case when the atmosphere is relatively clean, how will a sunset look when it is polluted?????