[chris (OP)]

As the Sun sets, the light we see appears redder because the light path through the atmosphere becomes longer which leads to a great degree of scattering of the shorter wavelengths. Pollution is said to intensify the sunset effect. Presumably the pollution particles, being even larger than the atmospheric gas molecules, scatter even longer wavelengths of light to shift the colour even more towards the red? But is there not also the possibility that the particles scatter red light itself? This would have an effect similar to the impact of nitrogen and oxygen making the sky look blue...