Why is morning light so hard and cold and evening light so warm and soft?

I can think of a couple of reasons why the light at sunrise might be different at the light at sunset.

  1. 1.Anthropogenic effects. At the end of the day the cars and cooking fires and smokestacks have been going for a while, more so than at the end of the night. So sunsets might be different from sunrises because we behave differently during the day than at night.

  2. 2.Solar heating effects. At the end of the day the sun has been heating the ground and air all day. It seems plausible to me that higher temperatures would lift more tiny particles higher into the air, where they would cause more light scattering.