This is what I learned about sunsets. Clean air is perfect for the best sunsets.
Sunlight is composed of a spectrum of colors that ranges from violet and blue
at one end to orange and red on the other. At sunrise or sunset, sunlight takes a
much longer path through the atmosphere than during the middle part of the day.
More violet and blue light is scattered out of the beam along the way, and so the
light which reaches the human eye early or late in the day is reddened.
So the conclusion is that sunsets are red because the daytime sky is blue.
(Please don't ask me why the sky is blue.)