Why is the sky more red at sunset and more purple at sunrise?

Question

My guess is that is has something to do with warmer air by the end of the day and cooler air in the morning thus creating different densities and leves of atmospheric dust which refracts light. What's the real answer?

Answer 1

Something like that, although, the expectation is that human activity levels prior to sunrise and sunset are radically different, so you'd expect a radically different level of aerosols during sunrise and sunset.