After a full day being warmed by Mr. Sun and thoroughly mixed by the accompanying winds, the atmosphere at sunset is a miasma of dust and smog. After a relatively calm night with fewer winds, the particulates will largely have settled out, yielding a much cleaner-looking atmosphere by sunrise.
You know that huge, bulbous, often slightly aspherical sun you sometimes see sitting low on the horizon? The kind that’s so filtered and dimmed by the roiled, hazy atmosphere that you can look right at it? That’s a dusk sun.
You know that seemingly much smaller but searingly bright ball slightly above the horizon that leaves you blinking reverse-image spots? The kind that seems so crystal clear in the instant before you’re temporarily blinded that you’d swear you could see a solar flare or two? That’s a dawn sun.