Are you asking for atmosphere or sky (or both)? For sky I'd try to use a photo as the background. I don't know much about actual atmospheric effects (eg, haze, fog, dust, etc) - in the past I've just faked it in photoshop rather than Maya.
Take a glance at my <a href="https://forums.simplymaya.com/showthread.php?s=&threadid=9428"><b>Porsche 959</b></a> WIP