http://www.scribd.com/doc/7209289/course47Siggraph2001
Downloading it now, the scribd interface is a little slow for me. These things usually have some pretty good theories, although there haven't been many decent stuff recently. Most of what I've found after 2006 is more resource orientated, so anything to do with, say, lighting is pretty out of date. I found this though which is pretty cool, lots of info on atmospheric simulation. I have the complete paper on my computer but it's too big to upload.
http://www.ecn.purdue.edu/purpl/level2/papers/AMS84_riley.pdf