What is the best way to add considerable fog?

[RideTheCatfish]

I don't have a god computer - it can run the game on high, but things still look absolutely terrible in the distance. Things are jumpy, fading in and out of view, positively mangeled. It kills the immersion for me, really depreciates the atmosphere.

 

So I tried depth of view and I tried motion blur and nothing there really worked. So now I've decided to move onto what seems to be my only course of action - added considerable fog so things seem "dusty" and things and a great distance hardly appear at all. I won't get the grand view of the Mojave, but 'a grand view of the Mojave' is like a bit like the grand view of a dirty public restroom.

 

Now I ask you all - what would be the easiest way to do this? Is there a way I can do it without going into every weater type and changing the fog? That would be easy enough, I know, but there's always the chance of screwing things up, and imagespace modifiers often seem to negate things like fog...