The last I heard of a 16km Atmosphere with fog was this file:
atompshere 16Km_scene.dat_file_Fog_Fixed.rar
do a forum search for the link, or i can email it to you if you need.
To edit the scene.dat the easiest way is Time Traveller's mini tweaker.
get it here:
http://www.delraydepot.com/tt/sh3.htm