[1] Univ Denver, Dept Phys, Denver, CO 80208 USA
[2] Univ Massachusetts, Dept Environm Earth & Atmospher Sci, Lowell, MA 01854 USA
[3] Univ Paris Sud, Photophys Mol Lab, F-91405 Orsay, France
[4] NASA, Div Atmospher Sci, Langley Res Ctr, Hampton, VA 23681 USA
[5] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA