1. Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado.
2. Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado.
3. Department of Atmospheric and Oceanic Sciences and Laboratory for Atmospheric and Space Physics, Boulder, Colorado.
4. Department of Planetary Sciences, Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona.
5. Space Science Division, NASA Ames Research Center, Moffett Field, California.