1. Department of Meteorology, Pennsylvania State University, University Park, PA 16802
2. Department of Chemistry and Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138
3. National Oceanic and Atmospheric Administration (NOAA), Aeronomy Laboratory, Boulder, CO 80303
4. The Department of Chemistry, University of Cambridge, Cambridge, CB2 lEW, United Kingdom
5. The Atmospheric Chemistry Group, United Kingdom Meteorological Office, Bracknell, Berkshire, RG12 ZSZ, United Kingdom
6. At the National Aeronautics and Space Administration (NASA) Langley Research Center, Mail Stop 475, Hampton, VA 23665