1. Earth System Research Laboratory, Chemical Sciences Division, National Oceanic and Atmospheric Administration, 325 Broadway, Boulder, Colorado 80305-3328, United States
2. Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309, United States
3. Department of Chemistry, University of North Texas, P.O. Box 305070, Denton, Texas 76203-5070, United States
4. DuPont Central R&D, Wilmington, Delaware 19880, United States