1. Earth System Research Laboratory, Chemical Sciences Division, National Oceanic and Atmospheric Administration, 325 Broadway, Boulder, CO 80305‐3328 (USA), Fax: (+1) 303 497 5373
2. Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309 (USA)
3. Ecole des Mines de Douai, Département Chimie et Environnement, 941 rue Charles Bourseul, BP 10838, 59508 Douai cedex (France)
4. Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602 (USA)