1. Th. Peter, C. Marcolli, P. Spichtinger, and T. Corti are at the Institute for Atmospheric and Climate Science, Eidgenössische Technische Hochschule (ETH) Zürich, 8092 Zürich, Switzerland.
2. M. B. Baker is in the Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195, USA.
3. T. Koop is in the Department of Chemistry, Bielefeld University, D-33615 Bielefeld, Germany.