1. Bruker Instruments Incorporated, 15 Fortune Drive, Billerica, Massachusetts 01821, U.S.A. (T.J.J.); Bruker Analytische Meßtechnik, Wikingerstrasse 13, 76189-Karlsruhe, Germany (A.S., J.M.W.); and Max Planck Institute for Atmospheric Chemistry, Saarstrasse 23, 55122-Mainz, Germany (G. W.H.)