1. Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado 80309-0216, Department of Atmospheric and Oceanic Science, University of Colorado, Boulder, Colorado 80309-0311, Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, Aerodyne Research Incorporated, Billerica, Massachusetts 01821, and Tofwerk AG, Thun, Switzerland