Department of Chemistry, University of California Berkeley, Berkeley, CA, USA

Department of Earth and Planetary Science, University of California Berkeley, Berkeley, CA, USA

now at: NOAA Earth System Research Laboratory and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, USA

Department of Chemistry, University of California Berkeley, Berkeley, CA, USA

Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA

Department of Chemistry, University of California Irvine, Irvine, CA, USA

Department of Meteorology, Pennsylvania State University, University Park, PA, USA

Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA

Cooperative Institute for Research in the Environmental Sciences (CIRES) and Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA

now at: Tofwerk AG, Thun, Switzerland

NASA Langley Research Center, Hampton, Virginia, USA

Cooperative Institute for Research in the Environmental Sciences (CIRES) and Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA

Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA

Division of Geology and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA

Institut für Ionenphysik & Angewandte Physik, University of Innsbruck, Innsbruck, Austria

Department of Chemistry, University of California Berkeley, Berkeley, CA, USA

Department of Earth and Planetary Science, University of California Berkeley, Berkeley, CA, USA