1. Department of Atmospheric Sciences University of Washington Seattle WA USA
2. Now at Laboratory of Atmospheric Chemistry, Paul Scherrer Institute Villigen Switzerland
3. Department of Chemistry and Cooperative Institute for Research in Environmental Sciences University of Colorado Boulder Boulder CO USA
4. School of Earth and Atmospheric Sciences Georgia Institute of Technology Atlanta GA USA
5. Department of Atmospheric Science Colorado State University Fort Collins CO USA
6. Institute for the Study of Earth, Oceans, and Space University of New Hampshire Durham NH USA
7. National Center for Atmospheric Research Boulder CO USA
8. Chemical Sciences Division NOAA Earth System Research Laboratory Boulder CO USA