1. Department of Atmospheric Sciences; University of Washington; Seattle WA USA
2. Chemical Sciences Division; Earth System Research Laboratory, National Oceanic and Atmospheric Administration; Boulder CO USA
3. Cooperative Institute for Research in Environmental Sciences; University of Colorado Boulder; Boulder CO USA
4. Department of Chemistry and Biochemistry; University of Colorado Boulder; Boulder CO USA
5. Department of Chemistry; University of California; Berkeley CA USA
6. Department of Physics; North Carolina A and T State University; Greensboro NC USA
7. NOAA-ISET Center; North Carolina A and T State University; Greensboro NC USA
8. Department of Chemistry; University of Helsinki; Helsinki Finland
9. Department of Chemistry; University of Washington; Seattle WA USA
10. Now at Department of Applied Physics; University of Eastern Finland; Kuopio Finland
11. National Center for Atmospheric Research; Boulder CO USA