1. Department of Atmospheric Sciences; Texas A&M University; College Station Texas USA
2. Now at Institute for Meteorology and Climate Research-Atmospheric Aerosol Research, Karlsruhe Institute of Technology; Karlsruhe Germany
3. Chemical Sciences Division, Lawrence Berkeley National Laboratory; Berkeley California USA
4. Now at Department of Chemistry; University of the Pacific; Stockton California USA
5. W. R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory; Richland Washington USA
6. Science and Technology Branch, Environment Canada; Toronto Ontario Canada
7. Department of Atmospheric Sciences; University of Illinois; Urbana Illinois USA