1. Department of Chemistry; University of Toronto; Toronto Ontario Canada
2. Air Quality Division; Arizona Department of Environmental Quality; Phoenix AZ USA
3. Department of Atmospheric Science; Colorado State University; Fort Collins CO USA
4. Cooperative Institute for Research in Environmental Sciences; University of Colorado Boulder; Boulder CO USA
5. Chemical Sciences Division, Earth System Research Laboratory; NOAA; Boulder CO USA
6. Department of Chemistry; University of Colorado Boulder; Boulder CO USA