1. Department of Civil and Environmental Engineering Massachusetts Institute of Technology Cambridge MA USA
2. Now at Program in Atmospheric and Oceanic Sciences Princeton University Princeton NJ USA
3. Department of Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology Cambridge MA USA
4. Cooperative Institute for Research in Environmental Sciences (CIRES) University of Colorado Boulder CO USA
5. NOAA Chemical Sciences Laboratory (CSL) Boulder CO USA
6. Now at Ball Aerospace Boulder CO USA
7. Atmospheric Sciences Research Center University at Albany Albany NY USA