1. Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, Boulder, Colorado, United States
2. Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, United States
3. Aerodyne Research Inc., Billerica, Massachusetts, United States
4. Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
5. Chemistry Department, Boston College, Chestnut Hill, Massachusetts, United States
6. Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States