Department of Civil and Environmental Engineering, Princeton University, New Jersey 08544, USA

Center for Mid-Infrared Technologies for Health and the Environment, Princeton University, New Jersey 08544, USA

now at: Advanced Study Program/Earth Observing Laboratory, National Center for Atmospheric Research, Boulder, Colorado 80307, USA

Department of Civil and Environmental Engineering, Princeton University, New Jersey 08544, USA

Center for Mid-Infrared Technologies for Health and the Environment, Princeton University, New Jersey 08544, USA

Mesoscale and Microscale Meteorology, National Center for Atmospheric Research, Boulder, Colorado 80301, USA

Department of Atmospheric and Oceanic Sciences, University of Colorado, Colorado, USA

Southwest Sciences, Inc., Santa Fe, New Mexico 87505, USA

Earth Observing Laboratory, National Center for Atmospheric Research, Broomfield, Colorado 80021, USA

Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado 80301, USA

Earth Observing Laboratory, National Center for Atmospheric Research, Broomfield, Colorado 80021, USA