1. Aeronomy Laboratory, National Oceanic and Atmospheric Administration (NOAA), Boulder, CO 80305, USA.
2. Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA.
3. School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA.
4. Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO 80307, USA.