1. S. A. Montzka, J. H. Butler, R. C. Myers, T. M. Thompson, J. W. Elkins, National Oceanic and Atmospheric Administration, Climate Monitoring and Diagnostics Laboratory, Boulder, CO 80303, USA.
2. T. H. Swanson, A. D. Clarke, L. T. Lock, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA.