The CO2 tracer clock for the Tropical Tropopause Layer

1 Department of Earth and Planetary Sciences and the Division of Engineering and Applies Sciences, Harvard University, Cambridge, Massachusetts 02138, USA 2 NASA, Ames Research Center, Moffett Field, California 94035, USA 3 NOAA, Earth System Research Laboratory, Boulder, Colorado 80305, USA 4 University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, Florida 33149, USA 5 NOAA Aeronomy Laboratory, Boulder, Colorado 80303, USA 6 Oregon State University, College of Oceanic and Atmospheric Science, Corvallis, Oregon 97331, USA * now at: Department of Environmental Science Policy and Management, University of California, Berkeley, California 94720, USA