Empirical age spectra for the midlatitude lower stratosphere from in situ...
Andrews, A. E., K. A. Boering, S. C. Wofsy, B. Daube, D. B. Jones, S. Alex, M. Loewenstein, J. Podolske, and S. Strahan (2001), Empirical age spectra for the midlatitude lower stratosphere from in situ observations of CO2: quantitative evidence for a subtropical "barrier" to horizontal transport, J. Geophys. Res., 106, 10257-10274.