Articles | Volume 7, issue 9
Atmos. Meas. Tech., 7, 2907–2918, 2014
Atmos. Meas. Tech., 7, 2907–2918, 2014

Research article 10 Sep 2014

Research article | 10 Sep 2014

Derivation of tropospheric methane from TCCON CH4 and HF total column observations

K. M. Saad1, D. Wunch1, G. C. Toon1,2, P. Bernath3, C. Boone4, B. Connor5, N. M. Deutscher6,7, D. W. T. Griffith6, R. Kivi8, J. Notholt7, C. Roehl1, M. Schneider9, V. Sherlock10, and P. O. Wennberg1 K. M. Saad et al.
  • 1California Institute of Technology, Pasadena, CA, USA
  • 2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
  • 3Old Dominion University, Norfolk, VA, USA
  • 4University of Waterloo, Waterloo, Ontario, Canada
  • 5BC Consulting, Ltd., Alexandra, New Zealand
  • 6University of Wollongong, Wollongong, Australia
  • 7University of Bremen, Bremen, Germany
  • 8Finnish Meteorological Institute, Sodankylä, Finland
  • 9Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 10National Institute of Water and Atmospheric Research, Wellington, New Zealand

Abstract. The Total Carbon Column Observing Network (TCCON) is a global ground-based network of Fourier transform spectrometers that produce precise measurements of column-averaged dry-air mole fractions of atmospheric methane (CH4). Temporal variability in the total column of CH4 due to stratospheric dynamics obscures fluctuations and trends driven by tropospheric transport and local surface fluxes that are critical for understanding CH4 sources and sinks. We reduce the contribution of stratospheric variability from the total column average by subtracting an estimate of the stratospheric CH4 derived from simultaneous measurements of hydrogen fluoride (HF). HF provides a proxy for stratospheric CH4 because it is strongly correlated to CH4 in the stratosphere, has an accurately known tropospheric abundance (of zero), and is measured at most TCCON stations. The stratospheric partial column of CH4 is calculated as a function of the zonal and annual trends in the relationship between CH4 and HF in the stratosphere, which we determine from ACE-FTS satellite data. We also explicitly take into account the CH4 column averaging kernel to estimate the contribution of stratospheric CH4 to the total column. The resulting tropospheric CH4 columns are consistent with in situ aircraft measurements and augment existing observations in the troposphere.