Long-term validation of tropospheric column-averaged CH4 mole fractions obtained by mid-infrared ground-based FTIR spectrometry [Discussion paper]

At the Izaña Atmospheric Research Center, highresolution mid-infrared solar absorption spectra have been recorded for more than 12 yr using Fourier Transform InfraRed (FTIR) spectrometers. We use the spectral fitting algorithm PROFFIT to retrieve long-term time series of methane (CH4) from the measured spectra.M. Schneider is supported by the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007-2013)/ERC Grant agreement number 256961. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) within the NORS project (grant agreement no. 284421)