Global CFC-11 (CCl3F) and CFC-12 (CCl2F2) measurements with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS): Retrieval, climatologies and trends

Vertical profiles of CFC-11 (CCl3F) and CFC-12 (CCl2F2) have been measured with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) with global coverage under daytime and nighttime conditions. The profile retrieval is based on constrained nonlinear least squares fitting of measured limb spectral radiance to modeled spectra. CFC-11 is measured in its ν4-band at 850 cm-1, and CFC-12 is analyzed in its ν6-band at 922 cm-1. To stabilize the retrievals, a Tikhonov-type smoothing constraint is applied. Main retrieval error sources are measurement noise and elevation pointing uncertainties. The estimated CFC-11 retrieval errors including noise and parameter errors but excluding spectroscopic data uncertainties are below 10 pptv in the middle stratosphere, depending on altitude, the MIPAS measurement mode and the actual atmospheric situation. For CFC-12 the total retrieval errors are below 28 pptv at an altitude resolution varying from 3 to 5 km. Time series of altitude/latitude bins were fitted by a simple parametric approach including constant and linear terms, a quasi-biennial oscillation (QBO) proxy and sine and cosine terms of several periods. In the time series from 2002 to 2011, quasi-biennial and annual oscillations are clearly visible. A decrease of stratospheric CFC mixing ratios in response to the Montreal Protocol is observed for most altitudes and latitudes. However, the trends differ from the trends measured in the troposphere, they are even positive at some latitudes and altitudes, and can in some cases only be explained by decadal changes in atmospheric age of air spectra or vertical mixing patterns.ESA has provided MIPAS Level-1B data. Meteorological analysis data have been provided by ECMWF. Development of CFC-11 and CFC-12 data retrieval was partly funded by the German Federal Ministry of Education and Research (BMBF) under contract no. 50EE0901. We acknowledge support by Deutsche Forschungsgemeinschaft and Open Access Publishing Fund of Karlsruhe Institute of Technology. Partial support for NOAA/ESRL ground based measurements is from the Atmospheric Composition and Climate Program of NOAA's Climate Program Office.Peer Reviewe