Trace gases and aerosol observations by the FTIR-spectrometry

Ground-based solar absorption measurements using Fourier transform infrared (FTIR) spectrometry carry information about the atmospheric abundances of many constituents, including non-CO2 greenhouse gases. Such observations have been carried out since many years at six stations of the NDSC (Network for the Detection of Stratospheric Change) in western Europe, covering the polar to subtropical regions. At several stations, the observations span more than a decade. The FTIR solar absorption technique is the only remote sensing technique available nowadays with the potential of monitoring a number of greenhouse gases in the free troposphere.
This work focuses on the long-term FTIR observations at the above mentioned stations of primary and secondary greenhouse gases CH4, N2O, O3 and CO and C2H6, respectively. The existing spectral time series have been reanalyzed in order to derive distinct tropospheric and stratospheric abundances of the target gases, according to a common optimized retrieval strategy that is based on Rodgers Optimal Estimation theory. Trends of the tropospheric burdens of the target gases, and their uncertainties, have been evaluated where possible, using a bootstrap resampling method. In parallel, the Oslo CTM2 model has been used to simulate the time evolution of the target species and to estimate their evolution. The comparison between the model results and the observations will be discussed, as well as their agreement with expected values from in-situ observations and predictions, where available. The exploitation of the results for the validation of satellite observations will also be addressed.