High resolution Fourier Transform spectroscopy at DLR for improving the spectral database of atmospheric species

Abstract

The DLR spectroscopy group has carried out high resolution Fourier-Transform spectroscopy of atmospheric species since 1990. The work started in the far-infrared, was extended to the nearinfrared and is recently expanded up to the UV region. The measurement of spectroscopic data with small and defined error margins was always the main target. The Fourier-Transform instrument including measurement conditions were optimized and sample cells and gas handling equipment built. Numerous software tools for retrieval and quality assessment were developed. Methods and hardware have been made for generating defined water/air and ozone/air mixtures including transport/flow into the sample cell. Species covered over the years are OH, HO2, H2O, CO, NO, NO2, O3, ClO, ClOOCl, BrO, CO2, ClONO2, N2O5 and very recently BrONO2. In many cases the resulting absorption cross sections and line parameters are included in the HITRAN database. The most recent development in hardware will be presented including a completely refurbished coolable multireflection cell (base length 80 cm, absorption path >150 m) and a four window coolable short cell, both capable of measurements from FIR to UV with excellent temperature homogeneity. A new fitting software was developed capable of performing microwindow-based interactive multi spectra fits making use of several line shape models, including, but not limited to, the pCqSDHC model [1] extended for Rosenkranz line mixing. The first result obtained is the analysis of pressure broadened ambient temperature N2O ν3 rovibrational band requiring speed dependence and line mixing. [1] N. H. Ngo, D. Lisak, H. Tran and J.-M. Hartmann, "An isolated line-shape model to go beyond the Voigt profile in spectroscopic databases and radiative transfer codes," Journal of Quantitative Spectroscopy and Radiative Transfer, no. 129, pp. 89-100, 2013.