Measurement of air-broadening line shape parameters and temperature dependence parameters of H2O lines in the spectral ranges 1850-2280 cm-1 and 2390-4000 cm-1

Abstract

This paper describes the second part of an extensive study on absorption line parameters of water vapor in the spectral range 1850 - 4000 cm-1, dedicated to the use in ground based atmospheric measurements. Whereas the first part focusses on line positions, intensities and self-broadening line shape parameters, this work deals with air-broadening line shape parameters and temperature dependence. A Bruker IFS 125 HR Fourier transform spectrometer was used to measure air-broadened transmittance spectra of water vapor at 296 K and at low and high temperatures. 24 measurements were performed at 296 K and total pressures from 30 to 1000 mbar and 15 spectra were recorded at temperatures from 213 to 353 K at pressures of 90 or 100 mbar. A multispectrum fitting approach was used for line parameter retrieval applying a quadratic speed-dependent hard collision model extended to account for line mixing in the Rosenkranz approximation. Air-broadened widths, their speed-dependence, air-shift and in some cases collisional narrowing (Dicke-effect) and line mixing had to be fitted for modelling the 296 K measurements to the noise level. Measurements performed at low and high temperatures were used to retrieve temperature dependence parameters for air- and self-broadening, air- and self-shift and in a few cases for line mixing. For every parameter an extensive error estimation calculation was performed propagating several instrumental, measurement and parameter errors into individual parameter inaccuracies. The resulting parameters are presented, discussed and compared to the database HITRAN12. With this work the experimental line list is completed and the parameters are provided as supplement to this publication.