Temperature-dependent air broadening of water in the 1250-1750 cm−1 range

A Bruker IFS 120 HR Fourier-transform spectrometer has been used to investigate air broadening of water vapor at a spectral resolution of 3×10−3 cm−1 in the wavenumber range 1250-1750 cm−1. A new method for generating water vapor/air mixtures employing a 800 l stainless steel mixing vessel and a steady flow through the absorption cell has been developed. A total of 46 measurements have been recorded, 33 (26 water+air, 7 pure water) of which have been used in the final analysis. The measurements covered the temperature range 205-315 K, total air pressure range 50-1000 mb, water partial pressure range 0.001-5 mb, absorption path range 16-8500 cm and provided sufficient redundancy. Transmittance spectra corrected for various instrumental error sources were used in an automated single spectrum fit line parameter retrieval based on the Voigt profile. Average gas temperatures were fitted from retrieved water line strengths. From the retrieved Lorentzian line widths of each individual transition the air and self-broadening parameters and temperature exponents, γair, γself, nair, nself, or a subset thereof were fitted in an automated procedure. Various methods for validation of data product accuracy and data reduction model as well as comprehensive error analysis were applied. In total 593 γair, 459 nair and 469 γself values are reported, uncertainties for γair are given for reference temperatures 296 and 220 K. Only data are reported where the γair uncertainty is <2% or the γair,220 K uncertainty is <5%. The average uncertainties for γair, γair,220 K, nair, and γself are 0.7%, 2.2%, 0.07, and 3%, respectively. Comparisons with recent experimental work and HITRAN 2004 and HITRAN 2008 are presented.

► 46H2O/air measurements: T 205-315 K, Pair 50-1000 mb, abs. path 16-8500 cm. ► H2O: 593 γair, 459 nair, average uncertainties 1%, 0.07, range 1250-1750 cm−1. ► New method for defined water air mixtures in absorption cell. ► Validation of data product accuracy and data reduction model.