The water vapour self- and water–nitrogen continuum absorption in the 1000 and 2500 cm −1 atmospheric windows

Abstract

The pure water vapour and water–nitrogen continuum absorption in the 1000 and 2500 cm −1 atmospheric windows has been studied using a 2 m base-length White-type multi-pass cell coupled with a BOMEM DA3-002 Fourier transform infrared spectrometer. The measurements were carried out at the National Institute of Standards and Technology (NIST, Gaithersburg, MD) over the course of several years (2004, 2006–2007, 2009). New data on the H 2 O:N 2 continuum in the 1000 cm −1 window are presented and summarized along with the other experimental results and the continuum model. The experimental data reported on the water vapour continuum in these atmospheric windows basically agree with the most reliable laboratory data from the other sources. The MT_CKD (MlawerTobinCloughKneizysDavies) continuum model significantly departs from the experimental data in both windows. The deviation observed includes the continuum magnitude, spectral behaviour and temperature dependence. In the 2500 cm −1 region, the model does not allow for the nitrogen fundamental collision-induced absorption (CIA) band intensity enhancement caused by H 2 O:N 2 collisions and underestimates the actual absorption by over two orders of magnitude. The water vapour continuum interpretation as a typical CIA spectrum is reviewed and discussed.