Investigation of photometric errors in FTIR-spectra obtained in open-path monitoring

Open path monitoring of the atmosphere can be carried out using FTIR-spectr ometers, for which high sensitive, nitrogen cooled mercury-cadmium-tellurid e (MCT) detectors are routinely employed. Because of non-linearities in the MCT-detector response during the interferogram measurement and not correct ly compensated ambient blackbody emission, photometric inaccuracies arise f or mainly employed bistatic instruments with the unmodulated source radiati on being attenuated by atmospheric infrared absorbing species. Especially, the mid-infrared fingerprint-range is affected where many pollutants have t heir strongest spectral signatures. An important example is the determinati on of benzene in atmospheric air using the strong Q-branch absorption at 67 3.9 cm(-1), which is severely overlapped by the vl band of carbondioxide. ( C) 1999 Elsevier Science B.V. All rights reserved.