VEHICLE EXHAUST-GAS MONITORING BY REMOTE FT-IR SPECTROSCOPY

An optically modified Unicam 0.25 cm(-1) resolution FT-IR spectrometer has been used for remote monitoring of absorption and emission spectr a of vehicle exhaust gases. In the active mode, a beam of modulated in frared radiation was emitted by the spectrometer and the absorption by the exhaust gas was measured along the beam path to a retroreflector. The return signal was monitored by a liquid-N-2 cooled mercury cadmiu m telluride (MCT) detector external to the instrument. The concentrati ons of CO and other gaseous molecular species in the exhaust were comp ared, with good agreement, with prepared laboratory samples and models based on the AFGL atmospheric transmission data-base HITRAN. In the p assive mode, the emission spectra of the warm exhaust gases have been recorded. The use of a liquid-N-2 background gave the spectrometer gre ater sensitivity to CO present in the exhaust gas. Laboratory studies at moderate (0.25 cm(-1)) spectral resolution have been conducted to d etermine the spectrometer sensitivity to trace concentrations of nitro gen and sulphur dioxide.