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The use of catalytic converters in cars with gasoline engine results in a tremendous reduction of the emission of pollutant gases. The optimal operation of the exhaust treatment systems is being checked and maintained periodically, but there is always a significant percentage of cars with a malfunction of the catalytic converter causing a substantial percentage of the total emission. Roadside emission monitoring of individual cars in the running traffic could be used to indicate these gross polluters, arrange maintenance of their vehicles and thus reduce total emission. Present monitoring systems use non- dispersive IR spectroscopy. Other systems are based on mid- IR diode laser spectroscopy offering a higher signal to noise ratio, higher selectivity for detection of specific compounds and better optical quality for long open path measurements, but these systems depend on liquid nitrogen cooling. In this work a compact mid-IR (MIR) laser diode system for roadside measurements will be presented, that is cooled thermoelectrically using a Peltier element. Sensitivity and time resolution of the system have been determined and found to be suitable for detection of single gross polluters in the running traffic. The presented system demonstrates the feasibility of high sensitive, selective and fast field MIR laser diode spectroscopy together with ruggedness and low maintenance expense.
Kastner et al. (Thu,) studied this question.