On-Road Emission Performance of Late-Model TWC-Cars as Measured by Remote Sensing

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Abstract
During three days in September 1991, the Denver University remote sensor (FEAT) was used to measure the CO and HC emissions from 10,000 gasoline passenger cars on a freeway ramp in Goteborg, Sweden. The data have been used to study the emission performance of late-model three-way catalyst (TWC) cars as a function of age and as compared with earlier model years of noncatalyst cars. Regulations requiring the use of TWCs on all new gasoline passenger cars were adopted in Sweden beginning with model year 1989. Due to sales encouragement, a major fraction of model years 1987 and 1988 are also TWC-cars. The results show that the average volume %CO emissions were approximately 90 percent lower for the model years with exclusively TWC-cars compared to the pre-1987 (non-catalyst) model years. The figure deduced from the remote sensing readings for the corresponding reduction of average volume %HC emissions is uncertain due to liquid water occasionally present in the exhaust of some late-model cars, and interfering with the HC measurements. In the high emission region, no major differences in emission performance were observed between model years with exclusively TWC-cars. However, throughout the low emission region, CO emissions of model year 1989 and 1988 were approximately 50 and 100 percent higher when compared to model years 1990 to 1992. As for HC, probably due to poorer instrument sensitivity no differences in emission performance could be observed between the four latest model years, and only model year 1988 exhibited 15 to 20 percent higher emissions. Finally, the results of a limited data set indicate that for both CO and HC, emissions from TWCcars of model year 1987 were the highest. The observed differences in emission performance between model years in the low emission region are explained either by catalyst aging phenomena, and/or by a poorer initial performance of the first generations of TWC-systems introduced in Sweden.

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