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Fourier Transform Infrared Spectroscopy (FT-IR) has been used to measure the exhaust emissions from vehicles during standard driving tests. Comparisons with conventional analyzers for modal tests have been made for the regulated species such as carbon monoxide (CO), nitrogen oxides (NOx) and total hydrocarbon (THC). The concentrations of methane, methanol and formaldehyde were also measured at one second time intervals during several driving tests. The average concentration values for these species were compared to the bag samples for several tests. Modal concentration curves were also calculated for MTBE, ETBE and several other species of interest. The results indicate FT-IR can be used for making modal measurements on the regulated species and non-regulated species in vehicle exhaust emissions. Several studies were performed to evaluate the long-term stability and sensitivity of FT-IR in actual test situations.

The IM240[1] inspection and maintenance test is being implemented in a number of cities throughout the country. This test, which requires the vehicle to be run on a chassis dynamometer, is designed to detect excessive exhaust emissions during different types of driving conditions. The present IM240 test procedure requires the use of four separate analyzers to provide modal information for CO, NOx, CO2 and total hydrocarbon from “in-use” vehicles. There are significant concerns about the calibration and complexity of this instrumentation for the level of use that is expected. A single FT-IR analyzer is capable of rapidly measuring the concentrations of many of the species found in tailpipe emissions. In this paper we will describe the results of a series of evaluation tests that we performed to compare the precision and accuracy of an FT-IR analyzer with the four analyzers presently used for the IM240 test.