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Evaporative hydrocarbon emissions from gasoline-powered vehicles continue to be a major concern in areas where the national ambient air quality standard for ozone is violated. As a result, accurate estimates of real-world emissions from in-use motor vehicles are of vital importance in assessing the progress made in reducing emissions, as well as in determining the need for and required magnitude of additional emissions reductions. In this study, real-world evaporative emissions testing was performed on 50 late-model vehicles (30 passenger cars and 20 light-duty trucks), ranging in age from the 1992 to 1997 model year. Six of the 50 vehicles were equipped with enhanced evaporative emission control systems. Forty-nine of the 50 vehicles were procured from an Arizona State Inspection and Maintenance (I/M) Program test lane located in Mesa, Arizona, and one vehicle was procured from an employee of the test facility.

Two new, low cost methods used to identify inefficient or damaged catalytic converters were evaluated on in-use vehicles. The first technique was a non-intrusive propane injection catalyst test procedure developed by General Motors as part of their overall diagnostic strategy. The second technique utilized an Olympus fiber-optic borescope to visually assess the condition of catalytic converter substrates. Results from the two new techniques were compared against those from standard modal catalyst testing and IM240 tailpipe emission testing. The test results from seventy vehicles show the propane injection test to be generally effective at discriminating between converters with high and low conversion efficiencies. The fiber-optic borescope was less successful in identification of inefficient catalysts. This is because some catalyst failures are not readily identifiable while others have identifiable problems, but continue to perform at reasonable efficiencies.