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Emissions of particulate matter (PM) and oxides of nitrogen (NOx) from heavy-duty engines used in road vehicles and mobile equipment are of critical concern to air quality planners. Accurate measurement of these emissions is needed both for emission inventory purposes and for the development and validation of emission control measures. These emissions cannot adequately be predicted from laboratory tests on new engines. This paper reports the development of the Ride-Along Vehicle Emission Measurement (RAVEM) system. Based on the constant volume sampling (CVS) principle, the RAVEM system can accurately and repeatably measure mass emissions of NOx, CO2, and PM from an engine exhaust pipe while “riding along” on the vehicle or equipment under test. In most cases, this can be done without removing the vehicle from service. RAVEM test results have been shown to correlate very closely with those of conventional CVS emission laboratories.

Emissions from heavy-duty vehicles in real operation on the road often differ greatly from those that would be projected from laboratory testing. Reasons for this difference include variations between laboratory and real-world driving conditions, wear and deterioration that are not effectively modeled by laboratory tests, inadequate or inappropriate in-use maintenance, and the use of “cycle-beating” strategies and “defeat devices” by engine manufacturers. This paper analyzes data showing in-use emissions from heavy-duty diesel and natural gas vehicles tested using various driving cycles on chassis dynamometers. It is shown that average in-use emissions of particulate matter (PM) and oxides of nitrogen (NOx) from late model heavy-duty diesel engines are much higher than predicted by current emission models, and greatly exceed the emission standards to which these engines were certified.