In-Use Emissions from Heavy-Duty Diesel Vehicles

This paper reviews in-use emissions from over-the-road heavy-duty (greater than 8500 lb gross vehicle weight) diesel vehicles. Emissions of particulate matter (PM), oxides of nitrogen (NOx), carbon monoxide (CO), and hydrocarbon (HC) are considered. Emissions measurements have been made by chassis dynamometer, by remote sensing, and in tunnel studies. There is reasonable agreement between the different types of studies for emissions of NOx, but agreement for emissions of other pollutants is qualitative. Remote sensing studies indicate that emissions of NO are normally distributed, while emissions of CO and HC are skewed to a few high emitting vehicles. Chassis dynamometer results indicate that average emissions of PM, CO, and HC have been reduced during the past two decades, but average emissions of NOx have not changed. Thus, emissions regulations for PM have been somewhat effective, although the degree of PM reduction is less than expected based on changes in the standards. Emission regulations have app...