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Automobile time-resolved emissions of CO, CO2, HC, and NOx during engine and catalyst warm-up have been analyzed by fitting the emissions to the product of vehicle tractive power and a series of gaussian functions whose relative magnitudes were allowed to vary in time. From this analysis the emissions were discerned into four components : (1.) the emissions due to vehicle power demand, (2.) key-on emissions, (3.) a catalyst warm-up emissions function, and (4.) a fast idle emissions function. Both the emissions associated with the engine and the catalyst warm-up decline exponentially with time. Two additional characteristics (a.) emissions occurring during idling and (b.) emissions due to catalyst cooling during idle were observed, but not quantified.

Because of U.S. EPA regulatory actions and the National Academies National Research Council suggestions for improvements in the U.S. EPA emissions inventory methods, the U.S. EPA' Office of Transportation and Air Quality (OTAQ) has made a concerted effort to develop instrumentation that can measure criteria pollutant emissions during the operation of on-road and off-road vehicles. These instruments are now being used in applications ranging from snowmobiles to on-road passenger cars to trans-Pacific container ships. For the betterment of emissions inventory estimation these on-vehicle instruments have recently been employed to measure time resolved (1 hz) in-use gaseous emissions (CO₂, CO, THC, NO ) and particulate matter mass (with teflon membrane filter) emissions from 29 non-road construction vehicles (model years ranging from 1993 to 2007) over a three year period in various counties in Iowa, Missouri, and Kansas.

In June 2005, the United States Environmental Protection Agency (USEPA) signed a final rule implementing in-use testing requirements for heavy-duty diesel (HDD) engines. The program requires manufacturers to measure gaseous and particulate matter (PM) exhaust emissions from diesel engines using portable emission measurement systems (PEMS) installed on vehicles. In order to measure PM emissions, a cooperative contract between Sensors, Inc. and the USEPA was commenced to develop a Proportional Particulate Mass Device (PPMD). It is comprised of three key elements: a micro-proportional sampling system (MPS) incorporating an exhaust flow-meter (EFM) and an eight element quartz-crystal microbalance (QCM) to measure particulate mass. Evaluation of the exhaust flow meter (EFM) at third-party facilities have shown that the mass emission data and flow data produced with the EFM correlates extremely well with traditional (non-portable) constant volume sampling (CVS) certification systems.

The EPA is developing a new generation emissions inventory model, MOVES (Motor Vehicle Emissions Simulator). The first version of the model outputs fuel consumption based on available modal data. However, due to the limited heavy-duty vehicle data, MOVES pollutant (CO, HC, NOx) emission rates will need to be supplemented with rates determined with the Physical Emission Rate Estimator (PERE). PERE combines vehicle tractive power together with vehicle powertrain parameters specific to the class of vehicle; the vehicle weight, shape, engine type, and transmission. Analysis of in-use data for heavy-duty diesel tractor-trailer vehicles, city transit diesel buses, and dynamometer non-road diesel engines has enabled a determination of diesel engine friction and indicated efficiency and transmission shift schedules for these engines and vehicles. These model parameters and a comparison of the model results to measured fuel consumption and CO2 emissions are presented.