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Developing a Better Understanding of Real-World Automobile Emissions

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Abstract: Emission inventories are needed by EPA for air dispersion modeling, regional strategy development, regulation setting, air toxics risk assessment, and trend tracking. Therefore, it is extremely important that inventories be accurate and be updated frequently. The development and update of emission inventories can be conducted from top/down using receptor models, or from bottom/up using emission factor models. Both of these approaches must address mobile source emissions which are a major source of air pollution. In the top/down approach, source profiles from mobile source emissions are needed; while in the bottom/up approach, mobile source emission factors are needed. In order to obtain realistic data, it is important that the source profile and emission factor data be obtained under realistic conditions. Vehicles must be tested under conditions that mirror their operation in the real world because operating conditions affect the character (source profile) and quantity (emission factor) of the emission. Operating conditions include such important variables as fuel (e.g., reformulated versus baseline gasoline), ambient temperature, driving mode (e.g., transient versus steady-state), and malfunction. The effect of malfunction on the quantity and character of emissions is not underestimated because most of the emissions come from the small minority of vehicles that are malfunctioning. Malfunctioning vehicles are found more often in the real world than in the laboratory.

Many of the studies conducted with the transportable dynamometer are sponsored in part by other agencies, such as the Department of Energy, Department of Transportation and California Air Resources Board. These studies investigated the mobile source particulate matter inventory using source receptor techniques. Air toxic emission factor data were provided for many of the vehicles tested in the studies. Other studies in Mexico and Texas have provided these two entities with emission factor data from vehicles operating in their areas. These data have been used for dispersion modeling and for the development of a regional strategy for addressing air quality issues. The dynamometer has also been shipped to locations to examine emissions from cars under unusual conditions. For example, the effect of extremely low-temperature operation with oxygenated fuels was examined in Fairbanks, Alaska.

Use of the transportable dynamometer is anticipated in future source apportionment studies. In particular, its use to obtain source profiles for gasoline vehicles operating within specific regions is envisioned. These data can be used in regional source receptor models to clarify and update existing emission inventories.

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Citation:Gabele, P. A. Developing a Better Understanding of Real-World Automobile Emissions. Presented at Science Forum 2003, Washington, DC, May 5-7, 2003.
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Contact: Liz Hope - (919) 541-2785 or hope.elizabeth@epa.gov
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Division: Human Exposure & Atmospheric Sciences Division
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Branch: Environmental Characterization & Apportionment Branch
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Product Type: Abstrct/Oral
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Presented: 05/06/2003
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Related Entries:
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Bullet Item Chemical Characterization & Speciation of Mobile Source Emissions: Human Exposure Implications & Implementation Perspectives
spacer Relationship Reason:   A Project of the Product
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Last Updated on Monday, October 22, 2007
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