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High-Mileage Light-Duty Fleet Vehicle Emissions: Their Potentially Overlooked Importance
Gary A Bishop1, Donald H Stedman1, Daniel A Burgard2
1Department of Chemistry and Biochemistry, University of Denver , Denver, Colorado 80208, United States.
Environmental Science & Technology
|May 4, 2016
Summary
High-mileage vehicle fleets, like taxis and airport shuttles, emit disproportionately more pollutants than typically estimated. These specialized vehicles experience accelerated aging, significantly impacting mobile source emissions inventories.
Area of Science:
- Environmental Science
- Atmospheric Chemistry
- Transportation Engineering
Background:
- Activity-based computer models are standard for estimating mobile source emissions in the US.
- Current models assume uniform vehicle activity across emission classifications.
- This uniformity assumption may misrepresent the contribution of high-mileage fleets.
Purpose of the Study:
- To investigate the emission characteristics of high-mileage vehicle fleets.
- To determine if certain fleets contribute disproportionately to mobile source emissions.
- To assess the accuracy of current emission inventory models regarding fleet-specific aging.
Main Methods:
- Analysis of fuel-specific emission measurements from SeaTac Airport and Chicago.
- Comparison of emissions from hybrid taxis and airport shuttle vans with the general vehicle population.
- Evaluation of accelerated aging effects on emission control systems.
Main Results:
- Hybrid taxis showed increased emissions (CO, HC, NOx) by their fourth year.
- Airport shuttle vans exhibited accelerated catalyst aging (ammonia emissions) after 5-6 years.
- On-road taxis in Chicago had double the expected emission share relative to their fleet representation.
Conclusions:
- High-mileage fleets, despite being a small percentage of the total, represent a significant, often overlooked, source of mobile emissions.
- Accelerated aging in specialized fleets leads to higher pollutant outputs than standard models predict.
- Emission inventory models need refinement to account for the disproportionate impact of high-mileage vehicle fleets.
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