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A Fuel-Based Approach to Estimating Motor Vehicle Cold-Start Emissions
Brett C Singer1, Thomas W Kirchstetter1, Robert A Harley1
1a Department of Civil and Environmental Engineering , University of California , Berkeley , California , USA.
Journal of the Air & Waste Management Association (1995)
|January 14, 2017
Summary
Vehicle emissions are much higher during cold starts due to ineffective controls. This study found that cold-start emissions may be overestimated in current inventory models, suggesting a need for revised calculations.
Area of Science:
- Environmental Science
- Atmospheric Chemistry
- Automotive Engineering
Background:
- Motor vehicle emission controls are temporarily ineffective at startup, leading to significantly higher emission rates compared to stabilized operation.
- Official emission inventories suggest cold-start emissions constitute a substantial portion of total hydrocarbon, carbon monoxide (CO), and nitrogen oxide (NOx) from vehicles in California.
Purpose of the Study:
- To verify real-world cold-start emission estimates under actual driving conditions.
- To compare measured cold-start emission factors with those used in California's Motor Vehicle Emission Inventory Model (MVEI 7G).
Main Methods:
- Vehicle emissions were measured in an underground parking garage in Oakland, CA, during March 1997.
- Hot stabilized emissions were recorded as vehicles arrived, and cold-start emissions were measured as they exited.
- Incremental emissions from starting were calculated by difference, with composite samples from approximately 135 vehicles.
Main Results:
- Measured stabilized emissions: 19 g NMHC, 223 g CO, and 8.6 g NOx per gallon of gasoline.
- Measured cold-start emissions (approx. 60 seconds): 69 g NMHC, 660 g CO, and 27.8 g NOx per gallon.
- Scaled incremental emission factors per vehicle start: 2.1 g NMHC, 16 g CO, and 2.1 g NOx.
- These factors are 45% lower for NMHC, 65% for CO, and 12% for NOx than MVEI 7G estimates.
Conclusions:
- The contribution of cold-start emissions to overall vehicle pollution may be overstated in current emission inventories.
- While the composition of volatile organic compound (VOC) emissions is similar, unburned fuel and acetylene are higher during cold starts.
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