01551569

Component

While the phenomenon of excess vehicle emissions from cold-start conditions is well known, the magnitude and duration of this phenomenon is often unclear due to the complex chemical processes involved and uncertainty in the literature on this subject. This paper synthesizes key findings regarding the influence of ambient and engine temperatures on light-duty vehicle (LDV) emissions. Existing literature, as well as analytical tools like the U.S. Environmental Protection Agency’s Motor Vehicle Emission Simulator (MOVES), indicate that while total vehicle emissions have dropped significantly in recent years, those associated with cold starts can still constitute up to 80% for some pollutant species. Starting emissions are consistently found to make up a high proportion of total transportation-related methane (CH₄), nitrous oxide (N₂O), and volatile organic compounds (VOCs). After three to four minutes of vehicle operation, both the engine coolant and the catalytic converter have generally warmed, and emissions are significantly lower. This effect lasts roughly 45 minutes after the engine is shut off, though the cooling rate depends greatly on the emission species and ambient temperature. Electrically (pre-)heated catalysts, using the bigger batteries available on hybrid drivetrains and plug-in vehicles, may be the most cost-effective technology to bring down a big share of mobile source emissions. Trip chaining (to keep engines warm) and shifting to non-motorized modes for shorter trips, where the cold start can dominate emissions, are also valuable tactics.

This paper was sponsored by TRB committee ADC20 Transportation and Air Quality. Alternate title: The Problem of Cold Starts: Closer Look at Mobile Source Emission Levels

01550057

15-2371

English

15p

2015

Transportation Research Board 94th Annual Meeting

Digital/other

Figures; References

Cold starts (Driving); Exhaust gases; Light vehicles; Methane; Mobile sources; Nitrogen oxides; Organic compounds

Volatile organic compounds

Environment; Highways; Vehicles and Equipment; I15: Environment; I90: Vehicles

Transportation Research Board Annual Meeting 2015 Paper #15-2371

TRIS, TRB, ATRI

Dec 30 2014 12:50PM