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Project at a Glance

Title: On-road measurement of light-duty gasoline and heavy-duty diesel vehicle emissions.

Principal Investigator / Author(s): Harley, Robert

Contractor: UC Berkeley

Contract Number: 05-309

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels


Emissions from light-duty (LD) gasoline and heavy-duty (HD) diesel vehicles were measured at the Caldecott tunnel in the San Francisco Bay area in summer 2006, with comparisons to results from previous years at the same site made to quantify emission trends over time. LD vehicle emissions of nitrogen oxides, volatile organic compounds, carbon monoxide, and particulate matter (PM) continue to decline over time due to fleet turnover effects and improved emission control technologies on new vehicles. Some effects of the switch from methyl-tert butyl ether (MTBE) to ethanol in California gasoline were observed. Substantial reductions in HD diesel truck emissions of PM were also observed between 1997 and 2006. The distributions of black carbon (soot) and ultrafine particle number emissions from individual diesel trucks were measured as part of this study, and sub-populations of high-emitting trucks were identified. NOx from HD trucks has been decreasing more slowly than for LD vehicles over the last decade, with the result that the relative importance of diesel engines as a source of NOx emissions in California has increased dramatically. Diesel engines are also an important source of direct emissions of aldehydes, which are malodorous, toxic, and reactive in the atmosphere. Exhaust emissions of ammonia from LD vehicles used to be negligible, then increased with the adoption of three-way catalytic converters, and appear to have declined since 1999 as carbon monoxide emissions and air/fuel ratio for LD vehicles have been brought under better control.


For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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