Publication Date


Document Type


Organizational Units

Chemistry and Biochemistry


Atmospheric chemistry, Emissions, Pollutants


A multi-year, on-road emission measurement program carried out in the cities of Chicago, IL, Denver, CO, Los Angeles, CA and Phoenix, AZ shows large, fuel specific tailpipe emissions reductions at all of the sites for carbon monoxide (CO), hydrocarbons (HC) and nitric oxide (NO). CO emissions decrease between 56% (Denver) and 71% (Chicago), HC emissions decrease between 27% (Phoenix) and 63% (Denver) and NO emissions have dropped between 48% (West LA) and 68% (Chicago). Three observed factors common to all of the sites are that the emission reductions are occurring in vehicles of all ages, that the influence of engine load on fuel specific emissions, especially for CO and NO, is reduced and that fleet averaged emission deterioration is near zero for model years newer than 2001 and older than 1990. These nationwide data sets imply that the majority of these on-road emissions reductions are the result of continued improvements in function and durability of vehicle emission control systems and that inspection and maintenance and fuel reformulation programs have only played a minor role.

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Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

Publication Statement

This is an Accepted Manuscript for

Bishop, G. A.; Stedman, D. H., A Decade of On-road Emissions Measurements. Environ. Sci. Technol. 2008, 42, (5), 1651-1656, DOI: 10.1021/es702413b.

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Gary A. Bishop, Donald H. Stedman


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English (eng)


28 pgs

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138 KB