title: A decade of on-road emissions measurements.
abstract: A multiyear, on-road emission measurement program carried out in the cities of Chicago, Illinois; Denver, Colorado; Los Angeles (LA), California; and Phoenix, Arizona shows large, fuel-specific tailpipe emissions reductions at all of the sites for carbon monoxide (CO), hydrocarbons (HC), and nitric oxide (NO). CO emissions decreased 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.
authors.affiliation: Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80208, USA. gbishop@du.edu
authors.forename: Gary A
authors.initials: GA
authors.lastname: Bishop
authors.forename: Donald H
authors.initials: DH
authors.lastname: Stedman
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D001335:Vehicle Emissions / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D001335:Vehicle Emissions