Published in the Journal of the Air & Waste Management Association

Marc Ross, Rob Goodwin, and Rick Watkins
Physics Department, University of Michigan
Ann Arbor, MI 48109

Tom Wenzel
Lawrence Berkeley Laboratory
Environmental Energy and Technologies Group
Berkeley, CA 94720

Michael Q. Wang
Argonne National Laboratory
Argonne, Illinois 60439

It has long been recognized that vehicles emit more pollutants than allowed under the new car emission standards. Further tightening of the certification standards based on existing test procedures does not directly address the largest sources of emissions. This study attempts to quantify vehicle emissions by source, in order to prioritize future policy-making. Several new sets of data are used in conjunction with regulatory emission models to characterize the lifetime emissions from the average MY93 vehicle. Special attention is paid to two of the largest sources of real-world emissions: 1) high-power driving by cars with properly-functioning emissions controls, and 2) cars with malfunctioning emissions controls. Emissions are projected to MY2000 and 2010, based on estimates of the effectiveness of recently adopted and proposed regulatory policies. These new policies are projected to reduce total emissions substantially.

Despite large reductions in emissions from new cars, many metropolitan areas continue to suffer from poor air quality. Although current regulations have proven successful in reducing emissions from new cars in a standard test, most of the remaining emissions are from sources that may not be successfully addressed by existing policies. Continued emission reductions require new regulatory strategies that focus on the principal remaining sources of "real-world" emissions from cars. Better quantification of the major sources of vehicle emissions is necessary in order to carry out new regulatory strategies for continued emission reduction.

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