Published in the Proceedings of the
7TH CRC ON-ROAD VEHICLE EMISSIONS WORKSHOP
San Diego, California
April 9-11, 1997

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

Marc Ross
Physics Department, University of Michigan
Ann Arbor, MI 48109

With the adoption of high tech testing as part of state Inspection and Maintenance (I/M) programs, a wealth of data on in-use vehicle emissions is becoming available. Our analysis of California remote sensing data collected in 1991 found that five car models have CO malfunction rates of 15 to 30 percent, even though the cars were less than five years old at the time of the test. The five models were relatively inexpensive models of Asian manufacture, and almost all utilized carbureted fuel systems. We have recently analyzed I/M data from two states, 470,000 IM240 tests from Arizona and 1.4 million idle tests from Minnesota, to confirm our initial results. Our analysis indicates that there is little correlation between the remote sensing and idle test data. This is not surprising, since idle tests are not testing vehicle emissions under load. However, there is good agreement between the remote sensing and IM240 data, with most of the same models having high failure rates under each type of test. This agreement is somewhat surprising, given that the IM240 tests are on MY87-89 cars 4 years older than the comparable remote sensing tests. This result suggests that differences in emission control system durability continues for 10 years of vehicle life.

The IM240 data indicate that a different set of five MY91-93 models have CO malfunction rates of 10 to 20 percent. These five models, which were less than five years old at the time of the test, all use fuel-injection technology, and are manufactured domestically. The GM light duty truck engine family recently recalled by the California Air Resources Board shows up as one of the highest NOx emitters in the IM240 dataset. The IM240 data also allow us to analyze HC and NOx failure rates and mileage effects, all by vehicle model.

The ability of IM240 testing to identify vehicle models with emissions control problems within their warranty period can be helpful in improving various regulatory efforts to reduce in-use vehicle emissions. States can use the data as part of a "high emitter profile," in which cars with a higher likelihood of failing an I/M test are identified for more extensive I/M testing. EPA can use the data to compare the relative effectiveness of I/M programs adopted in different states. And EPA and CARB can use the data to target vehicle engine families for more extensive laboratory testing as part of their in-use compliance (recall) programs.

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