Energy End-Use Forecasting
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Other Emissions

Project Description

Adjusting Short Test Emissions to Full Test Equivalents

One limitation of I/M data on in-use emissions is that all vehicles are not tested over the same controlled test procedure. For instance, most states using the IM240 allow the majority of clean vehicles to pass after only 30 seconds of the 240 second test; these short tests are referred to as "fast-pass" tests. In addition, some states, such as Arizona, allow dirty vehicles to fail after only 94 seconds of testing ("fast-fail" tests). Full IM240 emissions must be estimated before comparing emissions of vehicles tested over different durations of the IM240. We developed a simple method to convert fast-pass/fast-fail emissions results to full IM240 equivalents. We compared this method to methods developed by other researchers and EPA, to get a sense of the bias introduced by using each method. We found that each method tends to underestimate full IM240 emissions from fast-passed vehicles. The findings were summarized in a June 17, 1999 memo (293K.pdf) to EPA.

In-Use Emissions Deterioration

We analyzed average emissions by model year and odometer reading to examine trends in emissions deterioration as vehicle technology improves. Analysis of average emissions of MY93 and newer vehicles at high mileage (100,000 to 200,000 miles) indicates that newer technology is more durable. Tom presented results to the MSTRS In-Use Deterioration Workgroup (, and at the SAE Government/Industry Meeting (293K.pdf) in March 1997.

Modeling High Emitters

With Marc Ross of the University of Michigan, we identified four types of high emitters (running rich, running lean, misfire, bad catalyst), using second-by-second data from the UC Riverside modal emissions model project. We determined the distribution of each type of high emitter in the in-use fleet, using Phoenix IM240 data. The findings were presented at the 1998 SAE Fuels and Lubricants meeting (SAE Technical Papers). This analysis was incorporated into the high emitter module of the Comprehensive Modal Emissions Model, or CMEM, we developed in conjunction with researchers at UC Riverside and the University of Michigan ( We have also used state IM240 data to validate projected IM240 emissions from CMEM.

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TEMA Group Site The Enduse Forecasting Group, Lawrence Berkeley National Laboratory
 Last Updated On: 8/19/04