History of Emissions Reduction: Normal Emitters in FTP-type Driving 2001-01-0229
Information is readily available on how a vehicle model's emissions system performs under certification conditions, but it is not widely known how it performs after years of use. This study predicts the odometer dependence of in-use car emissions, in grams per mile (gpm), over many model years. To do this, model years are analyzed starting in the mid 1980's until the mid 1990's. High emitters are eliminated from the study using a vehicle probability distribution technique. Emissions data was obtained from EPA's long-term Federal Test Procedure (FTP) survey, AAMA, CARB's Light Duty Vehicle Surveillance Program (LDVSP 14), and University of California Riverside CMEM database. The UCR data includes second-by-second engine-out and tailpipe-out emissions. Emissions system durability was found by comparing the emissions of vehicles of the same model year at different odometer readings. This data was fit to a linear function, enabling the emissions of vehicles to be determined at any odometer reading. The emissions of in-use vehicles were compared to the EPA certification standards at 50,000 and 100,000 miles, enabling evaluation of the artificial aging process of vehicles tested in the FTP. Tailpipe and engine-out emissions data are used to model the Catalyst Pass Fractions (CPFs) and cold start performance. In addition, certification FTP performance is compared to the corresponding EPA emissions standards. From this comparison, the amount of “headroom” (normalized difference between tested emissions and emissions standards) is computed. We put the gpm emissions of normal emitters, which we have been discussing, into context by briefly presenting estimates of emissions from the other sources: high emitters and driving patterns other than FTP-type. Thus we present an estimate of total “real-world” gpm emissions.