API PUBL 4605-1994

$20.15

Investigation of MOBlLE5a Emission Factors: Evaluation of lM240-to-FTP Correlation and Base Emission Rate Equations

Published By	Publication Date	Number of Pages
API	1994	94

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Description

The U.S. Environmental Protection Agency's (EPA's) on-road motor vehicle emission factors model, MOBILE5a, is being used increasingly as a regulatory and public policy tool. It is used to determine compliance with motor vehicle related control programs such as enhanced inspection and maintenance (l/M) and highway conformity determinations; its outputs were also used to formulate EPA's Complex model for reformulated gasoline. Although MOBILE5a outputs are used for a broad array of purposes, the methods used to develop inputs to the model are largely undocumented. This report evaluates and documents the methods used by EPA to generate the exhaust base emission rate (BER) equations for MOBILE5a, which were developed from data collected with the IM240 test procedure at an operating I/M lane in Hammond, IN. EPA had to convert the IM240 data to a Federal Test Procedure (FIT) basis prior to developing the BER equations because the exhaust relations in MOBILE5a are based on emissions measured according to the FTP. This study critiques the adjustments used to correct the IM240 emissions test procedure for variations in fuel and temperature relative to those specified for the FTP, and it reviews the correlations between emissions based on the IM240 test procedure and emissions measured on the FTP. In addition, the methods used by EPA to develop emission control system deterioration rates for MOBILE5a were assessed and recommendations for alternative methods to estimate in-use Exhaust emission rates were made. The evaluation revealed that suspect statistical and analytical techniques were employed in the development and application of the IM240-to-FTP conversion procedure. Further, the methods used to generate exhaust base emission rate equations from the converted IM240 data resulted in a significant over prediction of emission rates at vehicle odometer readings above 75,000 miles.

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