The objective of the overall program was to provide light-duty vehicle emission data. These data are used by the EPA to calculate average emission factors from which emission source inventories and emergency episode pollution abatement procedures are developed. Other objectives included the development of short cycle emission test data and on the costs and effectiveness of high altitude vehicle maintenance specific to the Denver site. The short cycle evaluation task data are used by the EPA to establish correlations between selected short cycle emission tests and the more sophisticated emission testing procedures. Tests were performed on a sample of six-hundred and seventy-nine (679) 1972 through 1976 model-year vehicles operating in the Denver metropolitan area. Ten 1975 model light-duty trucks were used in connection with emission factors development, short cycle evaluation and a task designed to develop data on emission related costs and effectiveness of high altitude vehicle maintenance specific to the Denver area.

Project Officer: John C. Shelton. Automotive Testing Laboratories. Contract Number: EPA Contract No. 68-03-2183 "October 1976." "EPA-460/3-76-013."

Tests were performed on a sample of six-hundred and seventy-nine (679) 1972 through 1976 model-year vehicles operating in the Denver metropolitan area. Ten 1975 model light-duty trucks were included in the sample. This vehicle sampling was used in connection with emission factors development, short cycle evaluation and a task designed to develop data on emission related costs and effectiveness of high altitude vehicle maintenance specific to the Denver area. The program was conducted in two phases. In the first phase, two hundred and nine (209) vehicles, which are similar to vehicles tested in other sites under this contract, were tested in the as-received condition. These tests were performed in this and the other sites in connection with emission factors development and short cycle evaluation. The ten trucks were included in this sampling. With the exception of the ten trucks and five of the passenger cars, these vehicles were tested again after maintenance in connection with the Denver Inspection/Maintenance Evaluation Task. This maintenance included the restoration of emission control hardware which had been disabled and an emissions-oriented tune-up. In the second phase, an additional four hundred and seventy (470) vehicles were tested relative to the Denver Task. These vehicles were initially subjected to an idle mode emissions screening test, the standards for which were selected from Phase I data to fail thirty-five percent of the highest emitting vehicles by this test. Those vehicles which failed the inspection test were subsequently tested by the more sophisticated laboratory procedures, maintained and retested by these procedures. Maintenance of these vehicles was performed using the same procedures applied in Phase I. Test procedures specific to emission factors development included the Federal Test Procedure, the Surveillance Driving Sequence and Steady State Procedures. Two additional variable driving schedule mass emission tests were also conducted. One schedule has an average speed lower than the Federal Test Procedure; the other a higher average speed. Procedures specific to the short cycle evaluation included the Clayton Key Mode, the Federal Short Cycle and the Federal Three Mode Tests. The Denver Inspection/Maintenance Evaluation Task included several of the above listed procedures and a hot start version of the Federal Test Procedure (Hot Short FTP), the Two Speed Idle Test, the Inspection Test and a test to evaluate catalytic converter efficiency, in addition. Fuel economy data were also obtained for vehicle operation connected with the Federal Test Procedure, the Hot Start FTP, the High and Low Speed driving cycle mass emission tests, the Highway Fuel economy Test procedure and other of the mass emission tests.