ESTIMATING FULL IM240 EMISSIONS FROM PARTIAL TEST RESULTS: EVIDENCE FROM ARIZONA

The expense and inconvenience of enhanced-vehicle emissions testing using the full 240-second dynamometer test has led states to search for ways to shorten the test process. All states that currently use the IM240 allow some type of fast-pass, usually as early in the test as second 31, and Arizona has allowed vehicles to fast-fail after second 93. While shorter tests save states and drivers time and money, there is less data generated as results are no longer comparable across vehicles. This paper presents a methodology for estimating full 240-second results from partial test results for 3 pollutants: HC, CO, and NO sub(x). Using a random sample of vehicles in Arizona that received full 240-second tests, the authors use regression analysis to estimate the relationship between emissions at second 240 and emissions at earlier seconds in the test. The influence of other variables (age, model year) and the pollution level itself on this relationship are examined. The estimated coefficients are used in several applications. The frequent assertion that the results of the dynamometer test provide guidance for vehicle repair of failing vehicles is also examined. Using a probit analysis, findings indicate that the probability that a failing vehicle will pass the test on the first retest is greater the longer the test has progressed. The accuracy of estimates derived for forecasting fleet emissions from partial-test emissions results in Arizona are tested. The authors find that forecasted fleet average emissions to be very close to the actual fleet averages for light-duty vehicles, but not quite as good for trucks, particularly when NO sub(x) emissions are forecast.

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  • Corporate Authors:

    Air & Waste Management Association

    One Gateway Center, 3rd Floor, 420 Fort Duquesne Boulevard
    Pittsburgh, PA  United States  15222
  • Authors:
    • Ando, A W
    • Harrington, W
    • McConnell, V
  • Publication Date: 1999-10

Language

  • English

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Filing Info

  • Accession Number: 00798716
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Sep 12 2000 12:00AM