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Assessment of a Remote Sensing Clean Screen Program

Project Description

A clean screen program identifies vehicles suspected of having low emissions and exempts them from regularly-scheduled I/M testing. Conversely, a high-emitter identification program requires more frequent testing of suspected high emitters. EPA has published guidance to states in implementing clean screen/high-emitter identification programs ( In this study we estimated the effectiveness of a hypothetical clean screen program based on remote sensing measurements, using data from Arizona. EPA has published the report (98K.pdf) on their website, and used the results in writing their guidance to states. Our analysis found that:

  1. A clean screen program would result in slightly larger losses of the emissions in excess of the IM240 cutpoints than a similar pilot clean screen program tested in Colorado.
  2. Less than one-third of the vehicles reporting for I/M testing were measured by the extensive remote sensing network utilized in the Phoenix area. This coverage rate drops to 20% if at least two remote sensing measurements are required per vehicle.
  3. Blanket model year exemption of the newest vehicles would be more effective than a remote sensing clean screen. A larger fraction of the fleet could be exempted, with a smaller amount of emissions in excess of the IM240 cutpoints lost (however MY92 and newer light duty trucks account for over 20% of excess NOx emissions from light duty trucks).

We also analyzed the effectiveness of using remote sensing clean screen versus model year exemptions for heavy duty (8,500 to 26,000 gvw) gasoline trucks. We found results similar to those for light duty vehicles; the results for heavy duty vehicles are summarized in a March 12, 1999 memo (98K.pdf) to EPA.

Analyzed the emission reduction potential lost by not repairing gross emitters in the Arizona fleet. Repairing all vehicles that never pass IM240 testing (including the 4% of failed vehicles that receive waivers) would nearly double the effectiveness of the Arizona I/M program; CO and HC emission reductions would be increased from 14% to 25%. Only about half of these additional emission reductions are attributable to vehicles identified as gross emitters by at least one remote sensing measurement. Reported results in a report (33K.pdf) to EPA.

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 Last Updated On: 8/19/04