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December 1997 /
January 1998

Drive-by sampling: UCAR and Boulder team up for emissions checks


UCAR, the city of Boulder, and the University of Denver (DU) are collaborating on an environmental awareness program focused on the automobile's role in wintertime air pollution. Late in January, drive-by emissions monitoring will be performed near the Mesa and Foothills Labs (one morning at each site). The most egregious emitters will be offered a $25 voucher toward a tune-up or other emissions-related auto work.

You may already have encountered the monitoring device that's coming to UCAR. It was developed by DU chemistry professor Don Stedman and deployed for over a year just off Interstate 25. Motorists exiting south on Speer passed a beam of infrared light at hubcap level that monitored tailpipe emissions for a half-second. Moments later, a large sign informed each driver about her or his vehicle's performance in qualitative terms ("good," "fair," or "poor"). The technique gives readings for carbon monoxide, hydrocarbons, and nitric oxide as a ratio of their emission levels to that of carbon dioxide; this allows for accurate sampling despite varying environmental conditions.

Stedman's device is based on many of the same principles as the dynamometer used by Envirotest, the state's official emissions tester. However, Stedman samples emissions on the fly rather than capturing them in a box for analysis, as do the official tests. Stedman's invention can sample hundreds of cars in an hour, a much faster pace than the official tests allow.

Why do this check-up when we're already required to get comprehensive tests on our vehicles every two years? The city wants to help fix those few autos that squeak by Envirotest yet still produce big-time emissions on the road. The less efficiently a car runs, the more its performance varies, which can enable borderline cars to sneak through on a repeat emissions test. According to Stedman, the lowest 10% of passing-grade vehicles produce more emissions than the other 90% put together. Older cars, as a rule, produce more emissions, but less than half of pre-1974 cars are gross polluters, and there are environmental lemons among some newer models as well.

How will it work?

This schematic diagram depicts the on-road emissions testing system to be deployed at UCAR in January . Infrared light ("IR Source") shines through a vehicle's exhaust stream to a detector across the road. The detector measures measure the infrared absorption and thus determines the pollutant concentrations. A video camera takes a picture of the rear of each passing vehicle, from which the license plate can be identified. The system has been tested since 1987 and at speeds between 3 and 245 kilometers (2 and 152 miles) per hour. (Illustration courtesy Don Stedman/University of Denver.)

Assuming that about 500 cars pass a given site on a given morning, Stedman estimates that "the worst 25 cars are going to be emitting as much carbon monoxide as the other 475 cars put together." Stedman's system can measure a number of emission types, but CO is the main gas of concern, as it's the only one for which Boulder still fails federal air-quality guidelines on some days. "It's a very good indicator of how efficiently a car is burning fuel," notes Stedman. While most cars show CO emission values of less than 1% and many will be below 0.1%, the worst emitters will be in the neighborhood of 4%, ten times above the average.

The city will pay for the demonstration monitoring program, including the DU team's time, and UCAR and the city will jointly subsidize up to 40 of the $25 vouchers. If the sampling at UCAR goes well, the city plans to work with other employers to offer similar programs. "Cars are the largest source of our air-pollution problem," notes city environmental specialist Julie Herman, "and it's just going to get worse with time." At current growth rates, there will be 30% more cars in Boulder County in 13 years. Between 1994 and 2020, vehicle miles traveled in the county are projected to nearly double, from 2.5 to 4 million per day. •BH

Don Stedman's Web page links to a set of lecture notes on the science and politics of automotive emissions and on his testing system. Stedman and colleagues will give general-interest seminars at ML and FL before the January sampling; watch This Week at UCAR for details.

City residents can take advantage of a variety of rebates, including $75 for woodstove upgrades, $40 for furnace tuneups, and 25% of the cost (up to $100) for replacing a polluting lawnmower with a cleaner one. For questions or more information on Boulder air quality concerns, contact the city at 441-3878 or check the county's Web site.

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Edited by Bob Henson, bhenson@ucar.edu

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