Dirty Driving

Beginning last November, the Clean Air Act required drivers in 39 cities with carbon-monoxide problems to start using gasoline with such oxygen-enhancing additives as ethanol during the winter. Oxygenated fuels tend to reduce the amount of carbon monoxide cars emit.

But a government-sponsored audit of Colorado's four-year-old oxy-fuels program, published last December, deems oxygenated fuels an expensive and not very effective way to tackle carbon-monoxide emissions. Indeed, the authors of the audit argue that a remote-testing program that targets the highest-emitting cars might cut carbon-monoxide pollution for one-tenth the cost of oxy fuels.

Beginning January 1, 1988, Colorado required gasoline dealers to sell oxy fuels from the start of November until the end of February each year. In a study commissioned by the state auditor, Denver's PRC Environmental Management used remote-testing equipment developed by University of Denver chemistry professor Donald H. Stedman to collect data on the impact of this mandate. The infrared devices, which PRC testers set up on freeway on-ramps and at parking-garage entrances, can accurately measure the emissions from cars in motion. (See "Going Mobile," August/September 1990.)

From October 1991 until September 1992, PRC engineers measured emissions from more than 40,000 cars. They found oxy fuels do burn somewhat cleaner than regular gasoline. The average oxy-fueled car emitted 0.6 gram of carbon monoxide per mile, compared to 0.8 gram from the average gasoline-powered car.

But they also found that fewer than 10 percent of the cars they measured caused more than 50 percent of carbon-monoxide emissions. Most of these heavy smoggers weren't old cars—75 percent were 1983 model-year cars or newer—and oxy fuels alone would not clean them up. The highest-emitting 10 percent of oxy-fueled cars put out 3.5 percent carbon monoxide; by contrast, the cleanest 10 percent of gasoline-powered cars emitted less than 0.5 percent.

Overall, oxy fuels reduced carbon-monoxide emissions by 24,000 metric tons. The program cost government agencies, refineries, and consumers $25 million to $30 million. Thus oxy fuels cost Coloradans more than $1,000 for each ton of carbon monoxide eliminated. By contrast, using remote testing to identify and fix the dirtiest cars costs only $100 per ton.