Denver's air quality vs. the sticker price of a new car.
This is one example of the tough trade-offs Congress is wrangling over as it attempts to revise the Clean Air Act.
The political fight about high-altitude emission standards, combined with a score of similar congressional skirmishes, has gradually transformed deliberations on this key piece of environmental legislation into a bitter and drawn-out game of political chess.
The auto emissions issue has been complicated by scientific uncertainties that continue to comfound lawmakers' efforts to balance opposing interests - in this case, the interests of high-altitude Rocky Mountain states and those of Detroit.
At the center of the emissions debate are mandated tailpipe standards for two pollutants: carbon monoxide and nitrogen oxides. Because of the thinner air in places like the Mile High City, Salt Lake City, and Albuquerque, N.M., automobiles pour out substantially more of these pollutants than at sea level. So, in the 1977 amendments to the Clean Air Act, Congress slapped a schedule of increasingly stringent standards on the auto industry for these two pollutants and told Detroit it must meet them for ''all cars at all altitudes.''
Detroit and the Environmental Protection Agency (EPA) say these standards are too tough. According to General Motors, the emission levels - scheduled to take effect in 1984 - will result in a $480 cost penalty on 97 percent of all cars sold. This is a heavy price to pay to solve a problem caused by 3 percent of the fleet sold in those communities higher than 4,000 feet above sea level, GM says.
Also, the automakers and the EPA reckon that such stringent auto emissions standards are not necessary for areas like Denver to achieve national air quality standards.
Rep. John D. Dingell (D) of Michigan, House Energy and Commerce Committee chairman, has been the political vanguard for the attack on high emissions standards. Two weeks ago Mr. Dingell passed provisions in his committee to double the amount of carbon monoxide that cars would be allowed to produce at sea level, and triple it for cars operating at more than 4,000 feet. At the same time, however, he failed to persuade his fellow committee members to relax the nitrogen oxide levels. The result was a mixed victory for Detroit interests - according to GM, 88 percent of the cost to meet the standard comes from controlling nitrogen oxides.
Still, Mr. Dingell's action generated strong objections in Colorado. The state Department of Health, contrary to the automakers and EPA, estimates that Dingell's provisions would make it impossible for Denver to bring its air quality into compliance without such Draconian measures as mandatory van pooling and carless days.
Robin L. Dennis, a local air-pollution expert with the National Center for Atmospheric Research, explains that the conflicting predictions stem from differing assumptions about how well automobiles will perform at high altitudes and the growth in the number of miles traveled in this area.
Denver's air quality problems have been helped markedly since 1975 by significant reductions in emissions from new cars and from a recently started auto emissions inspection program. Current models emit about 90 percent less carbon monoxide than those of a few years ago. Under Dingell's proposals, today's autos would meet the revised standards.
Despite this improvement, continued growth of auto travel in the Denver area implies that the decrease in the carbon monoxide rate would slow, and then stop, says Dr. Dennis. Then, sometime around 1990, the levels would begin increasing again, he estimates. The tighter 1977 standards would give Denver a significant ''air quality cushion'' and push the possible reintroduction of carbon monoxide problems beyond the year 2000.
EPA and GM, on the other hand, project that such a relaxation only means a brief delay in the time when Denver's carbon monoxide levels fall below the proscribed level.
In the Senate, the legislative course of events has taken a different route. Under the stewardship of Colorado Sen. Gary Hart (D), a bipartisan bill favored by environmental groups and generally acceptable to Detroit passed the Senate Environment and Public Works Committee. This bill takes an entirely different approach from that taken in the House. It would allow automakers to add pollution control equipment only to cars sold in high-altitude areas.
In the past, similar ''two car'' proposals had foundered on car dealer opposition. Dealers in high-altitude areas have objected because such an approach would have reduced the number of models they could sell: Manufacturers will only offer the extra pollution control on a limited selection of cars. Senator Hart addressed this objection by allowing 15 percent of the cars to be sold without the added pollution control equipment.
The Senate committee also kept the stringent carbon monoxide levels set by the current law. The automakers would like to see this relaxed. Otherwise, they warn, diesels and some cars will have drivability problems at high altitudes.