For regulatory policies to become more economical and effective in reducing pollution from automobiles, the computer emissions models used by environmental officials could take into consideration the differing maintenance of vehicles from the same model year, according to researchers at the University of California, Davis, University of Denver and the Desert Research Institute. Their research will be published in Friday's edition of the journal Science. While poor maintenance correlates with increasing vehicle age, differences in maintenance of vehicles from the same model year far outweigh the average effect of age, the researchers say. To date, U.S. Environmental Protection Agency computer models of emissions have treated all cars of a given model year as having the same odometer reading, same annual mileage and an equal likelihood of emission-control system problems, according to the researchers. Contrary to assumptions that "gross polluters" are just old vehicles, the researchers found that all model years of vehicles measured on the road, through remote sensing of exhaust carbon monoxide and hydrocarbon emissions, include some proportion of gross polluters. The highest emitting 20 percent of the newest cars were worse polluters than the lowest emitting 40 percent of vehicles from any model year, even those from model years before catalytic converters. And differences in emissions within a model year are greater than differences between the averages of the various model years. The study shows that "we need to focus on dirty cars as those we need to address to solve the problem. And it crosses all model-vehicle lines. The real surprise was that 10 to 20 percent of cars just over two years old were very dirty and running uncontrolled. Those cars are the real crux of the problem," says Lowell Ashbaugh, an associate research ecologist based at UC Davis' Crocker Nuclear Laboratory. To carry out their study, the researchers in 1991 placed on-road remote sensors at various urban locations in California, identified 66,053 vehicles and then collected records for them. The remote sensors take a half-second snapshot of the infrared absorption of carbon dioxide, carbon monoxide and hydrocarbon in the exhaust gases behind a moving automobile to determine the percent of these gases in the undiluted exhaust. A video camera records each license plate number so the make and model year can be determined through state motor vehicle records. In some instances, cars identified by the sensors as particularly strong polluters were pulled over and a voluntary California smog check (a tailpipe test and emission-control system inspection) was administered. The researchers found that 7 percent of the vehicles accounted for 50 percent of the on-road carbon monoxide emissions and 10 percent accounted for 50 percent of the hydrocarbon emissions -- all of these are considered "gross polluters." These gross polluters identified by the remote sensors were poorly maintained, or had been tampered with, the researchers say; the cars were not simply normally maintained vehicles temporarily emitting more pollutants because their engines were cold or they were accelerating hard. Ashbaugh says that while the findings of the newer cars as being high polluters have been noted before, little regulatory response has occurred. Some of the findings in the Science article were reported to the California Air Resources Board in the researchers' 1994 final report in their contract with the board, Ashbaugh says. The researchers note that ongoing regulatory programs to reduce automotive pollution, including transportation control measures such as mandated employee car pools, alternative and reformulated fuel programs and scrappage programs treat vehicles equally or operate on the assumption that older vehicles are more likely to be gross polluters. The researchers suggest that because of discrepancies in how people maintain their vehicles, a targeted repair program -- in which the worst 20 percent of all vehicles from each model year would be repaired to achieve the average emissions of the remaining 80 percent of the same model year -- would be the most cost-effective approach. Such a step would reduce hydrocarbon emissions by 50 percent and carbon monoxide emissions by 61 percent. Such a targeted repair program in California could be undertaken for an annual $11 fee per vehicle, with full costs of identification and repair raised during a four-year period. "Because the pullover study showed that about half the gross polluters had been illegally tampered with, the cost of the program would be cut in half if the owners of these vehicles were required to pay for their own repairs," according to the researchers. And even if repair costs were as high as $400 per vehicle, the targeted, subsidized repair program is still estimated to be the most cost-effective option to reduce ambient pollutants, the researchers say. Collaborating on the study with Ashbaugh were Stuart P. Beaton, Gary A. Bishop, Yi Zhang and Donald H. Stedman from the University of Denver, and Douglas R. Lawson, of the Desert Research Institute in Reno. The study was funded by the California Air Resources Board.