24 May 1999 00:00 [Source: ICB Americas]The two main oxygen additives used in reformulated gasoline in the US contribute little to reducing ozone pollution, according to a new analysis by a National Research Council committee.
In a study of the relative benefits of ethanol and methyl tertiary butyl ether (MTBE), the panel found that reformulated gasoline made with ethanol is less effective--but the overall impact of either oxygen additive on reducing ozone, a major component of smog, is very small.
Motor vehicle emissions of chemicals that form ozone have decreased in recent years, notes committee chairman William Chameides, regents professor of earth and atmospheric sciences at Georgia Tech in Atlanta.
"But that's largely because of better emissions control equipment and components of reformulated gasolines--other than oxygen additives--that improve air quality," says Mr. Chameides.
"Although additives do reduce some pollutants from motor vehicles emissions, the oxygenates appear to have little impact on lowering ozone levels. Moreover, it's not possible to attribute a significant portion of past reductions in smog to the use of these gasoline additives."
The oxygenated fuels industry counters that the report "is completely at odds with a host of real-world findings by state and federal environmental agencies over several years which show that reformulated gasoline with oxygenates is working effectively in helping to clean up our air."
The Oxygenated Fuels Association notes that as a result of the federal clean gasoline program, which began in 1995, air toxics have been reduced by 22 percent and emissions of volatile organic compounds have declined more than 27 percent.
Oxygenates dilute sulfur and other components in gasoline, making fuels work better, reducing engine deposits and protecting catalytic converters, the trade group explains.
The Clean Air Act amendments of 1990 require the use of reformulated gasoline with oxygen additives in areas of the US that have substantial ozone pollution. Such gasoline is sold in cities on the East Coast, in the Midwest, in Texas and in California--particularly during summer months, when low-level ozone is most prevalent.
Reformulated gasolines are designed to lower emissions of vehicle pollutants, including those that contribute to ozone formation. In addition to oxygen additives, the fuels have a number of other characteristics that reduce emissions.
But the oxygen additives in reformulated gasoline have raised environmental concerns. MTBE has leaked into drinking water in California, prompting the state to phase out its use of the additive.
Because questions persist over which types of reformulated gasolines are preferable, Environmental Protection Agency asked the research council to study methods for certifying gasoline blends with oxygen additives.
The committee found that, compared to MTBE blends, ethanol blends result in more pollutants evaporating from vehicle gas tanks. Ethanol blends also increase emissions' overall potential to form ozone.
However, available data indicate that the potential for either additive to reduce smog levels is small and will continue to decrease as other measures to reduce vehicle emissions take effect, the committee says. Tough air quality regulations and vehicle improvements during the last few decades have substantially reduced emissions that form near-ground ozone.
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