Oxygen in gasoline

May 31, 1999
A popular myth about gasoline chemistry has crashed against the hard wall of science.

A popular myth about gasoline chemistry has crashed against the hard wall of science.

The National Research Council, in a study for the U.S. Environmental Protection Agency, concludes that adding oxygen to reformulated gasoline harms more than helps air quality (OGJ, May 24, 1999, p. 39). Its findings puncture one of the most widely expressed yet scientifically questionable assumptions at work in the tortured politics of gasoline and the environment. The simple notion that oxygen makes gasoline "burn cleaner" has fostered a decade of confusion over reformulated gasoline. The notion is of course correct as far as it goes. But the extent of combustion, which oxygen certainly affects, isn't the whole story on vehicle emissions.

Ozone precursors

The reformulated-gasoline program, which EPA administers under the Clean Air Act Amendments of 1990, targets precursors to ozone smog: oxides of nitrogen and volatile organic compounds. Whether oxygen in reformulated fuels actually cuts emissions of those substances has long been doubtful. The program requires it nevertheless.

In combination with vehicle changes, reformulated gasoline has improved U.S. air quality overall. The NRC study notes that peak ozone pollution levels fell by about 10% in many metropolitan areas between 1986 and 1997. The question remains whether oxygen in reformulated gasoline had anything to do with the improvement. The study says it did not.

Oxygenates in general "appear to have little impact on lowering ozone levels," says NRC, an operating agency of the National Academy of Sciences, National Academy of Engineering, and Institute of Medicine. "Moreover, it is not possible to attribute a significant portion of past reductions in smog to the use of these gasoline additives."

This is not happy news for makers of gasoline oxygenates. The oxygenate favored by refiners, methyl tertiary butyl ether (MTBE), still reels from a phased ban announced Mar. 25 in California, where the substance has leaked into water supplies. And the oxygenate that stood to gain from MTBE's California setback, ethanol, takes an extra blow. Ethanol blends, the NRC study points out, generate more evaporative emissions than fuel containing MTBE and increase the overall potential of emissions to form ozone.

NRC's project isn't the first research effort to reach conclusions like these. Findings of a joint project of the automobile and oil industries, published in January 1997, also intensified longstanding doubt about the ozone-related advantages of adding oxygen to gasoline.

In fact, the oxygen mandate in reformulated fuel is just a political favor to ethanol makers and their farm-state political friends, who have been at pains for the past decade to overcome refiners' preference for MTBE over their product. One such exertion was EPA's politically motivated and judicially reversed rule that a certain share of the oxygenate added to reformulated gasoline come from renewable sources.

The NRC study itself stems from a similar effort on behalf of ethanol. EPA initiated the project at the urging of Sen. Richard Lugar (R-Ind.), a staunch ethanol supporter who hoped his favorite oxygenate would look preferable to MTBE in a scientific comparison of emission reactivity. NRC found no significant difference between the oxygenates by that standard and no good reason to make reactivity a factor in EPA's certification of reformulated fuel.

Program impediment

The requirement for oxygen in reformulated fuel is worse than unnecessary. To the extent it expands the fuel market for ethanol-which requires a tax subsidy-it aggravates ozone pollution and reduces government tax revenues. It has never had justification in science or economics. It is an impediment that exists only for political reasons to an otherwise successful fuel program.

The NRC study makes clearer than ever that the oxygen mandate in reformulated gasoline should cease.

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