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Fueling cleaner air.

Two years ago, the big three U.S. automakers joined forces with 14 oil companies to investigate how changing the nation's mix of fuels and cars will likely affect urban air pollution. This Auto/Oil Air Quality improvement Research Program has just completed its first phase -- a series of tests that compared emissions from new (1989) and older autos (1983 to 1985 models) running on a wide range of experimental fuels. The more than 2,200 separate emission tests, involving 34 vehicles, quantified 150 components of exhaust and evaporative released. Researchers thon plugged the resulting 200 million data points into an air-pollution model for los Angeles to gauge how changing such factors as the temperature at which 90 percent of the fuel evaporates (T-90), or the percent of aromatics, olefins and sulfur in a fuel, could alter outdoor levels of ozone and other toxic chemicals.

"The biggest effect we saw was a 22 percent reduction in projected air releases of [volatile organic] hydrocarbons in the current vehicles when you reduced the T-90 from 360[degrees] to 280[degrees] F," observes Leo McCabe, a chemist and consultant with Mobil Research and Development Corp. in Paulsboro, N.J. That's important, he notes, because hydrocarbons are a major ingredient in the recipe for generating the ozone in urban smog. The lower T-90 fuel also proved the only experimental gasoline to lower all four "air toxics" monitored in this program -- benzene, formaldehyde, acetaldehyde and 1,3,-butadiene.

Oil companies produced the experimental, low T-90 fuel by removing the "heavy components" in today's gasoline, McCabe explains. The magnitude of this "heavy-end effect" proved both a suprised and a disappointment, McCabe adds, "because the reformulation [to reduce the T-90] is very expensive." However, he says, "if it needs to be done, we'll do it."

In general, the still-preliminary analyses indicate that reducing olefins, heavy components and sulfur is the most effective way of reducing ozone; altering a fuel's concentration of aromatics or oxygenates offered no clear ozone improvements. Reducing sulfur content proved the only reliable means of cutting all three major classes of vehicular emissions -- hydrocarbons, caron monoxide and nitrogen oxides.

Finally, these analyses indicate that phasing in the best reformulated fuel would reduce the automotive contribution to Los Angeles' ozone significantly--from 33 percent today, to only about 7 percent by the year 2010. However, the gradual disappearance of older, more-polluting vehicles is projected to reduce the share of LA's ozone from cars to 9 percent over the same period -- without any fuel changes. Is 2 percent less ozone worth the high cost of reformulating gasoline? Probably, McCabe says. In fact, "we feel that [our] goal of approaching zero emissions for the automobile is within reach."
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Author:Raloff, Janet
Publication:Science News
Date:Feb 29, 1992
Words:450
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