Smog wars: changing rules, weighing fuels.

Smog wars: Changing rules, weighing fuels

EPA proposed new rules last week to limit the leading source of hydrocarbon pollution from motor vehicles -- emissions of evaporated gasoline trapped in the tank and fuel lines. Agency officials say the rules, which they hope to implement within three years, should reduce U.S. air emissions of volatile organic compounds by about 5 percent. Volatile organics represent a major cause of smog ozone.

U.S. vehicles already contain charcoal canisters to trap gas vapors from parked cars. However, recent fuel-volatility increases allow cars parked for a day or longer to develop such a massive buildup of vapor -- especially on the hottest summer days, when smog tends to be worst -- that it can overwhelm today's collection systems. The new rules would require larger canisters, as well as vapor-purging improvements in fuel-distribution systems to ensure that even under most summer time conditions, gas flows only to the engine or charcoal canisters once the car is restarted.

Researchers are weighing methanol, an alternative to gasoline, as another major recruit into the war on urban ozone. A new analysis of the alcohol fuel's potential to combat smog throughout the Los Angeles basin -- the nation's most ozone-troubled region -- indicates that running all new vehicles there on methanol starting this year could reduce peak ozone levels by about 13 percent by the year 2000 and lower by 22 percent human exposures to ozone levels exceeding the federal standard, according to a report in the Jan. 12 SCIENCE. And if cities begin controlling ozone-precursor chemicals emitted by industrial boilers, "our studies show going to methanol vehicles can have an even bigger impact"--easily a 20 percent ozone reduction by 2000, says study leader Ted Russell at Carnegie Mellon University in Pittsburgh.

Unlike earlier computer studies of methanolhs smog-limiting potential, which confined their analyses to small air parcels, Russell's model covers an entire metropolitan area, "from downtown to downwind." It also includes previously omitted variables accounting for most of the chemistry and physics influencing reactions between air pollutants, he says. The new analysis shows that even though methanol-run vehicles can emit five times as much formaldehyde as gasoline-fueled cars, a shift to methanol should not worsen urban formaldehyde concentrations and might even improve them. Other emissions from gasoline-fueled vehicles react with pollutants in the air to create more formaldehyde than methanol vehicles spew directly, Russell explains.