Washington D.C., August 20 -- Researchers presented evidence here today that cars may be the main source of haze-inducing ammonia, rather than livestock, as previously thought. The findings were presented at the 220th national meeting of the American Chemical Society, the world's largest scientific society.

In a study of 4,500 vehicles conducted on a southern California freeway ramp, researchers found unexpectedly high levels of ammonia in the exhaust of gasoline-powered cars. The levels were so high they estimate that cars are adding twice as much ammonia to the air of California's southern coastal basin as livestock do.

Ammonia plays a role in the formation of very small airborne particles, sometimes called "particulate matter." The U.S. Environmental Protection Agency recently targeted such particles for regulation under Clean Air Act standards on the grounds that they endanger human health. Opposition to EPA's proposed regulation led to a lawsuit that the U.S. Supreme Court will hear this term.

Until now, scientists believed that decomposition of livestock waste was the main source of atmospheric ammonia, according to Marc Baum, senior scientist at the Oak Crest Institute of Science and principal investigator for the study.

Some theorize that reformulated gasoline, introduced in the mid-1990s to lower sulfur and other emissions, has contributed to the increase in ammonia levels, Baum said. A recent study in the Aug. 15 issue of the journal Environmental Science & Technology, also published by ACS, reported that catalytic converters may play a role in rising ammonia emissions as well.

The evidence collected by Baum and his colleagues also suggests that a small share of the vehicles in the study produced most of the pollution. They found that 70 percent of the vehicles had detectable ammonia emissions, but just 10 percent generated 66 percent of the total emissions, according to Baum.

Using a measuring technique called remote sensing, the research team collected information on ammonia emissions on a car-by-car basis. This information, along with snapshots of the cars' license plates, enabled them to pinpoint the make and model of vehicles responsible for the elevated ammonia levels, Baum said.

Aside from cars and dairy farms, major sources of ammonia emissions include fertilizers and sewage treatment plants.

Although Baum's findings are based on cars in southern California, they "raise questions as to what ammonia emissions from on-road vehicles are nationwide," he said.

The paper on this research, FUEL 1, will be presented at 9:15 a.m. on Sunday, Aug. 20, in the Washington Convention Center, rooms 4-5.

Marc Baum, PhD., is a senior scientist at the Oak Crest Institute of Science, Baldwin Park, Calif.

A nonprofit organization with a membership of 161,000 chemists and chemical engineers, the American Chemical Society publishes scientific journals and databases, convenes major research conferences, and provides educational, science policy and career programs in chemistry. Its main offices are in Washington, D.C., and Columbus, Ohio.

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• Agriculture and Food
• Biology

• Petroleum
• Vehicles

• Environmental Issues
• Air Pollution

• Nitrogen oxide
• Automobile emissions control
• Catalytic converter
• Air pollution
• Fertilizer
• Methyl tert-butyl ether