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Amonia Pollution Linked to Cars

Reformulated gasoline and catalytic converters introduced to reduce pollution may contribute to a different type of pollution - ammonia. Researchers have found evidence that cars may be the main source of haze-inducing ammonia, rather than livestock, as previously thought.

In a study of 4,500 vehicles conducted on a southern California freeway ramp, researchers found unexpectedly high levels of ammonia in the cars' exhaust emissions. The researchers 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.

Until now, scientists believed that decomposition of livestock waste was the main source of atmospheric ammonia. Some theorize that reformulated gasoline, introduced in the mid-1990s to lower sulfur and other emissions, has contributed to the increase in ammonia levels.

The evidence also suggests that a small share of the vehicles in the study produced most of the pollution. It was found that 70 percent of the vehicles had detectable ammonia emissions, but just 10 percent generated 66 percent of the total emissions.

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