The same catalytic converters credited with reducing harmful pollution from automobiles may produce large quantities of haze-causing ammonia, according to a recent report in the journal Environmental Science and Technology published by the American Chemical Society .
Ammonia plays a role in the formation of very small airborne particles.
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 the EPA's proposed regulation led to a legal case that the U.S. Supreme Court will hear this term. The researchers, led by Robert Harley, a professor at the University of California at Berkeley, found unexpectedly high levels of ammonia in the vehicles' exhaust. The most likely cause is the catalytic converter, he said. Engines that are not tuned properly also can contribute to ammonia formation, he added.