Magazine article Science News

Cars' Ammonia May Sabotage Tailpipe Gains

Magazine article Science News

Cars' Ammonia May Sabotage Tailpipe Gains

Article excerpt

Most people--even pollution experts--cite livestock waste as the leading source of urban, airborne ammonia. While that may have been true even a few years ago, a California study now indicates that cars have usurped this notorious distinction.

If confirmed nationally, the findings would show that vehicles make an unexpectedly large contribution to visibility-robbing haze. The good news, according to this study, is that only 10 percent of cars emit 66 percent of the ammonia. Identifying and correcting whatever distinguishes these heavy polluters could yield big gains, concludes the study's leader, Marc M. Baum of the Oak Crest Institute of Science in Baldwin Park, Calif.

Ammonia fosters a chemical transformation of acidic combustion gases, such as nitric acid, into dust-size airborne particles, such as ammonium nitrate. Less than a micrometer in diameter, such particles can be inhaled deeply and aggravate lung and heart disease (SN: 1/31/98, p. 68). Moreover, because these small particles pick up water, they can create a smoglike haze, explains Michael R. Hoffmann of the California Institute of Technology in Pasadena.

Ammonia's propensity to spawn such airborne particulates led governments to require factories to control ammonia emissions. Many use the alkaline chemical to neutralize acidic gases in smokestacks. No comparable regulations limit ammonia emissions from vehicles, however. In fact, Baum notes, since the advent of tailpipe catalytic converters, pollution scientists have written off cars as ammonia sources.

Until 2 years ago. That's when Glen R. Cass, then at Caltech, measured copious ammonia coming from vehicles passing through a Los Angeles tunnel. His data indicated that the metropolitan area's traffic spewed more than 25 tons of ammonia per day--about the same amount as area livestock did. …

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