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Cattle feed may contribute to ozone, smog

April 26, 2010

[Source: Associated Press and The New York Times Green Blog]

The smog in California’s San Joaquin Valley has puzzled scientists for years. Even though the region is largely rural and agricultural, its smog levels exceed those of densely populated cities like Los Angeles.

Some have speculated that animal waste or pesticides are the cause: both emit ozone, a primary ingredient in smog. But a recent study published in the Journal Environmental Science and Technology suggests that the primary culprit is actually cattle feed.

The study — funded by the U.S. Department of Agriculture, California Air Resources Board and the San Joaquin Valley Air Pollution Control District — initially was intended to measure the impact of animal manure, urine and flatulence on ozone levels. University of California, Davis researchers, however, found that the bigger ozone culprit appears to be millions of tons of fermenting cattle feed. This previously unrecognized source is likely the reason why ozone levels have not dropped even as the region has implemented control programs, scientists said.

Researchers found that animal feed is the largest emitter of ozone in the valley, at 25 tons per day, followed by motor vehicles at 14 tons.

Dairy operators long suspected that something other than the manure lagoons could be to blame and requested more studies. “We felt more likely it was coming from the fermentation process and likely the feed,” said Michael Marsh, executive director of Western United Dairymen.

“The take-home is that feed sources might be more important than all of the things we’ve been caring about in the past,” said Michael J. Kleeman, a professor in UC Davis’ department of civil and environmental engineering who was the study’s lead investigator.

When tests on animal waste failed to find as much ozone as expected, researchers turned their attention to the silage — giant mixes of corn, alfalfa, almond shells and corn stalks that’s piled to ferment under black plastic. The alcohol-drenched concoction is scooped with tractors and dumped into dairy cow feed troughs. Researchers found that the gases emitted during the fermentation react in the atmosphere to turn oxygen into ozone.  The main issue with feed seems to be the way it is stored. Cattle feed ferments when kept in an oxygen-poor environment, producing organic compounds, said Michael Kleeman, a professor of environmental engineering at the University of California at Davis and one of the study’s authors. When the feed is then placed in front of animals outside, those organic compounds are released to the atmosphere, contributing to ozone formation.

“The concentration of feed per square mile is the highest in the country,” Dr. Kleeman said. “The level of intensity in the San Joaquin is quite astounding.”

The San Joaquin Valley is the top dairy-producing region in the nation, with 1.5 million animals. And farms in the valley tend to be more crowded and cramped by comparison with the wide open fields of the Midwest, he added.

In their four-year study, the researchers captured feed emissions in a Teflon bag that they then exposed to ultraviolet light to reproduce the chemistry that occurs in the atmosphere on a sunny day. They measured the ozone concentrations that resulted and then drew on figures from the agriculture census to estimate the tons of ozone formed from animal feed each day.

The smog presents health concerns because it is known to be a factor in triggering asthma, bronchitis and emphysema as well as other heart and lung ailments.

The Environmental Protection Agency has said that if smog levels were more strictly controlled, 12,000 deaths from heart or lung diseases could be avoided annually. In January, the agency proposed stricter standards for smog-causing pollutants.

With air officials focusing for years on animal waste as the reason why smog is highest here despite having less vehicle traffic than large cities, many dairies invested in expensive methane digesters to deal with the problem.

Already the San Joaquin Valley Air Pollution Control District is working to amend emissions regulations to focus on new requirements for handling silage, said Executive Director Sayed Sadredin. In June, he plans ask the board to require that dairies bag their silage, a move that could cut ozone emissions by 90 percent.

While bagging silage adds expense, dairy operators say the cost is far less than a $2 million methane digester.

Journal Article Reference:

Howard et al. Reactive Organic Gas Emissions from Livestock Feed Contribute Significantly to Ozone Production in Central California. Environmental Science & Technology, 2010; 44 (7): 2309 DOI: 10.1021/es902864u

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One Comment leave one →
  1. May 1, 2010 11:44 pm

    wow fun info dude.

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