Dairy cows pollute less than oak trees

The ludicrous debate over how much dairy cows contribute to air pollution in California’s central valley is apparently just that — absurd.

Current regulatory estimates and environmental radicals say dairy cows emit smog forming so-called volatile organic gasses (VOCs) at rates higher than automobiles.

In reality, oak trees may be bigger contributors to smog than cows.

Frank Mitloehner, air quality Cooperative Extension specialist in the University of California, Davis animal science department, said current regulatory VOC dairy cow emission estimates are off tenfold and that trees and plants emit far more VOCs that cows.

Mitloehner deflated the bubble of environmentalists by measuring VOCs and other gasses in experiments conducted in “environmental chambers” — air tight cattle corrals fitted with air monitoring devices.

In fact, Mitloehner told the 35th annual Alfalfa and Forage Symposium in Visalia, Calif., recently that silage emits far more VOCs than cows. However, most silage in the valley is bagged or covered and that would greatly mitigate VOC emissions.

The total emissions for all measured organic carbonaceous gasses in the UC Davis studies were dominated by methane, a so-called greenhouse gas implicated in global warming, said the UC Davis scientist.

What dairy cows are emitting daily may eventually melt the polar ice cap, but it is not contributing nearly as much to the pollution in the central valley as many environmentalists and regulators believe.

“When cows were present in chambers, VOCs were less than 1 percent of total organic gas, which is a factor of 10 times smaller than historical estimates used by the air regulatory agencies,” said Mitloehner. This historical estimate was established almost seven decades ago.

California is the largest dairy state in the nation. Unfortunately, it is also home to two of the three worst air-sheds in the nation for ozone/smog pollution. One of those is the central valley.

Ship pollutants

However, Mitloehner said just because the smog is in the valley does not mean it originates there. He showed a satellite photo of container ships steaming in and out of the Bay Area, belching pollutants from their stacks that often find their way into the valley on prevailing winds. The aerial photo was almost black with container ship trails around Bay Area Harbors.

He also displayed satellite photos of polluting gases floating across the Pacific Ocean from China, one of the most polluted nations in the world, and other Asian countries adding to the valley’s smog problem.

The valley’s air pollution problems are more related to geography than internal pollution sources like cows, surmised the UC scientist. The valley is rimmed by mountains which prevent smog from escaping once it is blown in via prevailing winds from the West.

The debate over how much cows and dairies contribute to the smog has been all over the lot. That last study before the one now being conducted by Mitloehner was conducted in 1938 when it was determined that a dairy cow emitted 12.8 pounds of air pollutants per year. Back then it was identified as methane. There was no such designation as VOCs.

The San Joaquin Valley Air Quality District has determined that the VOCs from cows now total 19.3 pounds per year. Others have estimated at from 5.6 to 38.2 pounds of VOCs per year.

Studies prove errors

Mitloehner studies are proving everyone is wrong about VOCs and they were equally wrong about greenhouse gases, which the UC Davis scientist says are far larger than currently assumed by air quality agencies.

The ozone-forming potential of most of the VOCs measured in the experiments at Davis with state of the art analytical equipment of the most abundant VOCs measured is about only 20 percent of those typical combustions or plant-derived VOCs.

Mitloehner said decades of research at UC Riverside and UC Berkeley have identified plants as one of the most significant VOC sources. He cited oak trees as among the biggest VOC offenders.

“How do you regulate that? Chop down forests,” he commented.

e-mail: [email protected]

Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.