Cow pass Cars as San Joaquin Valley worst polluters

Got smog?

California's San Joaquin Valley for some time has had the dirtiest air in the country. Monday, officials said gases from ruminating dairy cows, not exhaust from cars, are the region's biggest single source of a chief smog-forming pollutant.

ADVERTISEMENT

Every year, the average dairy cow produces 19.3 pounds of gases, called volatile organic compounds, the San Joaquin Valley Air Pollution Control District said. Those gases react with other pollutants to form ground-level ozone, or smog.

With 2.5 million dairy cows — roughly one of every five in the country — emissions of almost 20 pounds per cow mean that cattle in the San Joaquin Valley produce more organic compounds than are generated by either cars or trucks or pesticides, the air district said. The finding will serve as the basis for strict air-quality regulations on the region's booming dairy industry.

The San Joaquin Valley, Houston and Los Angeles have the three worst air-pollution problems in America. Their relative rank varies from year to year depending in part on weather conditions. Over the last six years, however, the San Joaquin Valley has violated the federal limit on ozone smog over an eight-hour period more than any other region. That "eight-hour standard" is the U.S. Environmental Protection Agency's main barometer for the severity of smog.

The dairy industry will be forced to invest millions of dollars in expensive pollution-control technology in feedlots and waste lagoons, and may even have to consider altering animals' diets to meet the region's planned air-quality regulations. Not surprisingly, industry officials challenged the estimate as scientifically unsound.

"Science is supposed to guide this regulation, not fairy dust," said Michael Marsh, chief executive officer of Western United Dairymen, a lobbying group that said it was considering a lawsuit to block regulations based on the new finding. "It's impossible to capture emissions that scientists can't even detect."

Air-quality regulators defended their estimate as a conservative one based on the best available research. But it was criticized by some scientists — including one whose work was used by the district to arrive at the figure.

"If you closed all the dairies in California tomorrow, you would not see much of an impact on ozone formation," said the scientist, Frank Mitloehner of UC Davis, who was hired by air-quality officials to study cow emissions and now contends his findings were misconstrued.

"We really don't have the science to back this number up," he said.