Air quality activists have sued the U.S. Environmental Protection Agency, claiming officials illegally declared that the San Joaquin Valley has met the health standard for dust and soot.
Activists, who filed the lawsuit Tuesday in the 9th U.S. District Court of Appeals in San Francisco, say valley air monitors in January recorded dangerous levels of the pollution, called PM-10.
There have been several other violations in the past several years, they said.
"It's not just a violation of the law, it is complete and total disregard for our health," said Sierra Club member Kevin Hall of Fresno.
Federal officials said violations in the past few years have been legally excluded because of high winds. They said the valley's air has not exceeded the PM-10 standard since 2003.
"The valley continues to move toward cleaner air," said Deborah Jordan, air division director for EPA's Pacific Southwest region. "There is still more work needed to reduce smog and fine-particle pollution."
The nonprofit Earthjustice, a legal watchdog based in Oakland, filed the suit on behalf of the Sierra Club, the Latino Issues Forum and the Fresno-based Medical Advocates for Healthy Air.
The valley is known for some of the country's worst summer ozone and winter fine-particle pollution, called PM-2.5.
PM-10, a coarse particle prevalent in fall and winter, is about one-sixth the width of a human hair. It can trigger asthma attacks and heart problems, according to medical research.
Since 2002, a number of valley air rules have reduced such pollution. The rules included watering unpaved roads, reducing tilling on farm fields and cutting back on fireplace wood burning. Regional air officials have credited the rules with clearing much of the PM-10 problem.
But environmentalists and health advocates say monitoring data show that the PM-10 standard was surpassed on six days in 2006 and again on Jan. 4 this year. Earthjustice attorney Erin Tobin said the PM-10 problem has not gone away.
"EPA has just invented a new way to ignore it," Tobin said.