Sonoma County got straight-A's on the American Lung Association's latest air quality report card, a rating it owes in large part to cool, breezy weather, officials said.
Vehicle exhaust emissions in Sonoma County, for example, are typically blown to the east and converted to hazardous ozone under a hot sun in Livermore, they said.
The Bay Area, including Sonoma County, benefits from a natural exporting of air pollutants to the Sacramento area and then south into the San Joaquin Valley, said Jenny Bard, advocacy manager for the American Lung Association of California.
More than one-fifth of northern San Joaquin County's air pollution originated in the Bay Area and Sacramento, she said.
Still, Sonoma County is a haven for clean air, one of only five California counties without a single day in three years (2010-2012) with ozone or particle pollution exceeding federal standards, according to State of the Air 2014, the Lung Association's report released this week.
The other four — Mendocino, Humboldt, Santa Cruz and Monterey — are also coastal counties, while Central Valley and Southern California counties had the highest levels of harmful pollution.
Lake County barely missed the list, with a single day of high ozone pollution from 2010 through 2012.
But Lake County ranked first in the nation for its year-round low level of particle pollution, with a "design value" of 3.5, far below the federal standard of 12, the report said.
Sonoma County, with a value of 8.0, was among the 30 California counties that earned a "pass" from the Lung Association, with annual exposure to particle pollution below the federal standard.
"It's great news and something we're proud of," said Brian Vaughn, a Sonoma County Department of Health Services division director, regarding the county's clean air standing. "One more good reason to live here."