Sonoma County stands alone in California with a perfect score atop the American Lung Association’s latest air quality report card for the state.

For the fourth straight year, the county earned a pair of A’s without a single day of ozone or particle pollution exceeding federal standards, according to State of the Air 2017, the association’s national report.

“You can’t have a better outcome than that,” said Will Barrett, a Sacramento- based senior planning analyst for the lung association.

Lake County came close, with a single day over the particle pollution standard, which measures soot, and the small inland county was fourth cleanest in the nation for year-round particle pollution.

Lake County had the second-lowest national rate last year, but massive wildfires in 2015 affected its score this year, Barrett said. Soot particles from wildfire smoke are a pernicious health hazard, triggering asthma attacks, heart attacks and strokes, the association says.

Mendocino County avoided high ozone counts, but had four days of high particle pollution in the new report, which covers three years from 2013 to 2015.

Sonoma County owes its consistently clean air to ocean winds that blow pollutants east, contributing to poor grades for Contra Costa and Solano counties, which had 16 and 18 days, respectively, exceeding the ozone and particle pollution standards combined.

Russian River area residents have complained about heavy smoke from wood-burning stoves, but Barrett said that neighborhood pollution may not register on the air quality monitors used to assess the whole county.

California cities continued to record some of the foulest air in the nation, with Visalia worst in year-round levels of particle pollution and Bakersfield with the largest number of high particle pollution days.

Los Angeles was No. 1 in the nation for in ozone pollution.

Statewide, 35 million people — more than 90 percent of the population — live in counties with unhealthy levels of either ozone or particle pollution, Barrett said.

Particle pollution comes largely from diesel engines and wood-burning fireplaces and stoves, he said.

Ozone comes primarily from tailpipe emissions in hot weather.

You can reach Staff Writer Guy Kovner at 707-521-5457 or On Twitter @guykovner.