The North Coast has some of the cleanest air in the state while Lake County rates among the top 10 counties nationwide, according to the American Lung Association's 2012 "State of the Air" report, released Wednesday.
The ratings were similar to those in the association's last report in 2008.
Sonoma, Marin, Mendocino and Lake counties received A-ratings for overall clean air. But there remains room for improvement, said association spokeswoman Jenny Bard.
"While we're very pleased there aren't general (problems), there are still areas we know can be very unhealthy at the neighborhood level," she said. There are a limited number of air monitoring devices, so some neighborhoods could have high levels that aren't reflected in the data, she said.
"There can be very high levels of pollution just from one person burning" wood in a stove or fireplace, she said.
The study examined ozone and particulate matter. Ozone, or smog, is created when emissions react with sunlight and heat. Particulates come from combustion sources, including vehicles, power plants and burning of wood, Bard said.
Wood burning is the primary cause of particulate pollution in the Bay Area, she said.
Lake County was the only California county rated among the top 10 cleanest in the nation when it comes to annual air particulate measurements, Bard said. "It tied with Maui" for 8th place, she said.
The most particulate-free air in the country was measured in Santa Fe.
While Lake County rated well for particulate measurements on an annual basis, its short term, 24-hour particulate measurements failed to make the grade. That's because the study included the summer of 2008, when wildfires raged in area forests, Bard said.