Marin County received mixed grades in a nationwide air-quality report released last week by the American Lung Association, which for 18 years has graded cities and counties for ozone and particulate pollution. The latter has long been considered troublesome in the San Geronimo Valley, where the topography traps wood smoke. The association, which offers grades based on Environmental Protection Agency air monitors—Marin’s is located in San Rafael—gave the county an A for ozone levels, a greenhouse gas largely the result of tailpipe emissions. There were no days when the county exceeded ozone standards—a consequence, at least in part, of coastal winds that tend to blow ozone inland, said Jenny Barth, a spokeswoman for the group. But for particulate pollution spikes, Marin received a C. Over the three-year grading period from 2013 to 2015, the most recent data available, there were five days when Marin exceeded particulate pollution levels considered to be harmful. “A lot of people would say, ‘You’re tough graders,’” Ms. Barth said. For instance, Bakersfield—ranked the worst area for ozone in the nation and the second-worst for short-term particulates—suffered a whole month’s worth of days with excessive air pollutants. It was given an F. But even brief spikes and particulates, Ms. Barth said, can lead to significant health impacts, such as asthma and heart problems. To address the issue, the Bay Area Air Quality Management District is offering a $3 million woodstove rebate program to entice people to swap woodstoves for alternatives like heat pumps. The district prioritizes households in high-risk areas, like the valley, or those considered to be low income. So far, 152 homes in Marin either have been approved for the rebate program, are under review or are on a waitlist, said Kellen Dammann, the sustainability marketing and outreach specialist for the Community Development Agency. Mr. Dammann said the program will be open to applications for another three to four weeks, a timeframe given multiple times over the past couple of months. “One reason for this is because people that are currently on the waitlist will sometimes find out they are ineligible or will drop out of the program,” he wrote in an email. The county also has its own rebate program. So far, 29 applications for financial assistance have been submitted. Mr. Dammann surmised that county funds could last a year, unless there is a “run on the bank,” so to speak. For more information, visit baaqmd.gov/grant-funding/residents/wood-smoke-rebate or marincounty.org/depts/cd/divisions/sustainability/green-building-program.