March–April 2024


Burn Notice

Wood smoke pollutes—but you can help by burning cleaner.

Keith Goetzman

Dancing flames, a warm glow, and the sweet tang of wood smoke in the nose put many Minnesotans in their happy place. And in recent years, the booming popularity of backyard fire pits has meant more of us than ever are enjoying the ambience of recreational fires. In fact, the most recent survey of wood burning across the state by the Minnesota Pollution Control Agency showed that the top reason Minnesotans now burn wood is for recreation.

Those fires, as alluring as they are, come with an environmental cost. Because 57 percent of the state’s direct fine particle emissions are from wood burning, these small fires are collectively a significant and increasing contributor to air pollution, says Tyler Ellis, neighborhood air pollution control lead for the MPCA.

The aromatic scent of wood smoke carries with it a complex mix of fine particles that, because they’re so small, can affect human health, Ellis explains. “Short-term exposure can aggravate lung disease or acute lung issues and can trigger asthma attacks,” he says. “Long-term exposure is associated with chronic diseases. And in high concentrations, wood smoke and fine particles can damage lung tissue.”

Oof. Sounds bad. What can be done? Well, Ellis suggests that no one needs to stop having a good time around campfires.
“We don’t want to be the fun police. We’re not telling people ‘Never burn ever,’” he says. “What we’re focusing on is getting people to use best practices when they do burn.”

What does that mean? For starters, burn only dry, seasoned wood that’s been stored out of the elements. Optimal dryness, he explains, is between 10 and 20 percent moisture content, measurable with a moisture meter that’s available at hardware stores for under $20.

Also, use a metal fire ring or one of the new types of “low smoke” fire pit devices that contain and concentrate the heat, and don’t oversize your fire. In tests with various types of recreational burning—including in the steel fire rings that are a fixture in Minnesota state park and state forest campgrounds—the MPCA learned that properly built, properly sized fires in these scenarios had lower emissions than open fires.

People who burn wood to heat their homes can also cut their emissions. The MPCA’s survey showed that one-third of Minnesotans who use a wood-burning furnace or stove are using a model made before 1989. “The post-1989 EPA-certified stoves use technologies to ensure that there’s secondary combustion, so emissions, especially fine particle emissions, are reduced quite a bit,” says Ellis.

Overall, wood burning has been increasing over the course of the survey’s history, which began in the 1960s. So the more Minnesotans who learn to burn clean, the better off our air quality will be—for you, for your neighbors, and for everyone who lives downwind.