Editor's Note: In the run-up to the new year, Crosscut is sharing ten days of its best stories from 2011, each with a different theme. Today we revisit coverage about the environment.

This story, by Robert McClure and Katie Campbell, first appeared December 16. 

The warning label on the wrapping of neatly split firewood is one we're more accustomed to seeing on cigarettes or heavy-duty chemicals — “known… to cause cancer, birth defects, or reproductive harm."

But in fact, heart attacks, strokes, high blood pressure, asthma attacks, and premature death – in addition to cancer – are all linked to wood smoke pollution. It’s a finding that poses a vexing dilemma for poor and rural communities around the Northwest, where wood is a cheap or even free source of heat.

And in Tacoma, where the air is so dirty it violates the Clean Air Act, authorities are gearing up for what promises to be an arduous and expensive campaign, over the better part of a decade, to clean up wood smoke pollution. It’s an effort that already has some residents chafing at government interference, and one that will set the stage for policy in other Northwest communities when they bump up against tightened federal pollution standards.

In Tacoma and many other towns across the Northwest, wood smoke is the prime culprit in driving spikes of sooty, toxic air pollution that leave some residents — particularly asthmatics, kids, and the elderly — gasping for breath. It’s especially bad during sunny, cold stretches like those we’ve seen in recent weeks, because atmospheric conditions trap the pollution close to the ground.

Along with fireplaces and other wood-burning heaters, old wood stoves produce about half the microscopic particles of soot that typically hang in the air when winter air stagnates. (By comparison, industry — already heavily regulated — emits just one-tenth of the Tacoma-area soot pollution.)

In Washington, the state Ecology Department estimates that sooty pollution from sources including wood smoke and diesel exhaust contributes to 1,100 deaths and $190 million in health costs annually.

The department says a conservative estimate of the annual number of deaths attributable to soot pollution in Pierce County alone is 140.

The toll in everyday suffering is less easily quantified. But Nancy Gregory, an asthma sufferer who lives southeast of Tacoma near Spanaway, is typical. She says she dreads having to go outside when the winter sky turns blue and air-cleansing rains stop.

“When I walk out to the mailbox, I come back in and sometimes I’m wheezing and I have to go to my inhalers. It makes it hard for me to breathe,” said Gregory, 70. For her husband Bryan, 73, it’s even worse. He has chronic obstructive pulmonary disease and must breathe from an oxygen tank most of the time. When winter weather turns nice they try to stay inside — but eventually they have to buy groceries and go to doctor’s appointments.

“If he gets a coughing attack, he needs a chair,” Gregory said. “We can’t just let him be walking. He needs something to hold himself up on.”

Restricting the use of the wood stoves that heat so many homes across the Northwest is a difficult proposition though, because many people can get wood for cheap or free, and using a wood stove can greatly reduce electricity and natural-gas bills that run wild in the winter. Installing a new clean-burning stove typically costs $2,000 or more — and many argue that it’s lousy timing to launch an expensive campaign to clean the air; federal standards or no federal standards.

Yet that’s the recommendation of a task force representing local governments, industry, the military, and others involved with soot pollution levels in and around Tacoma. Last week the group voted to recommend removal of all wood stoves that don’t meet current government standards by 2015, in the area violating the Clean Air Act.

“It scares me,” said Gretchen Smith of Puyallup, whose family spends about $380 a month on electricity, including baseboard heaters, even when they use wood heat as a supplemental heat source.

”Most of us are just hoping our cars won’t break down and the fridge won’t go out or we don’t have a medical crisis. … We don’t have much wiggle room in our budget.”

The Smiths’ wood stove, manufactured before federal rules required large increases in efficiency and decreases in pollution, is one of an estimated 24,000 old, heavily polluting wood stoves spread across the area violating the federal law, which includes most of Pierce County, from near Orting to Steilacoom to Commencement Bay.

Other Pacific Northwest communities, including Klamath Falls and Oakridge in Oregon, the Cache Valley of Idaho, and Libby, Montana, are also in violation of the federal Clean Air Act’s rules on soot.

And Washington officials say Yakima, Darrington, Marysville, Vancouver, Wenatchee, and Clarkston are at risk of violating the federal soot standards too.

“We have a number of communities getting up around those [violation] levels and they’re all dominated by wood stoves,” said Stu Clark, manager of the Department of Ecology’s air-pollution program.

Kent, Everett, Olympia, Port Angeles, Spokane, Lynnwood, Mountlake Terrace, Lake Forest Park, and south Seattle have also struggled with high soot pollution levels, much of it thought to be traceable to burning wood.

The problem that Tacoma faces today from wood smoke is likely to be a growing problem across the West in years to come, said Jeff Hunt, an air pollution specialist for the EPA’s Seattle-based Region 10. Federal soot standards could be tightened as early as 2012, although it would still be a number of years before they were enforced.

In the meantime, though, health damages mount.

Picture the width of a human hair. Now imagine a speck of toxic-covered dust that is 1/30^th as wide. These are the so-called “fine particulates” — soot — that knocked Tacoma into violation of the Clean Air Act. They mostly come from burning wood, diesel, gasoline, and other fuels. And for susceptible people, they can kill.

Exposure to these particles — over even a few hours — can trigger heart attacks and strokes, according to an expert panel’s report for the American Heart Association in May 2010.

The particles are so small that, not only do they get into the lungs, causing respiratory distress, some also cross over into the bloodstream itself.

Wood smoke isn't the only source of the tiny particles — they also come from truck and car exhaust, ships, dust, industry, and sea salt. But it is the biggest. In the Clean Air Act “non-attainment area” in Pierce County, 53 percent of those particles are estimated to come from burning wood on the winter days when the area violates the federal law.

Those tiny particles of soot are only one of the unhealthy byproducts of wood burning. Others include benzene, a potent carcinogen, and a group of chemicals known as polycyclic aromatic hydrocarbons that are linked to cancer in laboratory test animals. Not only can these hydrocarbons cross the placental barrier in pregnant women, one study suggests prenatal exposure to them tends to lower a baby’s IQ and increase the risk of asthma.

Carbon monoxide is also a byproduct. The poison has been shown to cause chest pain in people with heart disease because it reduces the amount of oxygen delivered to the body and it can cause permanent heart damage.