Record setting conflagrations in California and Colorado have smothered residents of the two states with choking, stinging smoke. But the impact of that smoke is also being felt hundreds, even thousands, of miles away, and the health impacts may last for years after the flames subside. 

If the current fire weather trends continue, said Pete Lahm, a smoke specialist for the U.S. Forest Service, “it’s gonna be a hellacious level of smoke out there for a lot of people.”

Smoke from the current fires has blanketed much of the United States, spreading all the way to the East Coast, although not always falling to the ground level where people can inhale it. Colorado has four large wildfires of its own burning, including one on the verge of becoming the state’s largest in history. But much of the smoke around Denver last weekend was from the fires in California, said Colorado state air quality meteorologist Scott Landes.

“I would say at minimum 50 percent of the smoke that we’ve had in the Denver area has come from the California wildfires,” he said.

Doctors have long warned that the smoke from wildfires can damage the hearts and lungs of people who are near the flames. But they are increasingly learning that such emissions may damage livers and kidneys, hobble immune systems and even prompt genetic changes that could be passed down through generations. And with climate change continuing to drive steep increases in the amount of land burning around the planet, millions more people are expected to endure smoke-related illnesses in coming years.

‘Every Fire is Different, So Every Smoke is Different’

Understanding the health impacts of wildfire smoke has proved more challenging than those from other forms of air pollution. Such smoke is more difficult to monitor than emissions from factory smokestacks or highways full of tailpipes, which rarely move or change their fuels. Wildfires, in contrast, spew smoke from different locations every day, and turn everything from dense forest canopies and grasslands to underground peat and residential developments into an ever-changing cocktail of particles and gases. 

Blazes that produce a wisp one minute can pump out plumes dark enough to turn on streetlights the next. Smoke that towers over mountains at noon can flood valleys when the atmosphere cools after sunset, or persist in the stratosphere for weeks before coming down hundreds of miles away.

“Every fire is different, so every smoke is different,” said Ana Rappold, who studies the health impacts of air pollution for the Environmental Protection Agency. “That’s very difficult to study from an epidemiologic perspective.”

After a 2008 blaze near her office in North Carolina, Rappold and cardiologist Wayne Cascio studied emergency room records that showed not only a steep increase in people hospitalized with breathing difficulties but a spike in cardiovascular ailments.

“It was a peat fire and it really smoked out to the community,” she recalled. “We found ourselves really unprepared.”

In a subsequent study, Rappold and Cascio, who is now the Director of the EPA’s Center for Public Health and Environmental Assessment, compared Medicare records and smoke exposures in every county in the nation outside of Alaska over a five year period. They hunted for specific outcomes like asthma, cardiovascular disease and respiratory problems. Short-term smoke waves, they found, prompted breathing difficulties in patients over 65 that led to premature deaths and hospital admissions costing some $63 billion. Even barely visible smoke showed substantial health impacts.

“Smoke that travels far, it’s in very small concentrations,” she said. “But it’s enough.”

And the health impacts of wildfire smoke are proving longer lasting than was thought even a few years ago.

After Missoula, Montana, was smoked out for much of the summer of 2017, a team from the University of Montana’s School of Pharmacy visited the town of Seeley Lake, which was overwhelmed with wildfire smoke for nearly 50 days. The researchers had residents there breathe into spirometers—devices that measure lung function—immediately after the fires and then again, one and two years after the fires. They found that the respiration of subjects in the study was significantly worse a year after the fires than it was right after weeks of breathing the heavy smoke. Even after two years, the lungs of many of the people had not recovered the same breathing ability they had just after the smoke wave had passed.

“It’s not something that we’ve ever seen,” said Sarah Coefield, an air quality specialist for the city and county of Missoula. “The general understanding of smoke exposure was, ‘It’ll be bad, but then you’ll bounce back.’ That’s the line we’ve told people for years.”

Smoke’s Microscopic Hazards Can Travel Thousands of Miles 

Smoke from burning forests and grasslands can contain everything from carbon monoxide to carcinogens like benzene and formaldehyde, but the two things that health officials focus on are ozone and particulate matter, both of which can travel thousands of miles from the fire that creates them.

“Wildfire smoke is made up of thousands of compounds and you know, most of them are nasty for our health, but for protecting public health, we’re most concerned with fine particulates,” said Landes, the Colorado air quality meteorologist, “and we’re most concerned with ozone.”

Particulate matter less than 2.5 micrometers in diameter—about a quarter the size of a particle of dust or pollen—is known as PM 2.5. Long-term exposure to air with even moderate concentrations of it can stress the heart, increase the buildup of plaques inside arteries, hinder liver function and increase the risk of heart attack, stroke and kidney disease. 

Even short-term exposures can prompt an inflammatory response in the body and hobble its ability to fight infection, leading to increased hospitalizations for asthma and pneumonia during fire season and, according to research published this summer by the University of Montana and the U.S. Forest Service, more severe flu seasons afterwards.

Such studies documenting how PM 2.5 increases lungs’ susceptibility to later respiratory illnesses have added to concerns that people exposed to wildfire smoke, especially firefighters, could have increased vulnerability to Covid-19 that would persist long after the smoke cleared.

The PM 2.5 in smoke can have effects not only in the communities closest to a fire, but for people living in areas long distances away. 

“Fine particulates can travel thousands of miles, as we saw this past weekend,” Landes said of the PM 2.5 that arrived in Colorado from the California fires. “And with the fine particulates, they get lodged in your respiratory system. They get into your bloodstream. People with heart or lung disease really suffer and when particulates get high enough, everybody suffers.”

Ozone from wildfire smoke can also present health risks far from the site of the blaze. The gas is often created by chemical reactions in the smoke as it is exposed to light and heat, and ages and decays while drifting away from the fire. It can then fall to the ground a thousand miles or more from the flames in which the smoke was born.

In some corners of the West, smoke from distant fires has offset the air quality improvements brought by regulation of smokestacks and tailpipes.

“If you look at some of the ozone concentrations here in the front range, from Denver down to Colorado Springs, we are seeing some of the highest ozone concentrations we’ve had in years,” Landes said, noting the spike has offset regulatory efforts to throttle down emissions of the pollutant from human sources.

“A lot of the good work that we’re doing to try to decrease the amount of anthropogenic emissions, wildfire smoke can kind of wipe all that out in one summer,” he said, referring to emissions stemming from human activities.

San Francisco is Choking

Although its reach is widespread and long-lasting, the smoke from the California fires is affecting Bay Area residents most severely.

Although ringed by fires, San Francisco is largely protected from the flames by dense development. But a week after more than 11,000 dry lightning strikes sparked fires throughout central and Northern California, including the second and third largest fires in state history, San Franciscans can hardly breathe. On Tuesday morning, winds blew smoke from wildfires in the Santa Cruz mountains north into the city, and air quality quickly reached unhealthy levels. The air assaults the eyes, throat and lungs like sooty gray tear gas. On some days the Bay Area air quality has registered as among the worst in the world. 

The fires in the Bay Area remain largely uncontained and health officials have advised those sensitive to respiratory issues to stay indoors with the windows closed. Even for a healthy person, 30 minutes outside can be enough to induce a headache. 

The smoke has robbed city residents of their main refuge against coronavirus lockdowns—daily walks—and has shut down outdoor dining, a lifeline for restaurants forced to close their dining rooms to halt the pandemic. Beyond curtailing already limited engagement with the outside world, however, the bad air raises fundamental questions for California, where fires are burning across more than 1.4 million acres before the fall fire season—historically the state’s most deadly and destructive time of year—even begins.

“This has been such a short, but very significant punch in smoke,” said Pete Lahm, the Forest Service smoke specialist. But “it’s still not in the realm of 2018, 2017 and 2008—the worst of all those years.”

That year, he said, lightning started fires in June that burned through the summer. “When they go a long duration, they really make a big effect,” he said. Fire weather forecasts show little to keep the current fires from burning for months, and possibly matching the amount of smoke from those previous years. The most recent wildfire forecast from the National Interagency Fire Center in Boise, Idaho, reports the weak summer monsoon and potential for delayed rains and strong offshore winds in October and November could create high fire danger in California right through the autumn.

San Francisco residents are wondering what breathing in the smoke means for their health. Can they be impaired by wildfire smoke the way a person can be sickened by second-hand cigarette smoke? Are the effects cumulative? If so, is living in an increasingly smoky California hazardous to one’s health?

“There is still much that is unknown about the long-term consequences of exposure to air pollution,” said Elizabeth Muller, co-founder and executive director of Berkeley Earth, a non-profit organization focused on land temperature data analysis for climate science.

When a wildfire wiped out the Northern California town of Paradise two years ago, smoke from the fire settled in Sacramento, 90 miles away. Muller’s lab found that the air quality there was as unhealthy as smoking 10 cigarettes a day.

Muller also noted that the smoke from the current fires isn’t the worse she’s seen. “But it’s still bad,” she said. “A bigger issue right now is how incredibly widespread the unhealthy air is, covering much of California.”

Ann Hobbs, associate planner for the Placer County Air Pollution Control District that extends from the Sacramento Valley up into the Sierra Nevada mountains, suggests that people who have the space to do it establish a “clean room,” where the smoke is filtered from the air and everyone in a household can fit comfortably and stay cool.

“One of the real big issues with wildfire smoke is you can’t escape it,” Landes said. Fine particulates, he said, are so tiny, “they can work their way under your door and through the cracks in your windows. It can get into your house.”

A portable air cleaner, or an air conditioner with a MERV 13 filter capable of screeming out nearly all fine particles, is critical to maintaining clean air inside, but only a first step, said Coefield, the Missoula air quality specialist.

“There’s so much that goes into creating a cleaner indoor airspace,” she said. “It’s not even just putting on a better filter. There’s more to it than that.”

Preparing for a Fiery, Smokey Future

And it isn’t just residents of the “Smoke Belt” that includes the Pacific Coast and the Great Plains who will need to prepare for more smudged skies and hacking coughs from wildfire smoke. The most recent National Climate Assessment anticipates the warming and drying climate will bring the U.S. three times as many large fires by the middle of the century.

That’s already happening in California. Research by Park Williams, of the Lamont Doherty Earth Observatory at Columbia University, published last year in the journal Earth’s Future, showed that California’s fivefold increase in acreage burned by wildfires between 1972 and 2018 was probably driven by a 1.4-degree Celsius increase in the temperatures of the state’s hottest days.

A 2016 study by researchers at Harvard, Yale and Colorado State University, predicts that, over six years around 2050, 82 million people in the West will endure more “smoke waves,” which they define as two or more days of heavy wildfire emissions, with smoke that will be both thicker and longer-lasting than today. Other Colorado State research shows the number of U.S. residents dying annually as a result of exposure to wildfire smoke could more than double, to 40,000, by the end of this century.  

But many of the impacts of an increase in U.S. wildfire won’t be delayed until later this century, or isolated to the West.

This month’s fire potential forecast from the National Interagency Fire Center shows that, as California’s fire weather finally declines this fall, high wildfire danger will spread across the southeastern United States, from Texas to Pennsylvania.

“I’ll be honest, I don’t remember it being quite as wall to wall red,” Pete Lahm, the Forest Service air quality specialist, said, looking at the map of the coming fire danger.