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Smoke from faraway wildfires may be worse for Coloradans than if it came from blazes in their own backyards

Some initial studies have shown that long-range smoke may be more toxic and since one of its characteristics is that its smoky smell disappears, it is sneakier.

Smoke from wildfires in California, Oregon and parts of Utah settled into the Vallecito Valley in southwest Colorado in early September 2020.(Jeremy Wade Shockley, Special to The Colorado Sun)

For long stretches of the summer the Front Range has been bathed in smoke traveling hundreds of miles from California and Oregon wildfires and it turns out that long-range smoke could be more dangerous than the fumes from homegrown forest fires.

Some initial studies have shown that long-range smoke may be more toxic and since one of its characteristics is that its smoky smell disappears, it is sneakier.

“We don’t necessarily put it together that these fires create an emergency, but we have a silent epidemic,” said Sheryl Magzamen, an associate professor at the Colorado School of Public Health.

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Driven by climate change, the frequency and intensity of wildfires have been increasing in a hotter, drier West. The number of seasonal wildfires doubled between 2008 and 2015, and whether they are in California or British Columbia, some of that smoke can find its way to Colorado.

“This is really the big issue,” said Dr. Anthony Gerber, a researcher on lung disease at National Jewish Health. “It used to be that we had a few days of high ozone or high particulates. Now we have weeks on end of smoke. You start to change the equation from short-term effects to long-term, potential increases for lung disease, cardiovascular disease.”

Studies have found that long-term wildfire smoke has had an impact in Colorado in asthma, pregnancies –  playing a role in an increase in preterm deliveries and gestational diabetes in mothers – and hospitalizations for cardiovascular disease.

It all starts with the nature of the smoke heading our way.

First, it depends on what’s burning. When the Bootleg fire in Oregon burned through the woods of the Fremont-Winema National Forest, it sent up one kind of smoke. When the California’s Dixie fire tore through the town of Greenville, razing buildings and cars, it sent up quite another.

Firefighters working hard to protect homes in Greenville, California, after extreme weather conditions resulted in aggressive fire behavior in the Dixie fire earlier in August. (InciWeb)

Even a fire burning through forest is a complex creator of smoke with the heat from the flaming portion of the fire “boiling” the trees ahead, not yet burning, pulling water and chemicals from them into the flames. At the same time, it is sucking smoke from the charred but not completely burned forest left in its wake.

“All these processes are happening at the same time … flaming, boiling and smoldering,” said Frank Flocke, a researcher at the National Center for Atmospheric Research.

There are two basic elements in smoke: gases and aerosol, which is composed of particles. The chemical composition depends upon the burning conditions, and gases and particles continually interact, with some components shifting between the two as the smoke drifts away and reacts with the atmosphere.

A smoldering, lower temperature fire will produce less nitrogen oxide and relatively more volatile organics and primary particles. The hotter the fire the more nitrogen oxide and a smaller ratio of volatile organic chemicals.

Over time a second group of nitrogen compounds can form, which can be more toxic. Meanwhile, some of the toxic chemicals found in the emissions at the fire, such as acrolein and benzene, will be wiped out in chemical reactions.

Two chemicals that drop out are guaiacol and cresol, which together gives smoke its smoky smell, even as the rest of the smoke moves on.

“You can’t say that smoke becomes more toxic or less toxic,” Flocke said. “It depends. It is complicated.”

Frank Flocke, a scientist in the Atmospheric Chemistry Observations & Modeling Lab at the National Center for Atmospheric Research, outside his facility in Boulder on April 21. (Andy Colwell, Special to The Colorado Sun)

Another determining factor in the composition of the smoke is moisture, which affects the temperature of the fire. In the smoke itself the presence of water enables some of the heavier molecules, such as heavy metals, perhaps from a car burning in Greenville, to attach themselves to the aerosol particles.

As the aerosol travels to the Front Range, a two- to three-day journey, a lot of things happen. The particles can grow or partially evaporate and are bleached by absorbing sunlight which changes their composition.

PM 2.5 continues to be a major culprit

The greatest health risk comes from microscopic particles – 2.5 microns in size known as PM 2.5 – that can penetrate the lungs and cross into the bloodstream. The width of a human hair is about 70 microns.

Preliminary laboratory studies by Greek researchers – Greece has also been racked by wildfires with 2,000 people evacuated from the island of Evia earlier in August – estimate that through oxidation, the particles can become more toxic.

Laboratory experiments in a smoke chamber, by Athanasios Nenes, a researcher at the Center for Studies in Air Quality and Climate Change in Patras, Greece, showed that the smoke became more toxic over time, generating oxygenated and nitrated hydrocarbons.

“Many of the oxidized compounds can also have a carcinogenic and mutagenic effect, which leads to chronic toxic responses,” Nenes said in an email.

One study found that over 68 hours ambient smoke, again from Greek wildfires, had become about two times more “reactive.”

These studies are preliminary, but point to a troubling prospect, said Dr. Mary Prunicki, director of air pollution and health research at Stanford University’s Sean N. Parker Center for Allergy and Asthma Research.

“It looks that as smoke ages it produces more free radicals which are bad for the body,” Prunicki said. Though she cautioned that wildfire smoke is so variable and difficult to measure that it is difficult to make generalizations.

In her own work, Prunicki is looking at the impact of wildfire smoke on the immune system, which appears to become “deregulated” with a decrease in good cells and an increase in inflammatory cells.

And the implications? “It’s all bad,” she said. “That is why we have to get on dealing with climate change and develop preventative measures for people to avoid smoke when we know there are going to be bad wildfires.”

National Jewish’s Gerber said that the particulates are inflammatory and for people who are genetically susceptible, the constant breathing in of particles could lead to chronic lung disease.

There is the possibility that at the cellular level particulates could change proteins. “It would be like steel getting rusty,” Gerber said, “a reaction that causes a little bit of damage.” 

Smoke with toxic heavy metals could create ‘“oxidative stress” that could cause damage over time, Gerber said.

“As long as it is a one- or two-off exposure, you’re fine,” Gerber said. “These long-term exposures could cause possible changes in protein or gene expression.”

Heavy smoke sweeps the view on a highway outside Paonia on Aug. 7. The fine particles blew into western Colorado from the wildfires in California and Oregon. (Hugh Carey, The Colorado Sun)

Smoke from fires further west usually makes its way to Colorado through Wyoming and then drops south from Fort Collins to Denver.

“Most of the time when we’ve gotten smoke in the greater Denver region from out of state it comes by Wyoming, the mountains are lowest there, and avoids the big peaks in the Rockies,” said Jeffrey Pierce, a Colorado State University air pollution researcher.

The result is that the Front Range, including Fort Collins, experiences the highest wildfire smoke PM 2.5 concentrations, with the metro Denver area experiencing higher concentrations relative to the southern half of the state.

But on Aug. 7, smoke from California “made a beeline over the Rockies,” Pierce said. “It took the fast route and covered all the big peaks.”

PM 2.5 particulates on the Front Range that day were measured at 100 micrograms per cubic meter, about three times the daily federal health standard and almost 10 times the amount deemed safe to breathe in on a daily basis over the course of a year.

The impacts from long-range and long-lived wildfire smoke are already being detected in Colorado.

Researchers from the Colorado School of Public Health and CSU matched the outcomes in 536,000 Colorado births between 2007 and 2015 with levels of wildfire smoke, adjusted for other air pollutants such as ozone, and found higher smoke levels affected both the baby and mother.

Exposure to wildfire smoke in the second trimester or over the entire pregnancy was associated with preterm births. (Exposure limited to the other trimesters didn’t show the effect).

Among the effects observed for pregnant women were positive associations between exposure and gestational diabetes and gestational hypertension.

“What we are seeing is probably the stress the smoke is putting on the mother’s respiratory system and the baby not getting as much oxygen,” said James Crooks, a researcher at the School of Public Health and National Jewish, who co-authored the study. 

“It is similar to what you’d see with a mother who smokes,” he said. “Smoke doesn’t just affect the lungs …it affects other organs and metabolism.”

“It is important to make obstetricians and pediatricians aware that there is this link and help moms to mitigate their exposure, spending less time outside on smoky days, using home air filters, and N95 masks if you are close to a fire,” Crooks said.

Exacerbating the problem, Crook said, is the fact that Front Range PM 2.5 peaks are getting bigger and one of the reasons is long-range wildfire smoke. “A significant fraction of smoke in Colorado comes from smoke transported from the U.S. Pacific Northwest and Western Canada,” the study said.

A six-year study of wildfire smoke on the Front Range, from Fort Collins to Colorado Springs, found a 10 microgram increase in PM 2.5 per cubic meter was linked to an increase in hospitalizations for respiratory diseases such as chronic obstructive pulmonary disease, asthma and acute bronchitis.

A 10 microgram increase in PM 2.5 is enough to take the Air Quality Index from a midrange reading for moderate air quality, 26 micrograms, to an unhealthy reading.

Studies have also found that increase in this fine soot was also associated with heart failure and cardiovascular-related hospital admissions.

One of the provocative aspects of the study, which was led by the Colorado School of Public Health’s Magzamen, was the ability to look at the difference between homegrown Colorado wildfire smoke and long-range wildfire smoke.

The researchers looked at two years: 2012, which was marked by early season local fires including the Waldo Canyon fire near Colorado Springs and the High Park fire near Fort Collins, as well as late season where the smoke came from fires in the Pacific Northwest, and 2015, when smoke was primarily from fires in the Pacific Northwest

In 2015, the late fire season showed an increase in asthma hospitalizations. When split between early season and late season, asthma hospitalizations were only significantly elevated during the 2015 late season, when the Front Range experienced long-range transport of smoke.


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