Tiny Particles from Wildfire Smoke Follow ‘Wind All The Way Down to Your Smallest Air Sacs’

Cathie Anderson

September 19, 2020



The potential health consequences of exposure to wildfire smoke can go well beyond the coughing, sore throats and the watery eyes that most Californians have experienced over the last few weeks.

Just as with viruses and bacteria, tiny particulate matter from these wildfires, undetectable to the human eyes, poses the greatest challenge to people’s health both in the short term and years down the road.

“While the big particles are bad, they may not be quite so bad as the small particles, the PM 2.5,” said Dr. Brian Christman, a national spokesperson for the American Lung Association. “They’re about 1/30th the size of a human hair, and they’re small enough that, when you breathe, they will just follow the wind all the way down to your smallest air sacs and they can lodge in your delicate lung tissues and cause a lot of inflammation.”

There are estimates, he said, that 300,000 premature deaths worldwide are related to poor air quality due to wildfires.

These deaths may be sudden in onset, as when the microscopic particulate matter manages to move into the circulatory system from the lungs’ tiny air sacs. Once in a blood vessel, they can inflame areas of blood vessels already narrowed by fatty deposits called plaque, said Christman, an expert in pulmonary diseases who is the chief of medicine at the U.S. Department of Veterans Affairs Tennessee Valley Health System.

“When these areas develop inflammation, it increases the chance that one of these plaques can rupture, resulting in sudden clot formation and blocking of the vessel,” he said. “In the heart, this is a heart attack or myocardial infarction.”

If such a blockage occurs in the brain, it’s called a stroke he added. With ongoing exposure, he said, the ultrafine particles get even more opportunity to cause inflammation and scarring in the lungs and blood vessels, potentially leading to health problems later in life.

Christman and Dr. Carlos Nunez said that, while there haven’t been periods in history where people have been repeatedly exposed to wildfire smoke, there is plenty of research on how PM 2.5 from smog and other types of air pollution affects people’s health.

“If you live in an area where you have chronic exposure to unhealthy air, whether it’s from wildfires or from smokestacks at factories, smog from automobiles, you name it, we see that our lungs don’t do well when we don’t breathe clean air,” said Nunez, chief medical officer at the digital health company ResMed, “Now instead of worrying about that factory smokestack in your neighborhood, you might have to worry that (you) live in a place where there will be significant wildfires every year. It’s likely that (you’re) going to have several weeks or several months every year of poor air quality.”

Researchers at the University of California, Davis, released a study Thursday showing that, in northern coastal California, the number of high-severity wildfires has been increasing by about 10% per decade since 1984.

They studied coastal foothill and mountain ranges stretching north to the Klamath Mountains and southeast to Berryessa Snow Mountain National Monument and surrounded by Central Valley lowlands to the east. The Berryessa range spans much of nearby Yolo, Solano, Colusa, Lake, Napa, Mendocino and Glenn counties.

Published online in Environmental Research Letters, the UCD research shows that the drought of 2012-2016 nearly quadrupled the area burned severely, compared with the land mass affected by the relatively cooler drought of 1987-1992.

“With climate change, rising temperatures are extending the growing season, but then at the peak of summer, it’s so hot and dry that the exuberant growth turns into kindling for fires,” Christman said.” It’s a tough problem. People living on the coast are a little bit luckier in that there’s a breeze from the oceans that clears out that bad air a little bit faster.”

Christman and UC Davis physiology researcher Kent Pinkerton urged residents to take steps to protect their lungs and circulatory systems from PM 2.5 but also to consider behavioral changes that could reduce the consequences of climate change.

To prevent exposure to particulate matter, remain indoors on days when the air is unhealthy, they said, and if you must go outdoors, wear an N95 respirator. Because of the coronavirus pandemic, they acknowledged, these respirators can be particularly hard to find.

Set auto air conditioning units to recirculate the air already inside the vehicle rather than drawing in air from outdoors, they said. In most vehicles, that button will have the symbol of an auto with an arrow turning around.

Also, they said, change the air filter on home air conditioning unit more frequently as they will clog up faster when the outdoor air is highly polluted. Air filters designed for high-efficiency particulate absorption, or HEPA, will keep out 99.7% of particulates measuring 3 micrometers or larger. Air purifiers with carbon filters, UV lights and HEPA filters will add an extra layer of protection.

Cloth masks help to prevent wearers from spreading their own germs and may reduce the overall load of both viral and fine particulate matter coming into nasal passages, Pinkerton said, but they are not nearly as effective as N95 respirators. To add an extra layer of protection, he said, some people are adding the fibrous blue shop tiles like the ones used by auto mechanics in masks with openings for filters.

Long term, though, Pinkerton said, he hopes more Californians will embrace ways to reduce the burning of fossil fuels. For instance, people could walk, bicycle, or take public transit rather than driving, he said. When air quality is good and outdoor temperatures are mild, open doors and windows to cool homes rather than running air conditioning units.

These measures “may seem a little vague,” he said, “but they actually do represent an active effort on an individual’s part to help counteract the effects of climate change.”

He and other researchers at UC Davis have been closely studying wildfire air pollutants and even comparing them to air samples of the same mass from cities in China that have a comparable geographic nature as the Sacramento region.

Normally, air pollution levels in China are about 10 times higher than they are in Sacramento, but if you look at equal-mass samples from when Northern California has these acute levels of wildfire particulate matter, the Sacramento-area air is far more toxic than the samples from China.

“We’re trying to figure that out, why that could be,” he said. “Some chemists have expressed to us that there’s a lot more oxidated organics (carbon from trees and the like) in the Sacramento area than in China and that might be the reason why we’re seeing acutely a more significant toxic effect.”

The researchers also looked at what happens with repeated exposure to the local and Chinese air samples, Pinkerton said, and in those cases, China’s particulate matter produced significantly greater inflammation. The sample from China that had the largest effect on the lungs was taken, he said, from a region where coal is still burned.


Rebecca Schmidt, one of Pinkerton’s peers at UC Davis, has been working with a team trying to determine how pregnant women and their unborn children will fare after repeated exposure to wildfire smoke. They began that research immediately after the 2017 Napa-Sonoma fires and have continued collecting data on new and existing participants through this year.

The goal, Schmidt said, is to get enough data to draw valid conclusions, and that takes big numbers. Many of these women are in the ideal age range to have children, Schmidt said, and so they’ve had a subsequent pregnancy even as the risk of exposure to wildfire smoke has grown.

Schmidt and her team are following the women and babies through at least one post-natal visit, she said, and they hope to later get funding to do subsequent surveys of participants as they age.

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