Science & Environment

Study: Wildfire smoke harder on respiratory health than other particulate pollution sources

By Jes Burns (OPB)
March 6, 2021 12:13 a.m.

The past year was a devastating one for wildfire, as several Oregon communities burned during the Labor Day Fires. Oregonians who didn’t experience the fires firsthand still felt them in their lungs as smoke rolled into cities on the west side of the state.

It smelled like a campfire, which might seem preferable to other pollution, like car exhaust. But research out Friday shows just how harmful the smoke situation was. The new analysis finds that the tiny particles in wildfire smoke can be more toxic to humans than particulate pollution from other sources.

A man stops on his bike along the Willamette River as smoke from wildfires partially obscures the Tilikum Crossing Bridge, Saturday, Sept. 12, 2020, in Portland, Ore.

A man stops on his bike along the Willamette River as smoke from wildfires partially obscures the Tilikum Crossing Bridge, Saturday, Sept. 12, 2020, in Portland, Ore.

John Locher / AP

The researchers analyzed 14 years of wildfire, wind pattern and hospital admission data in Southern California.

“We were able to separate out air pollution from wildfire from other sources of air pollution,” said study co-author Tom Corringham of the Scripps Institution of Oceanography in San Diego.

The team found that when wildfire smoke increased pollution levels in a certain area, hospital admissions for respiratory conditions increased from up to 10 times compared to the same quantity of pollution increase from other sources – like vehicle, agricultural and industrial emissions.

The research focused on particulate pollution referred to as PM2.5 – particles so small that they can travel deep in your lungs and be absorbed into your bloodstream. This kind of pollution is regulated by the Environmental Protection Agency, which has established exposure limits to keep people healthy. These are the thresholds used in the Air Quality Index (AQI) that has become so many Oregonians’ constant companion during wildfire season.

“Many people understand that wildfires create more particulate matter than cars or coal-fired power plants do, but the total dose of particles is not the only thing that makes wildfires dangerous,” said OHSU environmental toxicologist Caren Weinhouse, who was not involved in the new research.


Toxicology studies had already shown that PM2.5 created by wildfires is more toxic to humans than other sources. But this analysis marks the first time the effects of wildfire smoke has been quantified in terms of real-world health impacts over a long period of time.

Even though the research was based on wildfire smoke generated from burning vegetation types in the Los Angeles/San Diego area, Corringham says the results should be valid in the Pacific Northwest as well.

“We don’t have any reason to believe that there would be significant differences based on vegetation type,” he said. “I think we would expect these results to transfer and to be fairly uniform across the West.”

Currently the EPA regulates all PM2.5 the same, regardless of the source of the pollution. Corringham and his fellow researchers conclude that this approach isn’t sufficient to protect human health. They write that air quality regulations need to consider where the pollution is coming from when setting health limits.

This approach could take the form of a separate and adjusted AQI scale that could be pulled out during wildfire season that accounts for the increased toxicity of wildfire smoke. Under that hypothetical scale, wildfire smoke would trigger health warnings at lower levels than what we see now.

Such a shift could improve public health in the Northwest as human-caused climate change lengthens fire seasons in the region.

“Wildfires are increasing in frequency and intensity, especially in the Pacific Northwest, so health problems that occur more frequently due to wildfires are going to become increasingly important.” Weinhouse said.

In addition to expectations of increasing smoke from wildfires, Oregon is currently looking to expand the use of prescribed burning outside of fire season to reduce forest fuel loads and wildfire risk. The EPA is seeking public comment on the changes to the state’s Smoke Management Plan through March 22.

The research in Southern California didn’t look at smoke created during prescribed burns, but author Corringham says their work shows there will always be trade-off between risk reduction for wildfire and human health.

“Overall there may be less damage from controlling fuel growth with these prescribed burns than just letting it get out of hand and having these major conflagrations that last for days on end,” he said.

The research is published in the journal Nature Communications.