Scientists want you to know there’s just no way wildfire smoke is good for your health

This story is part of In the Line of Fire, a series from The Narwhal digging into what is being done to prepare for — and survive — wildfires.

When Sarah Henderson began her doctorate in environmental epidemiology at the University of British Columbia, she planned to study how Canadian oil refineries impact air quality and the implications for human health. 

But in the summer of 2003, the Okanagan Mountain Park fire ripped through Kelowna, forcing 27,000 people to flee their homes. The fire destroyed 239 houses and smothered southern British Columbia in smoke. At the time, there was little research on how wildfire smoke impacts air quality — and how exposure to smoky air affects human health. 

So Henderson, who has a background in environmental engineering, changed the focus of her studies.

She did her PhD thesis on how the 2003 wildfires in B.C.’s southern Interior impacted air quality and has been studying the health effects of wildfire smoke exposure ever since. Today, she’s the scientific director of the BC Centre for Disease Control’s environmental health unit. 

“Even though the risk for any individual is small, because everybody has to breathe the air, those risks really pile up in the population,” Henderson said in an interview with The Narwhal.

Wildfire smoke may increase risks of dementia, heart disease and more

Wildfire smoke has three main ingredients. There are gases, such as carbon dioxide and sulphur dioxide, and volatile organic compounds, like benzene, toluene and butene. There is also particulate matter, which can include soot, dust, pollen and spores, as well as chemical particles. The particles are classified according to size and fine particulates — the really tiny ones, less than 2.5 microns in diameter and typically referred to as PM2.5 — pose the greatest threats to human health because they can travel deeper into the lungs than larger ones.

The more particulates in the air, the hazier it becomes. Extremely poor air quality due to wildfire smoke is hard to ignore, often resulting in new reports and public health warnings to stay indoors and take precautions. 

Research by Henderson and other scientists suggests even moderate levels of wildfire smoke can pose significant health risks, especially for people with chronic lung diseases like asthma or emphysema that make them more vulnerable to negative health impacts. Fine particulates found in smoke and other types of air pollution have been linked to damage in several organ systems, including the heart, brain and reproductive system. 

For example, research released at this year’s Alzheimer’s Association international conference found the risk of developing dementia following exposure to fine particulate matter from wildfire smoke was higher than the risk posed by other sources of air pollution, even when the exposure to wildfire smoke was less intense.

“Exposure to non-wildfire PM2.5 raised the risk of dementia diagnosis, but not as much as wildfire smoke,” the researchers concluded, noting it could also raise the risk of heart disease, asthma and low birth weight.

“There’s no way in which it’s good for you; it’s only bad for you,” Henderson said of wildfire smoke. “It’s not something to panic about, but it is a form of air pollution that can affect your health and the more you reduce your exposure, the more you protect yourself, both in the short term and long term.”

Most air quality advisories in Canada are now the result of wildfires, not other pollution

In 2023, Canada experienced the most destructive wildfire season ever recorded, with about 6,550 fires burning more than 184,900 square kilometres between April and October. The fires prompted evacuations in 200 communities from B.C. to Nova Scotia, including the Northwest Territories capital of Yellowknife, home to 20,000 people. 

On average, Canadians experienced eight days of poor air quality due to the 2023 fires, according to the science journal Nature. Some Canadians spent more than half their summer breathing air heavily contaminated by wildfire smoke. 

Wildfires are now the most common reason for air quality advisories, which are issued when concentrations of particulate matter and hazardous gases rise to levels that can negatively impact human health.

To help Canadians understand the health risks stemming from current air conditions, authorities use the Air Quality Health Index (AQHI), a colour-coded scale of one to 10 (with a plus sign if it’s off the charts), based on concentrations of ozone, particulate matter and nitrogen dioxide — the pollutants found to have the greatest health impacts. 

The higher the health index score, the greater the risk and the more precautions people — especially those with health conditions that make them vulnerable to poor air quality — may need to take to stay safe and comfortable. Avoiding polluted air by staying inside and using air purifiers is the most effective protection but avoiding strenuous outdoor activity and wearing a respirator can also help.

“We really need to build a culture of encouraging people to consider protecting themselves from those smoke exposures whenever smoke is affecting air quality, not just when things are orange and awful,” Henderson told The Narwhal.

Small amounts of wildfire smoke also come with long-term health risks

While it’s reasonable to assume wildfire smoke is bad for your health, pinpointing specific health risks from wildfire smoke exposure and separating them from the impacts of other types of air pollution — such as those from vehicle or industrial emissions — is not easy.

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At the University of British Columbia, physician Chris Carlsten is leading an effort to shed light on how wildfire smoke affects human health over the short and long term. His team was recently awarded a federal grant to support its work.

Carlsten said the team is focusing on chronic exposure to any amount of wildfire smoke versus acute exposure to high levels, even though the short-term peaks are “problematic.” 

“There may be more health effects, ultimately, from the more common but lower-concentration exposures,” Carlsten said in an interview. The team will also explore how wildfire smoke affects people differently based on age, sex, genetics, exercise habits and socioeconomic status.

Better data will help improve public health policy and planning when wildfires flare, allowing people to make more informed choices about how to reduce their risk. 

Carlsten said researchers and public health officials have to “walk the line” between ensuring people are adequately informed and “excessive, intimidating and frightening messaging.”

“I think we already have a ton of data — a ton of appropriate and helpful data,” he told The Narwhal. “The bigger gap … is understanding how the population thinks and processes information, what’s important to them and giving them the information [they need].”

Offering people too little information risks failing to communicate the severity of a situation but too much detail can result in people tuning out, panicking or just failing to retain much, according to Cathy Slavik, a postdoctoral fellow at the University of Oregon’s Center for Science Communication Research who studies ways to improve communication about environmental health risks.

“As scientists, we often think that we need to share lots of information; we need to help people understand how we know what we know and what we don’t know,” Slavik said in an interview. “But oftentimes that isn’t actually super helpful for people who just want to know if they’re at risk and what they can do to protect themselves. … It might sound a little bit reductionist, but it’s true that most people will only remember the gist of what you tell them.”

Scientists are testing ways to communicate the message about risks

Figuring out the best way to communicate information about health risks — which often involves complicated and technical information — is challenging.

“We don’t necessarily always know what is the most effective way to communicate a particular kind of risk about a particular kind of hazard,” Slavik said.

Slavik and her colleagues at the centre recently set out to test how effective the U.S. Air Quality Index and Canadian Air Quality Health Index are at communicating the risk of wildfire smoke to parents. 

“One of the really most important aspects of crafting effective communications is testing them and unfortunately, we don’t do enough of that,” she said.

The two indexes broadly communicate the same thing — concentrations of hazardous gases and particulate matter in the air — but the Canadian index was designed to help people better understand health risks stemming from air conditions. It uses a one to 10+ scale while the U.S. index uses a zero to 500+ scale.

Study participants were shown infographics — either linear scales or gauges — representing various levels of air quality compromised by wildfire smoke. Researchers found intense smoke levels sparked similar levels of concern among participants — all of whom were parents — regardless of how the information was presented visually. 

But moderate concentrations of wildfire smoke were a different matter: participants who saw infographics based on the Canadian index reported being more concerned about the impact poor air quality could have on their kids and had stronger intentions to take action to protect them. Their reactions “more closely resembled those parents who had seen the infographics of high levels of smoke,” Slavik said.

The results indicate the Canadian index might be a better tool to help parents better understand that even moderate levels of wildfire smoke exposure can be hazardous to children’s health.

These days, new tools mean anyone can monitor and track air quality 

Advances in technology are making it easier to measure air quality where it affects people most — at home.

Until recently, air quality reports in Canada have been based on data gathered “at a finite number of government-run air quality monitoring stations in Canada using very expensive instrumentation,” Henderson told The Narwhal.

Government monitoring stations equipped with highly accurate $30,000 sensors can be dozens or even hundreds of kilometres away from the communities they were developing advisories for. Meanwhile, low-cost sensors can measure particulate matter concentrations almost as accurately as the government’s monitoring equipment — and at one-tenth the price tag. 

“We now have hundreds of these sensors running in places across Canada, especially in more remote areas, Indigenous communities — places where there were no big, expensive government centres,” Henderson said.

Even communities that are quite close together can be impacted very differently by nearby fires, because of wind and other atmospheric conditions, Peter Jackson, an atmospheric science professor with the University of Northern British Columbia’s geography, earth and environmental sciences department, said in an interview.

Jackson has become the face of a made-in-Canada effort to improve local data about air quality.

In 2023, he led a team of researchers, in partnership with Environment and Climate Change Canada, to launch the AirQuality map, which displays hourly data pulled from both government monitoring stations and hundreds of low-cost sensors installed at peoples’ homes. 

“By putting both kinds of data on the same map, we could evaluate in real time how the low-cost monitors compared with the regulatory monitors,” Jackson said.

The map now includes an overlay that shows where wildfires are burning and predicts where smoke will be blown. Jackson said the hope is to expand the map to cover more of North America and to allow its algorithm to update more quickly to reflect changing conditions.

As Canadian summers get drier and smokier, the air quality map and tools like it can help people prepare for wildfire smoke events, both moderate and intense.

“This is our lives now in British Columbia, and the more we can raise the bar on communicating about air quality and its risks, the better off the whole population is going to be,” Henderson said.