Canadian Wildfire Smoke Is Triggering Outdoor Air Quality Alerts Across the Midwestern U.S. It Could Pollute the Indoors, Too

Throughout May, more than 140 wildfires have burned across Alberta and British Columbia. On Sunday, the thick, ashy haze billowing from these infernos drifted across the U.S. border, casting a blanket of smoke over Minnesota and Wisconsin, which eventually made its way to Iowa and other parts of the Midwest earlier Tuesday morning. 

Counties throughout these Midwestern states have issued air quality alerts and warned residents to stay indoors until the smoke subsides. The problem? In many cases, wildfire smoke follows you inside, seeping through the cracks and crevices of a house or building. 

As warmer temperatures and drier conditions fuel more frequent and severe wildfires, an emerging field of research is uncovering the pernicious threat of poor indoor air quality from wildfire smoke. For today’s newsletter, I am parsing this veil of smoke to investigate the ways poor indoor air quality could affect individuals—and how experts are trying to keep indoor air clean.

Polluting From the Outside In: The “dirty secret” of outdoor air pollution is that you are breathing most of it when you’re inside, according to Joseph Allen, the director of Harvard University’s Healthy Buildings Program, where he studies indoor air quality. 

“That sounds wild and maybe even incorrect but it’s right,” Allen told me. He broke down the numbers for me to explain how that works: While a typical older home in the U.S. has about a 50 percent infiltration rate of outdoor pollution air seeping in, the catch is that Americans spend around 90 percent of their time indoors. So even though there are less pollutants inside, people can still be exposed to harmful levels of smoke during a wildfire event, which has been associated with a slew of health risks, from cardiovascular issues to asthma flare-ups. 

Recent research has also linked wildfire smoke inhalation to certain mental health problems such as dementia, which my colleague Kristoffer Tigue covered in September. Indoor air quality issues are not limited to residential buildings; long-term care facilities, nursing homes and schools across the U.S. have suffered from poor indoor air quality levels during wildfire events, which can be particularly problematic because children and elderly individuals are among the most vulnerable to smoke-associated health risks. 

As climate change continues and fires worsen, a growing number of individuals could be exposed to wildfire smoke. One study found that from 2006 to 2020, there was a 27-fold increase in the number of people experiencing unhealthy air at least one day per year. Last June, wildfire smoke from Canada put around 100 million people across 16 states under air quality alerts in a single day. At that time, New York City briefly reported the worst air quality of any city in the world—I can attest firsthand that the smell of smoke burned my nostrils for days as I huddled next to an air purifier in my former tiny Manhattan apartment. 

Prior to this uptick in wildfires, the U.S. made strides in improving outdoor air quality by reducing pollutants associated with industrial activities under the Clean Air Act. However, “wildfire smoke is undoing a lot of that progress,” according to Elliott Gall, a mechanical and materials engineering professor at Portland State University who studies indoor air quality. 

How Do We Improve Indoor Air Quality? When a wildfire smoke event first hits, governments will often issue advisories like those currently in place across the Midwest to close windows and shut off ventilation systems. In the long-term, the ultimate key to cleaner indoor air is filtration, Allen said. 

“If you have high levels of filtration in your building, even if the outdoor levels are extremely dangerous, you can have safe levels indoors,” he said, adding that MERV 13 air filters or portable air cleaners with a HEPA filter are among the most effective for consumers. These can also help protect against other indoor air pollutants such as particles from viruses, cigarette smoke or ash from coal-fired power plants, he said. 

However, not everyone has equal access to these technologies. In low-income neighborhoods, older buildings are more likely to have cracks or poor sealing, leaving more entry points for wildfire smoke and other pollutants to seep inside. Many can’t afford quality air purifiers or ventilation systems and are facing dual threats from summer heat waves, with little to no access to air conditioning. 

“Housing quality plays a big role in this. If you’re in an older, leakier home, you’re going to be exposed to more wildfire smoke,” Gall said. 

But better indoor air quality doesn’t always need to be high tech or high cost. Inspired by the somewhat effective DIY cloth face masks people made during the early days of the COVID-19 pandemic, Gall and his research team created an air purifying system using a simple box fan and a long, cotton sock (the first sample was sewn by Gall’s mother-in-law). In February, the Environmental Protection Agency announced that Gall and his team’s prototype product, dubbed The Cocoon, won the second phase of the the Agency’s “Cleaner Indoor Air During Wildfires Challenge,” an initiative launched in 2021 to kickstart the advancement of inexpensive technologies to improve indoor air quality. 

“The original motivation was that someone could kind of MacGyver it together,” Gall said, adding that their goal is to eventually create a design that people can buy or make themselves. 

Other initiatives are happening at a government level. To help minimize the spread of Covid, the Biden administration has delivered hundreds of billions of dollars in federal funds for schools, public buildings and other settings to expand access to clean indoor air, which can also help mitigate the effects of wildfire smoke. Several states across the western U.S.—which are often the most vulnerable to wildfire smoke—received funding from the EPA to improve outreach and training programs in HVAC filtration maintenance to improve indoor air quality. 

In February, the EPA announced tougher standards on outdoor particulate air pollution in the U.S., decreasing limits from 12 micrograms per cubic meter of air to 9, which could consequently help limit indoor air pollution exposure. However, some experts question the effectiveness of this standard to address wildfires, which can spread smoke far beyond where they originate and can have a particularly disastrous impact on low-income communities that may not have a refuge inside. 

“The thing I’m trying to drive home is that outdoor air pollution is not just an outdoor problem,” Allen said. “All of this penetrates inside the places where we live and work and go to school. And so we have to start thinking of buildings as a key component of climate resiliency.” 

More Top Climate News

On Monday, the Federal Energy Regulatory Commission (FERC) approved a new rule that requires U.S. electric grid operators to plan 20 years in advance when planning transmission line expansion. 

The new rule will mandate operators to take into account the forecasted increase in frequency of extreme weather events and the growing number of states requiring more wind and solar projects, which have historically been stalled since there is not currently enough capacity to integrate all of them on the grid, reports The New York Times. It could take years for the rule to go into effect, and some Republicans have already voiced opposition to it, stating that the expansion of wind and solar could ramp up costs for consumers. 

Meanwhile, in California, an experiment testing a cloud-brightening technique that scientists think could help cool the atmosphere amid global warming was halted on May 4 over potential health concerns, reports the San Francisco Chronicle. According to a Facebook post from the City of Alameda, officials are “evaluating the chemical compounds in the spray to determine if they are a hazard either inhaled in aerosol form by humans and animals, or landing on the ground or in the bay.” This shutdown is the latest in a wave of backlash against geoengineering techniques to address climate change, which I wrote about in March. 

Also in California, lifeguards have spotted droves of sick and emaciated pelicans along the coast in recent weeks. Experts are not yet certain why these pelicans are starving because marine life is wildly available off the Pacific Coast at the moment. A similar animal mystery is playing out in Florida, where many endangered sawfish have been spotted spinning, whirling and in some cases, dying, an unsettling trend my colleague Amy Green is following from the Sunshine State.