Masking for Smoke Isn’t Like Masking for COVID

The not-COVID reason to mask is here.

Late last night, New Yorkers were served a public-health recommendation with a huge helping of déjà vu: "If you are an older adult or have heart or breathing problems and need to be outside," city officials said in a statement, "wear a high-quality mask (e.g. N95 or KN95)."

It was, in one sense, very familiar advice—and also very much not. This time, the threat isn't viral, or infectious at all. Instead, masks are being urged as a precaution against the thick, choking plumes of smoke from Canada, where wildfires have been igniting for weeks. The latest swaths of the United States to come into the crosshairs are the Midwest, Ohio Valley, Northeast, and Mid-Atlantic.

The situation is, in a word, bad. Yesterday, New Haven, Connecticut, logged its worst air-quality reading on record; in parts of New York and Pennsylvania, some towns have been shrouded in pollutants at levels the Environmental Protection Agency deems "hazardous"—the most severe designation on its list. It is, to put it lightly, an absolutely terrible time to go outside. And for those who "have to go outdoors," says Linsey Marr, an environmental engineer at Virginia Tech, "I’d strongly recommend wearing a mask."

The masking advice might understandably spark some whiplash. For the majority of Americans, face coverings are still most saliently a COVID thing—a protective covering meant to be worn when engaging in risky gatherings indoors. Now, though, we’re having to flip the masking script: Right now, it's outdoor air that we most want to guard our airways against. In more ways than one, the best masking practices in this moment will require snubbing some of our basest COVID-fighting instincts.

The COVID masking mindset can, to be fair, still be helpful to game out the risks at play. Viral outbreaks and wildfires both introduce dangerous particles into the eyes and the airway; both can be blocked with the right barriers. The difference is the source: Pathogens travel primarily aboard people, making crowds and crummy indoor airflow some of the biggest risks; fires and their smoky, ashy by-products, meanwhile, can get stoked and moved about by the very outdoor winds we welcome during viral outbreaks. Conflagrations clog the air with all sorts of pollutants—among them, carbon monoxide, which can poison people by starving them of oxygen, and a class of chemicals called polycyclic aromatic hydrocarbons that's been linked to increased cancer risk. But the primary perils are the fine-particulate-matter components of soot, ash, and dust, fine enough to be borne over great distances until they reach an unsuspecting face.

Once breathed in, these particles, which the EPA tracks by a metric known as PM2.5, can deposit deep in the airway and possibly even infiltrate the blood. The flecks irritate the moist membranes that line the nose, mouth, lungs, and eyes; they spark bouts of inflammation, triggering itching and irritation. Chronic exposure to them has been linked to heart and lung issues, and the risks are especially high for individuals with chronic medical conditions—burdens that concentrate among people of color and the poor—as well as for older adults and children.

But N95s and many other high-quality masks have their roots in environmental health; they were designed specifically to filter out microscopic particulate matter that travels through the air. And they’re astoundingly good at their job. Jose-Luis Jimenez, an aerosol scientist at the University of Colorado at Boulder, recently put their performance to the test with an N95 strapped to his own face. Using an industry-standard test, he measured the particulate matter outside the mask, then checked how much made it through the device and into the space around his nose and mouth. Percentage-wise, he told me, "it removes 99.99 … I didn't measure how many nines; it was working so well." On broader scales, too, the protective math plays out: Well-fitting masks can curb smoke-related hospitalizations; studies back up their importance as a firefighting mainstay.

The key, Jimenez told me, is choosing the right mask and getting it flush against your face. Experts in the field even get professionally fit-tested to avoid contamination infiltrating through any gaps. Surgical masks, cloth masks, or any other loose accessories that aren't specifically designed to filter out tiny particles just won't do the trick, though they’re still better than not covering up at all. (If that sounds familiar, it should; viral or smoky, "masks don't care what the particle is," Marr told me. "They care about the size.")

N95 masks aren't perfect protectives either. They don't shield the eyes, and they aren't great at staving off carbon monoxide and the other gaseous pollutants that wildfires emit. (That's for a reason: Allowing gas through masks is how we continue to breathe while wearing them.) But gases are volatile and quickly dissipate; for Americans hundreds or even thousands of miles from the source of the smoke, "it's going to be the particulate matter that is most concerning to us," Marr told me. Even in the parts of New York and Pennsylvania where PM2.5 has rocketed up to dangerous levels, the carbon-monoxide stats have remained low.

Considering how dicey the discourse over masking has gotten, masking advice won't necessarily be embraced by all. Less than a month after the official end of the United States’ COVID public-health emergency, people are fatigued by face coverings and other mitigations. And we’re fast entering the stretch of the year when having synthetic polymer fabrics strapped across your face can get downright miserable, especially in the humidity of northeastern heat. But when it comes to avoiding the harms of wildfire smoke, experts generally consider masks a second-line defense. The first priority is trying to minimize any exposure at all—which, for now, means staying indoors with the doors and windows tightly shut, especially for people at highest risk. Paula Olsiewski, an environmental-health researcher at the Johns Hopkins Center for Health Security, also recommends running whatever air filters might be available; air conditioners, portable air cleaners, and DIY air filters all help.

It's also a good time, experts told me, to be mindful of the differences between filtration and ventilation, or increasing flow to turn over stale air. Both are crucial, sustainable interventions against respiratory viruses. But in the context of wildfires, excellent ventilation could actually increase harm, Jimenez told me, by allowing in excess smoke. For right now, stale indoor air—a classic COVID foe—is a smoke-avoider's ally. The masks come in for anyone who must go outside in a part of the country where the air quality is bad—say, above an index of 150 or so.

The move might feel especially counterintuitive for people who have long since stopped masking against COVID—or even ones who still do, simply because the rules don't mesh. Through the flip-flopping guidance of mask everywhere to mask until you’re vaccinated to actually, mask after you’re vaccinated too to mask only indoors, Americans never hit much of a stable rhythm with the practice. The inertia may be especially powerful on the East Coast, which has largely been spared from the scourge of wildfires that's constantly plaguing the West. (That puts the U.S. well behind other countries, especially in East Asia, where masking against viruses and pollutants indoors and out has long been commonplace; even in California, N95 and HEPA shortages aren't anything new.)

That said, our COVID-centric view on masking was always going to get a wake-up call. Wildfires—and viral outbreaks, for that matter—are expected to become more common going forward, even in regions that haven't historically experienced them. And for all their weariness with COVID, Americans now have far more awareness of and, in many cases, access to masks than they did just a few years ago. The wildfires aren't good news, but maybe a mask-friendly response to them can be. Smoke does, from a public-health perspective, have one thing going for it, Olsiewski told me: It is visible and ominous in ways that a microscopic virus is not. "People can see that their air is not clean," she told me. It’ll take more than ash and haze to break through the divisiveness around masks. But a threat this obvious might at least forge a tiny crack.

This story is part of the Atlantic Planet series supported by the HHMI Department of Science Education.