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When There’s Smoke, Getting Indoors Isn’t Enough

Some interiors are quite protected from air pollution. Others aren’t.

Smoke in an apartment.
Heatmap Illustration/Getty Images

As the Northeast endures one of the worst wildfire days in recent history, the advice has been pretty simple: stay indoors, filter your air. And chances are, people who can follow this advice are getting it.

Marshall Burke, an economist at the Stanford Doerr School of Sustainability who has been remarkably helpful to this publication, has looked at past examples of severe smoke events and found there isn’t any big demographic gaps in who is seeking out information about what’s going on and how to respond. “On days like this, we actually see evidence that most folks are seeking out information,” Burke told me, “We can look at Google searches in English, we can look at Spanish, we can look in different zip codes. And we see pretty similar searches. Folks notice that things are bad, and they search for information.”

What people can do with that information is where the disparities start to show up.

There are essentially two levels of response to the kind of smoke New York is experiencing now or California has experienced in the past few years: whether you’re inside or outside, and what’s happening to the air inside your home or another building.

Burke’s research has shown that even indoor air quality can still be quite bad during a wildfire — something that is at least anecdotally confirmed today (I am writing this from my bedroom. My office and living room have older, leakier windows and have been abandoned to the smoke).

“Indoors, especially at the levels that New York City is seeing today, you'll see substantial infiltration of smoke into indoor environments. And so you need active mechanical filtration to get the rest of that smoke out,” Burke said.

Citing data from indoor air monitors sold by Purple, which then creates maps of air quality, Burke warned that “right now in New York, I was just looking, they're quite high,” referring to particulate concentration, “so I think that should make us pretty worried about how much of this stuff gets inside and for those who can to really double down on filtration.”

That’s typically achieved by buying air filters, which can run up to hundreds of dollars per device and may require multiple devices in a single home. There can also be runs on these devices during smoke events. My local hardware store, for example, was out of them and Amazon wasn’t delivering several recommended brands until Friday.

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  • When Burke and a team of researchers analyzed air quality data in the Bay Area in 2020, they found that concentrations of particulate matter inside homes were not related to how smokey it was outside. The homes they looked at "experienced nearly identical daily outdoor concentrations" on bad smoke days, but indoor pollution was "starkly different." Some homes saw concentrations of particulates more than five times the World Health Organization recommended limit while others were able to keep the concentration levels at one third the WHO limit.

    Burke and the researchers found that wealthier households “can more easily stay home, are more likely to seek information on protective technology, and are more likely to own indoor pollution monitors.” In short, the public health advice you’re hearing now from elected officials is more likely to be followed — and easier to follow — for the wealthy.

    Burke pointed to programs in California that provide air filters to low-income households as well as to ways people could construct their own filters. All you need is a fan and some MERV filters. “it works surprisingly well,” Burke said.

    He also pointed to the need to outfit schools and homeless shelters with filtration. “We're going to need to make those investments. Of course, we can't do that today. But this will happen again, and we could be more prepared.”


    Matthew Zeitlin

    Matthew is a correspondent at Heatmap. Previously he was an economics reporter at Grid, where he covered macroeconomics and energy, and a business reporter at BuzzFeed News, where he covered finance. He has written for The New York Times, the Guardian, Barron's, and New York Magazine. Read More

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