How to keep indoor air clean during wildfires

May 24, 2023

The worry was palpable this week: With D.C. under major air quality warnings due to massive wildfires in Canada, is it okay for kids to go to school? Should everyone be wearing masks?

My answer: Turn to HEPA-grade air purifiers, if you can. On Wednesday, they were still easy to get with one-day delivery, something I found both revealing and also a little worrying — though by Thursday it was harder to get some that quickly.

Then I set to the work of smoke-proofing my house as much as possible, hoping to squeeze as much protection as I could out of what we already had — windows, several HEPA purifiers that I could place wherever I liked and two at-home air quality monitors — not necessarily what scientists use in the lab, but better than nothing. At the end of the process, I came to this conclusion: Improving your indoor air quality is possible, but not always easy — or cheap. And accepting that you can make things better, but not perfect, is very important.

As a writer who covers climate change and the environment and also covered the coronavirus pandemic, I’ve had to learn more than most about air quality, how much it matters, and how to preserve it. This doesn't make me an expert, merely an occupational dabbler. Still, it seems clear to me that during an event like this, there are a number of things everybody should know:

HEPA air purifiers, which are capable of removing many types of small particles from the air that we might otherwise breathe — including pollutants, bacteria and viruses, and allergens — are becoming an ever larger part of our lives, necessarily so. In the context of the pandemic — or just flu season — they can reduce transmission of airborne respiratory viruses such as the coronavirus and the flu. During a poor air quality event they can protect your lungs, your bloodstream and even your brain — because we are still learning about just how dangerous small particles of air pollution can be.

"I look at them as the seat belt for lungs. Put them where you spend most of your time," said Mark Hernandez, an air quality expert at the University of Colorado at Boulder who is helping to install these filters in schools across the state in partnership with Colorado's Clean Air for Schools program.

Hernandez thinks HEPA filters are one of the simplest and best moves to protect against wildfire smoke — as long as they are certified by AHAM (the Association of Home Appliance Manufacturers), a stamp ensuring that the devices do what they say they do.

"It costs you 10 bucks a year to run them on electricity, 50 bucks a year for a filter; do the math, and it's pennies a day," Hernandez said. "And we know they work. This is now a 60-to-70-year-old technology; it came out of NASA. That's why they’re on the space shuttles, because they work."

How long will wildfire smoke last? Here's what we know.

In many cases, you can also attempt to clean the air at a central point in your home by putting strong filters within your HVAC system. Experts generally recommend MERV-13 level filters or higher. Even so, it doesn't hurt to have portable HEPA filters that can be placed in key locations, especially where people are spending time or sleeping. (Commercial buildings, schools and other larger structures frequented by many people will need additional steps to clean air — these are steps for your individual home.)

Taking steps such as buying a HEPA system can be expensive. It is possible to make your own filter for less out of a box fan and other common household items.

When I got home and started to secure my house, I found the air quality levels weren't terrible but weren't always great, either. Levels of PM2.5 — tiny, harmful air pollutants found in wildfire smoke — in my office, for instance, were well above my comfort zone, albeit still much lower than levels outside. Levels were even higher in the basement of the house.

I quickly found some potential culprits. Several windows in the house had sagged downward, leaving them slightly open — something that can just happen with windows if you don't latch them, which in many cases we hadn't. This took about five minutes to fix.

In my basement, the worst room in the house was the sole one that featured a window air-conditioning unit. I took it out and closed and latched the window. Measurements slowly began to get better.

The steps that I took, which anyone can take, will not only make the air indoors cleaner but also seal off my home, saving energy. (Longer term, one can do even more to seal your house, such as caulking around the outside of windows.)

Which is not to say it's easy or straightforward. We’re told to ventilate our houses when cooking, especially if we have gas stoves, and when we have a lot of people over. Then we get a wildfire smoke event, and suddenly the same houses need to be well-sealed. It's no wonder that people often find indoor air quality measures confusing.

The norms for how we measure air inside homes don't help. We have screens, typically in the form of thermostats, that tell us the indoor temperature and sometimes the humidity. But you generally have to go out and buy special products to learn about indoor carbon dioxide, particulate matter, formaldehyde and other measurements.

Here's how to protect yourself from wildfire smoke

"What I’m hoping for as an educator, is that we can reduce this to a dashboard," Hernandez said. During the pandemic, Hernandez outfitted a restaurant in Big Sur, Calif., with both sensors and multiple air purifiers so that he had knowledge of, and substantial control over, the indoor air quality levels — and whether respiratory particles could be transmitted.

"You get in your car, and you get used to the gauge that's reporting oil pressure should be in this range, the gauge reporting temperature of my engine should be in this range. You get what's normal and what's not. And that's really where we need to be," Hernandez added.

Experts today are simultaneously predicting future pandemics and worsening climate change. Meanwhile, we keep learning more and more about the dangers of breathing in small particles of air pollutants.

In this context, it seems pretty clear that air purifiers with HEPA filters and other measures are going to become increasingly common, like masks — which also, when of high quality and worn properly, help protect against wildfire smoke inhalation.

The massive blazes will still be episodic events, hard to predict very far in advance and temporary in how they afflict us. But high-quality filters simultaneously remove pollution from other sources, ranging from smokers to the byproducts of burning from a gas range. And if and when another airborne pandemic comes, they’ll probably help there too. Meanwhile, indoor air quality measurement devices can alert us to when something is abnormal.

So — measuring and filtering, measuring and filtering. While it takes work and some learning, and has a cost, the good news is that the tools are available to let us do this.

In my case, the steps above probably improved my indoor air quality and made my family safer during this extreme event. But the process was also pretty humbling. Right when I thought I’d thought of everything, I realized my own bedroom, which I had not tested, thinking it was like other rooms near it, still had relatively poor air quality. Presumably, outdoor air was still getting in somehow. As of this writing, I haven't entirely figured out why.

How bad is the wildfire smoke in your city? Use our tool to find out.

Perhaps the most important words of wisdom that I heard from Hernandez speak directly to this. "There's no such thing as safe; it's always safer," he told me. Safety is relative. We’re always breathing at least some air pollution. It would be better if we breathed zero, but that's not possible. At the same time, it's also possible to become overly stressed about particles that we can't control — which isn't healthy either.

So, yes, think about your home or living space, how it works, take some measurements, try to filter some air. That's the world we live in, and consciousness is a good thing. At the same time, though, recognize that all of humanity is going to take its dings from climate change and none of us are exempt. Remember that in the end, we’re all in it together and all just adapting as best we can.

Latest news: Smoke from Canadian wildfires spread over much of the Midwest, Ohio Valley, Northeast and Mid-Atlantic, bringing dangerous air pollution to the United States. Smoky conditions are expected through the end of the week. Follow updates on the wildfires and the impact on air quality.

Where wildfire smoke is the worst: Satellite images show smoke most densely covered the Northeast, but also extending into the Carolinas. Air quality in Philadelphia, D.C. and New York City was particularly poor, and officials urged at-risk residents to wear high-quality masks outdoors. See how bad the wildfire smoke and air quality are in your area.

Air quality and your health: Breathing in wildfire smoke is bad for your health. The EPA uses a color-coded system to measure air quality. Here's an explanation of what Code Red, Code Purple and more mean. Learn how to protect yourself including which air filters and air purifiers to choose for your home.

Environmental impact: Wildfires send greenhouse gases into the air, but Canada doesn't count some of them as part of its official emissions contributions, a Post report found.