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Whether buying a model or creating your own DIY filter, there are ways to protect yourself.

When wildfire smoke started to drift into Nat Dean’s home in Santa Fe, New Mexico, she felt the way she had when a traumatic brain injury caused her breathing rate and, thus, blood oxygen levels to drop. She had to use an oxygen concentrator at home and carry a tank when she went out for years while her system recovered.

“After five years of carrying around oxygen, it’s like, I don’t want to have to do that again,” she says.

While breathing wildfire smoke, she started to feel again that she just couldn’t draw a deep enough breath and was quickly exhausted. When one of the air quality alerts on her phone mentioned a local nonprofit, the Forest Stewards Guild, was loaning out air purifiers, she decided to try it. With the free-standing air cleaner running, her fatigue eased. This spring, she bought her own and ran it through New Mexico’s record-setting wildfire season, which occasionally sends an orange haze and a smell like campfires into town. The New Mexico Environment Department has issued air quality alerts almost every day for 70 days, and staff estimate that about half of them have been for air officially deemed “unhealthy” or “hazardous” to breathe.

“We’re not getting the smoke plume all the time, but when we get it, it’s bad,” Dean says.

Smoke exposure can irritate the respiratory system, causing eyes to burn and noses to run, coughing, wheezing, difficulty breathing, headaches, nausea, even organ damage, and, possibly, cancer. The concern comes from airborne particulate matter, called PM 2.5 for its 2.5-micrometer size, which can penetrate lungs and enter the bloodstream. Exposure to PM 2.5 from wildfire smoke has been linked to doubling rates for respiratory hospitalizations, and the Centers for Disease Control and Prevention has even warned that wildfire smoke can exacerbate COVID-19. People living in the increasingly wildfire-prone American West, like Dean, are turning to portable air cleaners to create a “clean” room at home. These air cleaners are essentially fans with fine-grained filters that trap particulate matter.

“Wildfire smoke season has become more and more of a pressing public health threat where we have seasons that can last for months at a time now,” says Sarah Coefield, air quality specialist with the Missoula County Health Department. In 2017, a particularly rough wildfire season in Montana, “The smoke was so bad people could see it inside their homes, and if you can see it inside your home, the smoke is really bad—so now outside is hazardous and inside is hazardous, and what can you do to protect people’s health? Clean the air.”

Health organizations set safe exposure thresholds at lower levels for older adults and children, including teenagers; people with heart or lung disease, including asthma, as well as diabetes; and pregnant people. Keep an eye on smoke forecasts through the Weather Service, and check local air quality at AirNow to know when a solution needs to come into play.

There’s an alphabet soup of acronyms to consider when selecting an air cleaner. The clean air delivery rate, or CADR, estimates the volume of air that passes through the filter. It’s possible to run an air purifier designed for a smaller space in a larger room, but it won’t be as effective. For areas heavily affected by wildfire smoke, match the CADR with the room’s square footage.

“With a good air cleaner, as much as a 90 to 95 percent reduction — it can actually be really, really significant,” says Jeffrey Williams, an air pollution specialist with the California Air Resources Board. That’s provided the home is well-sealed and windows closed.

“The key thing is keeping the room closed,” says Srikanth Paladugu, bureau chief for environmental health with the New Mexico Department of Health. “You don’t want to let outside air in.” Which also means turning air conditioners to a recirculating mode, and shutting off evaporative coolers or other systems that draw air in. In Montana, Coefield says, where people often rely on opening windows at night to cool their homes and then close them in the morning, an air cleaner can purge a small room of most pollutants in about half an hour.

Keep an eye out for a filter rated for Maximum Efficiency Reporting Value (MERV) 13 or higher, which captures 90 percent of particles greater than 1 micron and 75 percent of those smaller than 1 micron. Check that the purifier is HEPA-certified. And make sure the device doesn’t produce ozone, another pollutant. The California Air Resources Board publishes a searchable list of products that produce less than 0.5ppm.

Those craving a DIY solution or only in need of a temporary fix can strap a furnace air filter to a box fan. The EPA recommends using a box fan made in or after 2012 for electrical safety upgrades. This set-up is nearly as effective and less expensive, but noisier. Whatever the approach, a filter that starts to look dirty or smell smoky needs replacing. Some central heating and air conditioning systems can take a MERV-13 filter, becoming a built-in air cleaner for the house. But some models risk overheating if forcing air through a filter that fine. Check the manual or with your HVAC servicer.

“We know that smoke is going to keep coming back,” Coefield says. “But there are really practical steps we can take to protect people in their homes. The technology exists—we don’t need to figure out how to do it, we know what steps we can take and that they’re effective.”