(This article was updated August 21, 2020.)
As wildfires continue to rage across Northern California, residents will probably have to deal with smoke and ash for weeks or even months. If that’s you, you may be concerned about the long-term health risks of breathing the smoke that remains, and looking for ways to protect yourself or your family.
While smoke contains carbon monoxide and particulate matter that can be hazardous to your health, the Environmental Protection Agency says “the long-term risks from short-term smoke exposures are quite low,” according to a guide to wildfire smoke for public health officials.
However, the E.P.A. also suggests that more vulnerable populations (children, older people, pregnant women and people with asthma or cardiovascular disease) may be more susceptible to the health hazards of wildfire smoke.
Of course, pollutants and the health hazards that come with them aren’t limited to areas exposed to wildfire smoke. We all breathe in harmful particulates.
“The air we breathe all the time has fairly significant pollution in it,” said Tim Heffernan, a science writer and editor at Wirecutter, a New York Times company.
Studies that definitively link air purifiers to long-term health benefits are rare, because long-term health is affected by multiple factors. (This is also why air purifiers may not be marketed as medical devices in the United States.)
However, Mr. Heffernan explained, “It is absolutely, unequivocally true that particulate pollution does impact health.”
To put it simply, they draw in polluted air, trap the particles, then blow out clean air.
In order to be HEPA certified, air filters have to remove 99.97 percent of particles that are exactly 0.3 microns in diameter — a size that’s especially difficult to filter mechanically. That is also close to the size of wildfire smoke particles, which are mostly in the 0.4 to 0.7 micron range, according to the E.P.A. HEPA filters remove much larger and much smaller particles, as well. Some of the models Wirecutter has tested were able to remove virtually all particles as small as 0.01 micron, one-thirtieth the HEPA standard.
Again, while the long-term effects of short-term smoke exposure may be low, any kind of particle pollution can still affect our health, and that pollution is more concentrated indoors — meaning nearly all of us can benefit from cleaner air.
“Most of us spend a lot of time indoors,” Mr. Heffernan said. “And indoor air is more polluted than outdoor air. It kind of comes down to what we have in our homes: pets, rugs, furniture that traps dust. And many homes are not terribly well ventilated.”
Especially if you’re older or have asthma or other respiratory conditions, you may want to consider an air purifier. All of the HEPA-certified models Mr. Heffernan tested with his colleague John Holecek were effective at removing particulate pollution.
For homes in smoke-prone areas, including those near wildfire-affected areas, Heffernan suggested running the purifier on high for an hour, then turning it down to medium or low, which should keep the amount of smoke in your home to a minimum.
How to choose an air purifier
When choosing an air purifier, it’s important to ensure first that the purifier is indeed HEPA certified; it’ll usually be listed as “true HEPA.” You’ll also want a model with a tight seal around the filter. “If it’s not well sealed, air is going to flow around the edges,” Mr. Heffernan said. “If it’s letting dirty air around the edges, you’re not getting the full effect.”
Some models may list a CADR (Clean Air Delivery Rate) rating. This measures the volume of air that will pass through the unit, telling you how efficiently the model will work depending on the size of the room. Mr. Heffernan suggested looking for a CADR rating of at least 200 or more for tobacco smoke (ratings are also given for dust and pollen). That means the unit effectively delivers the equivalent of 200 cubic feet of pure air per minute to a smoky room.
These models are often recommended for smaller rooms of about 300 square feet, and they will cycle the air four to five times per hour in a room that size, ensuring that pollutants are filtered quickly. This isn’t to say a model with a 200 CADR rating won’t work in a larger room, but it will work more slowly.
If you’re looking for a more cost-effective solution, you can also upgrade your existing HVAC (heating, ventilation, and air conditioning) system to improve air quality.
HVAC systems come with basic filters that trap larger particles, like pet hair. You can upgrade your filter to one that traps smaller particles, as noted by the filter’s MERV rating, or Minimum Efficiency Reporting Value. This metric indicates how efficiently the filter will reduce particulates that pass through it. (Some manufacturers use their own MERV-equivalent ratings. These are explained in Wirecutter’s guide to HVAC filters, written by Mr. Heffernan.)
The higher the number, the better the rating. According to the E.P.A., “Filters with a MERV between 7 and 13 are likely to be nearly as effective as true HEPA filters at controlling most airborne indoor particles.” There are also “whole house” purifiers that provide true HEPA filtration in HVAC systems, but these are expensive and may require upgrading your home’s air handler.
Wirecutter recommends MERV 12 or equivalent filters. However, Mr. Heffernan cautions, these can strain older HVAC systems by restricting the airflow as they become clogged with captured particles. Manufacturers typically recommend replacing filters every three months, Mr. Heffernan says, but when particulate pollution is high, as during wildfires, they can become clogged in less than half that time.
As effective as HEPA-certified air purifiers are, some come with dubious additional features. Many of them claim to produce ozone to destroy pathogens, which sounds impressive, but the California Air Resources Board warns against them. Ozone, or O3, is a respiratory system irritant that can cause health problems.
A 2008 ARB report said the “introduction of any amount of ozone into indoor spaces may result in increased levels of formaldehyde, ultrafine particles, and other pollutants.” In fact, if you are indeed in California, you may not even be able to order these types of units on Amazon.
Many purifiers claim to reduce VOCs, or volatile organic compounds, using an activated charcoal filter. “Very few of them actually do,” Mr. Heffernan added. “It comes down to the mass of the activated charcoal filter.” In order to be effective, the activated charcoal filter would have to be a minimum of five pounds to have any statistically significant effect, he said. Most contain a tiny fraction of that.
How to care for your air purifier
Maintenance of your air purifier should be minimal. Most HEPA filters are designed to run continuously for a year, though many manufacturers recommend checking them every six months. If there’s a fair amount of buildup on your filter, or you just want peace of mind, simply replace it.
Beyond purifying your air, there are additional precautions to take if you live in a smoke-adjacent area or you’re concerned about pollutants.
Many of these tips are common sense: Keep your windows closed, and avoid spending too much time outdoors to keep from bringing particulates into your home.
“I would also recommend simple tasks, like washing your sheets and pillowcases. You don’t want to spend eight to 10 hours on sheets filled with smoke,” Mr. Heffernan said. And if you’re planning to vacuum, remember that vacuuming can also kick up dust and smoke that has settled, so mopping may be a better approach.
Finally, if you’re using a paper face mask instead, or want one so you can go outside in a smoke-adjacent area, keep in mind that most of them have limited utility, as the E.P.A. points out in its guide. In order to offer adequate protection from smoke particles, you would need a mask that’s rated by the National Institute for Occupational Safety and Health as N95 or P100. These ratings indicate that the mask or respirator blocks out 95 to 99.9 percent of particles 0.3 microns or larger.
“So if you’re going to be outside and you want a mask, you need one of these certified masks,” Mr. Heffernan said. “A paper one won’t do any harm, but it shouldn’t give you a false sense of security.”