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Does the COVID-19 air purifier work? How about smoke fires?


Ry Crist / CNET

COVID-19 continues to worry people around the world – and especially in the United States, where the death toll is approaching 200,000. At the same time, forest fires are destroying the west coast of the United States, displacing hundreds of thousands. As we adapt to new realities, new questions constantly arise. What types of masks should we wear? Is it safe to breathe the air in the Bay Area? Can air purifiers be a solution to any of these problems?

To answer the last question, we spoke to a number of air quality experts. We asked if air purifiers can solve ̵

1; or at least mitigate – some of our air quality problems, whether we talk coronavirus virions floating in aerosol droplets around our house, or wildfires and smoke.

After test a dozen of the leading air purifiers on the market, talk to specialists and read dozens of studies on the subject, we came up with some answers.

If I want an air purifier, how do I find the right one?

For those of you who already want an air purifier and want basic recommendations, I have already written a comprehensive article on this very issue. There are plenty of air purifiers on the market, and some of them are really impressive considering their reasonable price tags.

Continue reading for those who are still on the fence.

Do air purifiers really work?

This is one of the most popular questions online, and it is also a reminder of why close reading and skepticism are such useful tools when researching products as a consumer. Air purifier developers are not allowed to advertise their devices as health products in the United States for any reason – mostly because their benefits are not simple. Instead of claiming incredible health effects, purification ads usually focus on the number of harmful substances in the air and the effectiveness with which the devices filter them out.


Molekule, which sells some of the most aesthetically pleasing reindeer on the market, was recently forced by the National Advertising Review Board to retract a lot of misleading claims they have made since 2017.

David Priest / CNET

To answer the question in the most basic terms: yes, air purifiers generally filter particles efficiently out of the air – especially if they use a HEPA filter (more on them in the next section). But most of us already have a mechanism for filtering air effectively: the respiratory system. As a microbiologist and Vice President of Scientific Communication at the American Council on Science and Health, Dr. Alex Berezow recently pointed out in a blog post: “Living in the small air sacs in your lungs (called alveoli) are immune cells called macrophages. These ‘big eaters’ devour bacteria, viruses, fungi and all the other debris that happens to find their way into the lungs. “

In short, air purifiers work, but if you do not live in a particularly polluted environment or if you or your children are immunocompromised, you probably do not need one.

Do they protect against COVID, smoke from smoke or other seasonal pollutants?

HEPA, which stands for Highly Efficient Particulate Air, is the standard that describes most air purification filters currently sold in the United States. To meet the standard, a filter must remove 99.97% of the particles in the air that are 0.3 micrometers (a particularly difficult size to filter). HEPA filters are usually more efficient with particles that are larger and smaller than that size. Pollen, smoke particles and aerosol droplets that can transmit COVID can all be filtered out of the air with such a filter.

A colleague’s mother recently started using, for example, Coway’s air purifier and immediately noticed the improved air quality in her home in San Francisco. Also, one of our editors tested the Dyson TP04 air purifier under the recently dusty Sahara cloud saw the air purifier do his job admirably: “Gradually, the app’s line graphs for each type of pollutant began to fall. After an hour or two, everything was back in green territory.”

But the story is a little more complicated when it comes to COVID. Simply put, do not count on air purifiers to protect you from virus particles if you are cohabiting with an infectious person. When I talked on the phone with Dr. Richard Shaughnessy, director of Indoor Air Research University in Tulsa, said that the transmission of COVID usually occurs due to close contact with an infected person. If you sit on a couch and chat with someone who is infected, an air purifier across the room will not remove all the harmful particles they exhale before they have a chance to reach you.

An additional problem is the difference between capturing and killing virus particles. While HEPA filters will capture the particles, other technologies, such as UV technology, will kill virions. Unfortunately, such technology often comes with own risks.


Coway’s air purifier is one of the best on the market. It includes ion filtration technology, but has been certified by the California EPA which emits negligible or no ozone over time.

David Priest / CNET

I’ve heard of ozone from air purifiers. Should I be worried?

Ozone is a type of pollutant that a narrow set of air purifiers has been shown to emit in the past. Before we dive into that, it is good to understand the basic types of air purifiers on the market now.

The three most popular filtration methods that air purifiers use to clean the air are these: HEPA units remove particles by venting through a specially designed and standardized filter; activated carbon filter removes odor and gaseous pollutants by driving air over “sorbent media” that traps it; and finally produces ionic purer ions that adhere to particles.

Ionic cleaners work in a couple of ways. Some simply allow ionized particles to adhere to surfaces around the house (thereby “removing” them from the air). Others have a plate that collects the ionized particles and needs to be cleaned regularly. The latter are the units that have previously had problems producing ozone. Fortunately, standards have risen in recent years and third-party companies are now testing ionic air purifiers to ensure that they do not emit significant ozone into the home.

In general, I would avoid ionic air purifiers simply because they are not the most effective for the price. If you really want one, make sure it’s certified by Underwriters Laboratories or the California EPA and states that it does not emit ozone.

Who would definitely benefit from an air purifier?

The research here is a bit complicated. Without getting too far into the weeds, one of the clearest demographics that benefits from HEPA filters is air purifying children with asthma. Dr. Elizabeth Matsui, professor of public health and pediatrics at the University of Austin’s Dell Medical School, has researched the use of air purifiers in the homes of asthmatic children and talked about the value of air purifiers in such households.


Even an excellent air purifier like Blueairs 411 does not do as much as cleaning and ventilating your home.

David Priest / CNET

Air purifiers, she warned, are not a substitute for what she calls “proximal source interventions.” For example, a HEPA air purifier can reduce particles in the home of a smoker and a child with asthma by 25-50%. But this is not the best solution: preferably the person would stop smoking completely in the house. A clean and well-ventilated environment – and of course proper medical care – is much more important than an expensive air purifier.

And to be clear, while air purifiers can help relieve asthma symptoms in children, says Dr. Matsui, “There is no good evidence that we can currently change the environment in a way that reduces prices of asthma, whether it is with air purifier or in some other way. In other words, air purifiers are useful devices for children suffering from asthma, but they will not reduce the risk of a child developing asthma in the first place.


With so many air purifiers on the market, it can be overwhelming to find the right one.

David Priest / CNET

If you have any other questions that I have not answered above, be sure to ask them in the comments, and I will be happy to update the article with answers.

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