Do ionizers really work?

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Are ionizers a scam?


The other day, someone on Quora asked whether ionizers actually purify the air. This is an important question because ionizer purifiers are all over the place. For example, I was at a friend’s apartment in the US, and I saw his tower fan had an ionizer button on it:



It’s also important because several friends in China have sent me links to products like this:



Amazing! A “miraculous purifier” that removes PM 2.5 and formaldehyde in just 30 seconds. And all that for far cheaper than regular purifiers and even cheaper than building your own purifier.

If this is true, my life in Beijing is now so much easier. But is it true?


So how do ionizers work?


Here’s my bedroom, with an ionizer and bad particles in the air:



That ionizer shoots out negative ions:



Those ions give particles a negative charge, which causes them to stick to surfaces, like my bed, the wall, and the floor:



That’s the principle behind ion generators. It’s hard to see it happening with these tiny particles, but you’ve seen it on a visible scale if you’ve seen someone rub a balloon on their hair and then stick it to a wall.



But wait #1

A summary of scientific tests of air purifiers found that most ionizers score “near the bottom of the effectiveness ratings” (p. 19). Their conclusion is that most ionizers are too weak to have an effect. Studies do show an effect if they use very strong ionizers–much stronger than most ionizers on the market (p. 19).


But wait #2

OK, so regular ionizers don’t work well, but we can use a big one! The problem is, when you put that many ions into the air, it produces ozone levels above healthy limitsOzone is harmful, so that’s not good!


But wait #3

Even if we use a really strong ionizer and even if we can accept the ozone, you might have noticed that the ionizer didn’t actually filter out the particles. It just made them stick to my bed, wall, and floor.

First, that’s gross. Since the particles floating around here in Beijing include things like arsenic cadmium, and lead, I’d rather not have them stick to my pillow.

Second, they’re still a danger. The particles are just sticking to my bed.



When I sit down on my bed, I’ll dislodge those particles, and they’ll float back into the air. Here’s my super scientific rendering of that process:



Ionizers go to court


Those problems are what led Consumer Reports to publish tests and warn people not to buy the Sharper Image Ionic Breeze. Sharper Image sued Consumer Reports; Consumer Reports won.



Bottom line: When people send me links asking about these “miraculous” purifiers, I tell them to steer clear. For a more effective method of cleaning indoor particulate pollution, use HEPA filters.



HEPAs can effectively capture indoor particualte matter like PM2.5. I’ve also done tests with my HEPA filter here.

Thomas Talhelm

Thomas is a new Assistant Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of Smart Air, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.

4 thoughts on “Do ionizers really work?

  1. Thant’s a very good summary on the ionizers subject. Thank Thomas!

    I was also interested in your opinion about this new “Molekule” air purifer:

    Specifically, I wanted your opinion about what the inventor of this purifier had to say about HEPA (and I quote):

    “HEPA (high-efficiency particulate absorber) filters remain the standard technology in existing air purifiers and, unfortunately, many harmful pollutants are too small for HEPA filters to trap. Larger pollutants like bacteria and mold may be collected by such filters, but they remain on the filter surface, multiply and are released back into the air. Because Molekule actually destroys even the smallest pollutants, they are permanently removed from the air you breathe.”

    1. He says that HEPA filters can’t absorb some pollutants that are too small. This is in direct contradiction to what I read about HEPA filters. I’ve read that HEPA filter’s efficiency is rated at 0.3 micron, because 0.3 micron is the most difficult size for HEPAs to filter out. Above or below 0.3 microns, HEPA filters are much more efficient (

    2. He claims that bacteria and mold multiply on HEPA filters, and eventually released back into the air. Do we have proof that this happens? Bacteria and mold fall within PM10, and we know that HEPA filters don’t release PM10 back (at least not more than they absorb), because we see that even a relatively old filter, can still clean a room (so if it does release something, it is way way less than what it absorbs).

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