Do ionizers really work?

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.


The Sqair air purifier Kickstarter

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I would love an answer or some insight on Noam’s question regarding the Molekule also!! I read the white papers on the product and it does sound awesome. But it’s expensive! Any insight on this product and their claims would be great!

Hey Eileen, it’s Paddy here in Beijing. Good news is: you’re in luck! Tom also wrote a Quora article about the Molekule purifier. Check it out here


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… Read more »

Noam, you’re in luck! Check out Tom’s article about the Molekule purifier here