What are ionizers and do they work?

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:


Ionizers 1


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


Ionizers 2


Amazing! A “miraculous air 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:


Ionizers 3


That ionizer shoots out negative ions:


Ionizers 4


Those ions cause the particles to stick to surfaces, like my bed, the wall, and the floor:


Ionizers 5


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.


Ionizers 6

But wait #1

A summary of scientific tests of air purifiers found that most ionizers have no noticeable effect on particulate levels (p. 8). 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, but we can use a big one! The problem is, when you put that many ions into the air, it produces ozone. Ozone 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. So let’s say Thomas comes home:


Ionizers 7


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 8


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.

So when people send me links asking about these “miraculous” ionizer purifiers, I tell them to steer clear.

Bottom Line: What Are Ionizers and Do They Work?

Ionizers shoot out negative ions which cause the particles to stick to surfaces.  They are not recommended because:
#1 Most ionizers are too weak to have an effect
#2 They produce harmful ozone
#3 Particles sticking to the bed, wall, and floor are still a danger.

One reason ionizers are unnecessary

In my mind, the biggest reason ionizers are unnecessary is that there’s already technology out there that is low-cost and highly effective. I use HEPA filters. HEPAs actually capture particles–be it PM2.5 or PM10–and they are backed by empirical tests (1, 2, 3, 4, 5, 6). You can see that effectiveness in action in this live test I did of a HEPA filter chewing through real Beijing air:


What’s more, HEPA filters don’t create other harmful pollutants like ozone. So I steer clear of ionizers. If your fan or HEPA purifier has an ionizer mode on it, I recommend keeping it switched off.


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Christina valdez

Please doctor Thomas, which one do you recommend?


There seems to be a difference between ionic air purifiers and ozone generators (https://en.wikipedia.org/wiki/Air_ioniser). Are you not exaggerating saying that all ionic air purifiers release ozone?
I have a panasonic nanoe-G Air purifying air conditioner in my apartment and as far as I can find information online, it does not release ozone, does it?


I read that HEPA filters cannot capture PM 2.5, is this right?

Definitely not, Chris! HEPA filters can capture over 99% of all particles above and below 0.2µm. That means PM2.5 is definitely included in the types of particles HEPA filters can capture. Check out this specific article on whether air purifiers can capture PM2.5


I am looking for a reasonably accurate and priced PM2.5 tester for use at a small school and my home. Under $200?? can you help. There are many out there.

Yes, you’re right! There are so many air pollution monitors on the market it makes it difficult to sort through them. We did some tests on three reasonably priced air pollution monitors, you could check out that review!

Ryan Lichtenwalter

I have had great experience with a from Taobao, which I validated against official measurements. I suppose the entire line uses the same detector and circuitry, so while individual experience may vary, it’s worth trying at roughly 140 CNY, 20 USD.


I only validated its PM2.5 measurement.

It’s the VSON Technologies WP6910.