Do Air Purifiers Remove PM2.5?

When I was coughing through Beijing’s airpocalypse and thinking about buying an air purifier, I wanted to know something first–do air purifiers really remove PM2.5?

 

Beijing Airpocalypse Smog Haze PM2.5

 

I wondered because I saw lots of air purifier tests on pollen, but pollen is generally 10 microns or larger, whereas I was really concerned about the stuff below 2.5 microns.

 

particle sizes

 

So I went out and bought a laser particle counter. This one tests down to particles 0.5 microns and above.

 

laser particle counter that tests if purifiers remove PM2.5

 

Then I set up a simple DIY purifier in my bedroom in Beijing like this:

 

DIY purifier Smart Air

 

And here’s what happened to the 0.5 micron particles in my room after I turned it on:

 

the data shows purifiers remove 0.5 micron particles

 

I’ve found similar results with three other major purifiers I’ve tested. On average, they removed over 80–90% of 0.5 micron particles from my room air in overnight tests.

 

purifiers remove particles

 

What About Even Smaller Particles?

For the longest time, I thought the effect stopped there. When I read about HEPA filters (the filters in these machines), they always said they capture particles 0.3 microns and above. So I figured they just don’t get smaller particles.

 

HEPA definition

 

Well it turns out I was flat wrong. It’s actually easier for HEPA filters to capture particles smaller than 0.3 microns (thanks to Brownian Motion). As just one example, here’s a test from a dedicated nerd (like me) who has a particle counter that measures down to 0.01 microns. He tested seven major purifiers for 10 minutes.

 

testing if purifiers remove PM2.5

 

The different purifiers he tested removed about as much of these ultra-fine particles (light blue) as larger particles (dark blue).

 

different purifiers' cost-effectiveness

 

Bottom Line

HEPA purifiers remove PM2.5—even the smallest particles of PM2.5.

So breathe easy!

 

P.S. Big purifier companies often use this misconception about HEPA filters to sell you own their own “proprietary” filters, like in the popular Molekule purifier.

 

Molekule purifiers

 

Now that you’ve seen the data, you won’t fall for this trick!

 

HEPA filter meme

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