Surgical Masks Surprisingly Effective Against PM2.5

There’s a fantastic educational poster from Greenpeace that I’ve seen in several places (for example, here on AQIcn).

It offers great advice on masks that protect us from PM2.5, soot or wildfire smoke. But then it says this:


“No effect” it says. But when I read the cited articles, I saw no tests of surgical masks.

News outlets have made similar claims. In the US, National Public Radio claimed that surgical masks can “only block large droplets” and thus won’t capture coronavirus particles.

NPR Surgical Masks Coronavirus Capture

But I should be “nerd fair” and not strawman their idea. When Greenpeace says “no effect,” maybe they really mean “a small effect.” Then how small would be small? 10% of particles? 20%?

Size of coronavirus particle pm2.5 and bacteria

I’ve read three independent tests of surgical masks, and here’s what I learned: surgical masks are shockingly good at protecting against particulate pollution.

1. The Edinburgh Study

Researchers from Edinburgh University tested how much diesel exhaust different masks could block, including a surgical mask. They tested down to .007 microns. That’s way smaller than 2.5 microns, and it’s 10 times smaller than the coronavirus. The surgical mask blocked 80% of particles.

Surgical Mask Effectiveness Study Data PM2.5


2. Dr. Saint Cyr’s Fit Test

In Beijing, Dr. Richard Saint Cyr fit tested several masks on his face using a fancy fit-testing machine.

The surgical mask did a bit worse here – 60%. That’s likely because this is a fit test, and so it takes into account leakage around the mask.

Surgical Mask Fit Test Effectiveness PM2.5

This isn’t the only test. Surgical masks scored 50% in Smart Air’s fit test of masks in India and 47% in a test in Singapore. Still, 50% is far from “no effect.”

3. U Mass Study

In a study out of the University of Massachusetts, researchers tested N95 masks, cloth masks, and a surgical mask. They tested the masks on a mannequin to mimic effectiveness while a person is wearing it, not just the particle capture rate.

The left-most mask is a 3M N95 mask, the “N95 mask2″ is a Moldex N95, and the right-most mask is a cheap surgical mask bought from a street vendor in Kathmandu. The surgical mask blocked about 60% of .03 micron particles and over 90% of 1 micron and 2.5 micron particles.

Moldex N95 Mask Test Review Data

Bottom Line: Surgical Masks Surprisingly Effective Against PM2.5

Scientific fit tests and particle penetration tests find that surgical masks as cheap as 1 RMB (US$0.15) block between 60-90% of particles. That includes even really small particles and even while a person is actually wearing it.


Should You Wear A Surgical Mask?

Now let me be clear. I’m not recommending that everyone use surgical masks. I wear N95 and N99 masks because tests show they fit better and capture more particles. But if professional masks are unaffordable or it’s a bad air day and you forgot your normal mask at home, or even if you’re caught out with a wildfire, ducking into a pharmacy and spending 1RMB on a mask will significantly reduce your exposure to particulate pollution.

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