Surgical Masks Surprisingly Effective Against PM2.5

Surgical masks have a lot of bad rep for filtering PM2.5. There’s a fantastic educational poster from Greenpeace that I’ve seen in several places. Here it is:

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


“No effect” it says. But when I read the cited articles, I saw no tests of surgical masks on PM2.5.

News outlets have made similar claims. In the US, National Public Radio claimed that surgical masks can “only block large droplets” [1]. They say surgical or medical masks won’t capture tiny coronavirus particles. which measure 0.06 microns to 0.14 microns.

NPR Surgical Masks Coronavirus Capture

If I give Greenpeace the benefit of the doubt, maybe when they say surgical masks have “no effect” on PM2.5, 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 PM2.5, and here’s what I learned: surgical masks are shockingly good at protecting against particulate pollution, PM2.5 and viruses.

1. The Edinburgh Surgical Mask 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 PM2.5 (2.5 microns and below), 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 Surgical Mask 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% at filtering PM2.5. 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 on Surgical and N95 Masks

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.

Smart Air


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 there are situations when I might wear surgical masks. If N95 or N99 masks are unaffordable or unavailable; if it’s a bad air day and I forgot my normal mask at home; or even if I’m caught out in a wildfire. Ducking into a pharmacy and spending a few cents on a surgical or medical mask will significantly reduce your exposure to particulate pollution including viruses.

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