Surgical Masks Surprisingly Effective for 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, but then it says this:


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

But I should be nerd fair. Maybe they really mean “a small effect.” Then how small would be small? 10% of particles? 20%?

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. The surgical mask blocked 80% of particles.


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%. I suspect that’s because this is a fit test, and so it takes into account leakage around the mask. Still, 60% is far from “no effect.”

3. U Mass Study

In a brand new study out of the University of Massachusetts,researchers tested N95 masks, cloth masks, and a surgical mask on a mannequin.The surgical mask blocked about 60% of .03 micron particles and over 90% of 1 micron and 2.5 micron particles.

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.

Bottom Line

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

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 if it’s a bad air day and you forgot your mask at home, ducking into a pharmacy and spending 1RMB on a mask will significantly reduce your exposure to particulate pollution.

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