With the outbreak of the coronavirus in China in early 2020, millions of people have to become experts masks overnight. Yet masks are complicated. Which masks can protect me from viruses? Do surgical masks filter the coronavirus? Do I have to use an N95 mask to protect me from viruses like the coronavirus?
Fortunately, scientists have already accumulated hard data on air pollution masks that can answer these questions.
How Big Are Coronavirus Particles?
Scientists have already used electron microscopes to measure how big the corona virus is. Coronavirus virions (or ‘particles’) are spherical particles with diameters of approximately 125 nm (0.125 microns). The smallest particles are 0.06 microns, and the largest are 0.14 microns.
This means coronavirus particles are smaller than PM2.5 particles, but bigger than some dust particles and gases.
Now that we know how big coronavirus particles are, does a mask filter out these particles? Let’s break this down into two simpler questions.
1. Can air pollution masks capture coronavirus particles?
The skeptic case:
People might say: The coronavirus (and other viruses for that matter) is tiny – 500 times smaller than the diameter of a human hair. And masks are so thin. How could they possibly get those tiny coronavirus particles?
The scientific test:
Researchers from the University of Edinburgh tested different common masks by running a diesel generator (to mimic car exhaust) and piping the exhaust through different masks. They used a particle counter to see how many particles made it through the mask. Here’s my super scientific rendering of the setup:
One important detail: the particle counter they used measured particles as small as 0.007 microns. That’s over 10 times smaller than the coronavirus particle diameter. We’re talking about truly tiny particles here!
They tested a whole range of masks, and here’s what they found:
3M industrial filters were able to capture over 95% of particles down to 0.007 micron. That’s over 10 times smaller than the coronavirus. What might be surprising to some is that the surgical mask was able to capture 80% of the tiny particles.
Conclusion: Masks – including surgical mask and N95 mask – can capture tiny particles over 10 times smaller than the coronavirus.
2. “OK, they can capture particles even smaller than the coronavirus, but when you wear them, all the air just leaks in the side.”
The skeptic case:
Mask works in theory, but those tests aren’t on real faces! When you actually wear them, you can’t get a good enough fit, so they’re basically useless.
The scientific test:
To answer this question, you need a really expensive fit-test machine. Fortunately, we were able to get our hands on one machine to test a range of masks.
The blue tube is sampling air outside the mask, while the white tube is sampling air from inside it (more details on the mask fit-test methods ).
Smart Air co-founder Anna Guo and Beijing-based Dr. Richard Saint Cyr also did some tests, so I combined all of our data. Here’s how well the masks worked on our faces:
Several 3M masks were able to capture over 99% of tiny 0.01 micron particles (10 times smaller than the coronavirus), even while on people’s face. What’s more, surgical ones were surprisingly effective, capturing 63% of the tiny virus-sized particles.
Can Masks Protect Us from The Wuhan Coronavirus?
Bottom line: masks can filter out even the smallest particles – those 10 times smaller than viruses. What’s more, they work surprisingly well even while people are wearing them. Surgical ones are cheap and more readily available, and they do surprisingly well at filtering virus-sized particles.
Paddy graduated in aeronautical engineering from Bristol University, and now runs Smart Air’s operations from Beijing. He’s an advocate for open data, free information and transparent business.