Are you confused over how a mask that stops particles and virion (which is what individual viruses are called) 3 microns big and bigger can be effective against Covid, which is .125 micron wide? Read on.
We were confused by this too, and then we came to understand a few things: First, while the individual Covid virion is in fact approximately .125 micron in diameter, the individual virion by itself is not what is being transmitted. It has to ride along on something else. It’s helpful to think of Covid19, with its spikes, as similar to those burrs that you end up having attached to your pants (or your dog) as you walk through the woods. The burr can’t travel on its own; it needs to attach to something else and go for a ride in order to spread the seeds within it. Similarly, the Covid virion needs to attach to something else, such as mucus, and that something else to which it is attached is much larger.
As explained in a surprisingly cogent and useful article in USA Today, “There is never a naked virus floating in the air or released by people.”
As this excerpt from the USA Today article explains:
“The virus attaches to water droplets or aerosols (i.e. really small droplets) that are generated by breathing, talking, coughing, etc. These consist of water, mucus protein and other biological material and are all larger than 1 micron.
The N95 filter is physically around the 0.3 micron size. But that doesn’t mean it can only stop particles larger than that. The masks are actually best for particles either larger or smaller than that 0.3 micron threshold. N95 masks actually have that name because they are 95% efficient at stopping particles in their least efficient particle size range — in this case those around 0.3 microns.
The reason that N95 masks work better on smaller particles is due to a number of factors, including two main factors:
The first is Brownian motion, which as you may recall from your high school physics class is the name given to a physical phenomenon in which particles move in an erratic, zig-zagging kind of motion. This motion greatly increases the chance they will be become ensnared by the mask fibers, much like a fly in a spider’s web.
Secondly, the N95 mask uses electrostatic absorption, meaning particles are drawn to the fiber and trapped, instead of just passing through.
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So while the COVID-19 virus itself is indeed smaller than the N95 filter size, the virus always travels attached to larger particles that are consistently snared by the filter. And even if the particles were smaller than the N95 filter size, the erratic motion of particles that size and the electrostatic attraction generated by the mask means they would be consistently caught as well.