In a letter to Science Mag, the researchers warned that there is a big distinction between the much-vaunted droplets that are 100 μm (100 micrometers) and the microscopic particles that are usually
60-140 nanometers, or on average, 0.1 micrometers. While droplets are tiny, they are still visible and fall to the ground. The virions, which are at least 1,000 times smaller, are only visible through a scanning electron microscope.
...
In other words,
because the virions of the coronavirus are roughly 100 nanometers, 1/10,000 the width of a hair and 1/30 the size of surgical mask filtrations (about 3.0 microns or 3,000 nanometers), surgical masks do not help. Cotton masks are really pathetic. The hydraulic diameter of cotton is roughly 200 microns, 1,429 times the size of the larger aerosol.
As a friend of mine
noted on Twitter, "If you were driving down a tunnel in a truck, the aerosol being the pickup, the tunnel would be 1.83 MILES WIDE."
