Thread by @39Magilla

(1) A wide distribution of sputum aerosol droplets containing coronavirus leave the nose and mouth of the infected person, but they all shrink as they evaporate, concentrating the virus and making filter masks less effective against them.

(2) The infected person's filter mask catches a larger percentage of the initial particles and also limits their outward velocities.

The combined effect is estimated to be a 95% reduction in viral transmission.

(3) If the infected person doesn't wear a mask, the aerosol particles are projected further and they arrive with concentrated virus bound to much smaller aerosol droplets, making a susceptible person's mask less effective.

(4) If the infected person and the the susceptible target both wear masks, three factors reduce viral transmission:
- Only the smallest aerosol droplets escape the first mask.
- Droplets are projected with less velocity.
- The droplets that do get through have less virus.

(5) Est. Viral Transmission Probabilities:

Neither wears a Mask: 100%
Infected w/o Mask -> Target w/Mask: 70%
Infected w/Mask -> Target w/o Mask: 5%
Both wear Masks: 1.5%

Also, despite misinformation MASKS ARE ABSOLUTELY HARMLESS

Please, please, wear a mask.

(6) Related ideas: As-to-V ratio

Microscopic particles have extremely large surface-to-volume ratios leading to rapid evaporation:

1.0 cm: 0.75 square centimeters per cubic centimeter
1.0 mm: 7.5
1.0 micron: 7,500
0.1 microns: 75,000

Note: Particles assumed spherical

(7) Related ideas: Settling/Terminal Velocities

Despite ballistic trajectory nonsense propagated by the WHO and CDC, clustering, air currents and air drag dominate the movement of tiny particles, due to their extremely high surface-to-volume ratios.

(8) Remember:

You don't know your infected until after you're infectious.

Prevent transmission at the source, before it becomes too small to stop.