These particles are actually so fine they remain airborne due to ambient air turbulence. The trajectory of an initial 72 µm droplet is shown in Figure 3, considering gravity settling under quiescent air conditions. The droplet is ejected horizontally at 50 m/s at 1.6 m above the ground level into the stationary air. The terminal velocity of the particle after reaching a virus packing volume fraction of 0.6 is 8×10-5 m/s and at 20 s the dry particle is 0.38 m above the ground, having a diameter of 1.36 µm. It reaches the ground asymptotically with time, and will require further 1.3 hours before settling onto the ground. In contrast, a droplet with an initial size of 386 µm (corresponding to the larger mode of the droplet size distribution shown in Figure 2) settles onto the ground after 1.2 s of ejection from 1.6 m height and under the same conditions as above, and travels a horizontal distance of about 2.3 m. The diameter of the droplet when reaching the ground is 384.3 µm, i.e. very little drying takes place for droplets of this size before settling.