(i) Constant load of 1000 virus particles per droplet
We consider
two droplets corresponding to the bimodal distribution with the
corresponding geometric mean sizes of 72 µm and 386 µm for the two
modes(3), with 1000 virus particles inside. The
droplets are ejected into quiescent air at 50 m/s (as commonly reported
for sneezing) at an average relative humidity of 65%, common in the UK
and an ambient temperature of 50°F (10°C). The time taken for the
droplets to evaporate to their ultimate size is
calculated(8), considering no internal resistance to
mass transfer and drying rate controlled by the external mass transfer
film. Water is considered as the evaporating material and assuming that
the presence of the virus does not hinder the drying of droplets. The
drying rate of the two droplets sizes is shown in Figure 1. The
evaporation time is 20 and 510 s for the two droplet sizes,
respectively, and the ultimate cluster sizes in both cases are around
1µm. Considering a smaller virus loading of 100 viruses, the ultimate
size will be obviously smaller and is around 0.46 µm.