Figure 5.

(a) Product of the sedimentation time of droplets τ_sed^sol (given by eq 13) and the initial droplet volume as a function of the initial radius R₀ for an initial height of z₀ = 2 m and an initial solute volume fraction of Φ₀ = 0.01. Results are shown for different relative humidities; in the case RH = 0.99, no evaporation takes place and the result (eq 1) is recovered (thick black line). The right scale shows the steady-state number of virions N_vir sedimenting in air assuming droplet production at a rate f_drop = 10³ s^–1 for a single droplet producer (m = 1) and for a saliva virion concentration c_vir = 10⁶ mL^–1 according to eq 14. (b) Same as part a but including the effect of air exchange with a rate f_air according to eq 17. Results are shown for RH = 0.5 and for four different air-exchange rates f_air in a closed room, assuming well-mixed air and a single droplet-producing speaking human, m = 1.