Aerial mucosalivary droplet dispersal distributions with implications for disease mitigation

We investigate mucosalivary dispersal and deposition on horizontal surfaces corresponding to human exhalations with physical experiments under still-air conditions. Synthetic fluorescence tagged sprays with size and speed distributions comparable to human sneezes are observed with high-speed imaging. We show that while some larger droplets follow parabolic trajectories, smaller droplets stay aloft for several seconds and settle slowly with speeds consistent with a buoyant cloud dynamics model. The net deposition distribution is observed to become correspondingly broader as the source height $H$ is increased, ranging from sitting at a table to standing upright. We find that the deposited mucosaliva decays exponentially in front of the source, after peaking at distance $x = 0.71$\,m when $H = 0.5$\,m, and $x = 0.56$\,m when $H=1.5$\,m, with standard deviations $\approx 0.5$\,m. Greater than 99\% of the mucosaliva is deposited within $x = 2$\,m, with faster landing times {\em further} from the source. We then demonstrate that a standard nose and mouth mask reduces the mucosaliva dispersed by a factor of at least a hundred compared to the peaks recorded when unmasked.