Aerial mucosalivary droplet dispersal distributions with implications for disease mitigation

TL;DR

This study experimentally analyzes how mucosalivary droplets disperse and deposit on surfaces during human exhalations, revealing the effectiveness of masks in drastically reducing droplet spread and providing insights for disease mitigation.

Contribution

It provides detailed experimental data on droplet dispersal patterns and the impact of source height, along with quantifying mask efficacy in reducing droplet spread.

Findings

Most droplets deposit within 2 meters of the source.

Droplet deposition follows an exponential decay with distance.

Masks reduce droplet dispersal by at least a hundredfold.

Abstract

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.