Airborne dispersion of droplets during coughing: a physical model of viral transmission

TL;DR

This study models droplet dispersion during coughing using realistic airflow simulations to assess SARS-CoV-2 transmission risk, highlighting the importance of mask use, social distancing, and the effects of evaporation and body presence on droplet spread.

Contribution

It provides a detailed physical model of droplet dispersion during coughing, emphasizing the size range with highest transmission potential and the impact of environmental factors.

Findings

Droplets 32-40 μm pose highest transmission risk.

Social distancing reduces transmission across all droplet sizes.

Droplet evaporation decreases counts but airborne transmission remains possible.

Abstract

The Covid-19 pandemic has focused attention on airborne transmission of viruses. Using realistic air flow simulation, we model droplet dispersion from coughing and study the transmission risk related to SARS-CoV-2. Although most airborne droplets are 8-16 $\mu$m in diameter, the droplets with the highest transmission potential are, in fact, 32-40 $\mu$m. Use of face masks is therefore recommended for both personal and social protection. We found social distancing effective at reducing transmission potential across all droplet sizes. However, the presence of a human body 1 m away modifies the aerodynamics so that downstream droplet dispersion is enhanced, which has implications on safe distancing in queues. Based on median viral load, we found that an average of 0.55 viral copies is inhaled at 1 m distance per cough. Droplet evaporation results in significant reduction in droplet counts, but airborne transmission remains possible even under low humidity conditions.