A Physics Modeling Study of COVID-19 Transport in Air

Abstract

Objectives: Health threat from COVID-19 airborne infection has become a public emergency of international concern. During the ongoing coronavirus pandemic, people have been advised by the Centers for Disease Control and Prevention to maintain social distancing of at least 2 m to limit the risk of exposure to the coronavirus. Experimental data, however, show that infected aerosols and droplets trapped inside a turbulent puff cloud can travel 7 to 8 m. We carry out a physics modeling study for COVID-19 transport in air. Methodology: We propose a nuclear physics analogy-based modeling of the complex gas cloud and its payload of pathogen-virions. We estimate the puff effective stopping range adapting the high-energy physics model that describes the slow down of α-particles (in matter) via interactions with the electron cloud. Analysis Findings: We show that the cloud stopping range is proportional to the diameter of the puff times its density. We use our puff model to determine the average density of the buoyant fluid in the turbulent cloud. A fit to the experimental data yields , where  and  are the average density of the puff and the air. We demonstrate that temperature variation could cause an O (≲ ±8%) effect in the puff stopping range for extreme ambient cold or warmth. We also demonstrate that aerosols and droplets can remain suspended for hours in the air. Therefore, once the puff slows down sufficiently, and its coherence is lost, the eventual spreading of the infected aerosols becomes dependent on the ambient air currents and turbulence.