Investigating COVID-19 transmission risk with dry ice in shopping malls

Throughout the COVID-19 pandemic, researchers of all disciplines have pivoted to study various aspects of the virus’s impact. This includes undergraduate university students who contributed to a study exploring how aerosols spread in spacious indoor and outdoor settings.

With their work, Poydenot et al. built on 50 years of research into the turbulent dispersion of aerosols. To simulate an infected person in the middle of a large indoor space, the team heated a dry ice block inside a shopping mall. Using dozens of sensors along the mall’s corridor, they tracked how the gas dispersed over 30 minutes.

“We expected that the gas cloud would spread equally in all directions, but it turns out that isn’t the case,” said author Florian Poydenot. “In all of the places we tested, there was a small natural flow along the corridor length.”

The cone-shaped spread was also found when the researchers measured the response of fog droplets in a wind tunnel. The results showed the concentration of aerosols decreases as the inverse-squared distance from the source. By extending the results to derive a quantitative, absolute risk of infection in outdoor or large indoor spaces, the team hopes this work can help reduce the spread of COVID-19.

“This work has practical applications for infection prevention policies,” Poydenot said. “Many health agencies around the world use different and arbitrary ‘safe distances’ for social distancing, and we show here how to ground these policies on a solid physical basis.”

Source: “Turbulent dispersion of breath by the wind,” by Florian Poydenot, Ismael Abdourahamane, Elsa Caplain, Samuel Der, Antoine Jallon, Inés Khoutami, Amir Loucif, Emil Marinov, and Bruno Andreotti, American Journal of Physics (2022). The article can be accessed at https://doi.org/10.1119/5.0064826 .