Two men with masks looking at a trombone player.

The air we breathe

CSE aerosol studies inform businesses and schools as they reopened

Restaurant booths divided by Plexiglass, masked trips to the grocery store, socially distanced students in sanitized classrooms—these images have grown more and more familiar as society struggles to cope with the coronavirus pandemic.

Yet, the question remains: how dangerous are these indoor activities? CSE faculty members Jiarong Hong and Suo Yang aim to find out.

Since the pandemic began, the pair have been analyzing how the coronavirus can spread indoors, from classroom settings to the Minnesota Orchestra Hall. Their findings have provided insight for businesses and schools as they reopened this fall and helped the Minnesota Orchestra devise a plan to maximize the safety of their musicians onstage.

“You have heard a lot about regulations of social distancing in different places, but they’re all talking about six feet,” said Hong, an associate professor in the Department of Mechanical Engineering.

“There’s been no quantification of how this rule should be adjusted under different indoor environments," he said. "Social distancing of six feet might not apply because it depends on how the aerosol particles accumulate and are transported in that space.”

Scientists largely agree that the main culprits of COVID-19 transmission are aerosols, which are ejected from our mouths when we exhale or speak. When an infected person does this, the SARS CoV-2 virus can hitch a ride on those aerosols as they land on nearby surfaces or are inhaled by another person.

In the CSE researchers’ first study, Hong and his team of graduate students measured the concentration of aerosols generated by people breathing and speaking. Then, Yang used that data to produce simulations of how those aerosols would travel throughout different indoor spaces—an elevator, classroom, and supermarket. They found that the strength and placement of vents plays a key role in how the particles disperse and deposit on the floor and walls.

“We learned that ventilation matters a lot,” said Yang, the Richard and Barbara Nelson Assistant Professor in the Department of Mechanical Engineering. “You need to do proper ventilation, otherwise it can make things worse. The location, the distribution of the vents all matters.”

Shortly after they began this work, the researchers were connected with the Minnesota Orchestra through Medical School colleague John Hallberg. The orchestra wanted to know how dangerous it would be to play instruments as a group onstage, and what they could do to mitigate this risk.

A laptop screen with a graph.
A University of Minnesota research team studied how aerosol concentration in a musical instrument varies based on articulation and slurring patterns, intensity of play, and use of special techniques. Photo by Travis Anderson.

Hong and his team got to work. They organized on-campus experiments to measure the aerosol concentration produced by 15 musical instruments, and eventually conducted tests in Orchestra Hall to visualize where the aerosols traveled after they exited the instruments.

The researchers also found that bell barriers (the technical term for instrument masks) and portable air purifiers could further mitigate the spread of particles.

Their findings were crucial in helping the orchestra develop its plan for fall, which involves COVID testing, light quarantining, musicians wearing masks, physical distance between the musicians, and the potential use of bell barriers and air purifiers onstage.

Now, Yang’s lab is working to create simulations based off Hong’s initial measurements of aerosol concentration from instruments. His goal is to show how the aerosols would travel throughout the auditorium, and where audience members would be more at risk if the orchestra held a socially distanced performance.

“I think that indoor air quality overall is a very important issue, but it’s been heavily ignored in the past,” Hong said.

“That’s why this research is important, so that people understand the importance of ventilation," he added. "It’s not just COVID, but in the future, other infectious airborne diseases could also be associated with indoor air quality.”

By Olivia Hultgren

Read more stories from our Winter 2021 college magazine at cse.umn.edu/InventingTomorrow.


If you’d like to support research in the University of Minnesota College of Science and Engineering, visit our CSE Giving website.