MINNEAPOLIS (WCCO) — As Minnesotans anxiously await Gov. Tim Walz’s announcement on schools in the fall, a new University of Minnesota study has analyzed how COVID-19 spreads indoors, especially in classrooms.

The experiment models airborne virus transmission through aerosols that are ejected when people speak. Researchers measured how those aerosols land on nearby surfaces or are inhaled by another person.

With the help of eight asymptomatic COVID-19 carriers, the researchers modeled how the virus traveled through the air in three indoor spaces: an elevator, a classroom, and a supermarket.

After running a 50-minute simulation in a classroom with an asymptomatic teacher consistently talking, the researchers found that only 10% of their aerosols were filtered out. The majority of the particles attached to the walls.

Credit: Suo Yang, University of MInnesota

“Because this is very strong ventilation, we thought it would ventilate out a lot of aerosols. But, 10% is a really small number,” said assistant professor Suo Yang. “The ventilation forms several circulation zones called vortexes, but the aerosols keep rotating in this vortex. When they collide with the wall, they attach to the wall. But because they are basically trapped in this vortex, and it’s very hard for them to reach the vent and actually go out.”

However, the researchers were able to measure virus “hot” spots, or places where the aerosols tended to gather. Their hope is to be able to avoid these common areas with the right combination of ventilation and interior design. For example, in the classroom, the virus aerosols spread less when the teacher stood directly under a vent.

“This is the first quantitative risk assessment of the spatial variation of risks in indoor environments,” said mechanical engineering associate professor Jiarong Hong.

The insight could inform how indoor spaces are arranged and disinfected. The researchers have recently collaborated with the Minnesota Orchestra to measure how aerosols travel while musicians perform at Orchestra Hall.

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