LOS ANGELES (CBSLA) — As part of the pathway to reopening school buildings for in-person learning, Los Angeles Unified School District and others said they have upgraded their air filtration systems.

In Santa Clarita, the William S. Hart Union High School District said it has spent millions on COVID-19 safety measures to keep students and staff safe once they return to campuses.

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“We have purchased more than 1,200 portable HEPA air filtration units for classrooms and communal office areas,” Collyn Nielsen, chief administration officer, said. “Also, we’ve taken a look at our permanent HVAC systems in our buildings, and we’ve changed out the filters to MERV 13 filters as recommended by the county department of health.”

According to the Western Cooling Efficiency Center at the University of California, Davis, filtration systems can remove carbon dioxide and airborne respiratory droplets which could pass the virus through the air.

“I kind of have this analogy where I imagine there’s little glitter particles all over the air and how are we going to get them out of the air,” Theresa Pistochini, UC Davis engineering manager, said. “We can replace them or we can filter them.”

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Pistochini said there are two options for getting particles out of the air: ventilation or filtration.

“One is you could replace the indoor air with outdoor air, and that’s called ventilation,” she said. “And the other thing you can do is you can move the air through a filter and that will remove a certain fraction of particles.”

She said studies have shown that even in non-pandemic times, the better the ventilation in schools, the better the students and teachers perform.

“This has become very urgent because of the pandemic, but this is not just about the pandemic,” Pistochini said. “There are studies that show how important it is to have working ventilation systems, because they improve student attendance, they improve student performance.”

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Pistochini said cleaning and upgrading the built-in filtration system was key and that portable filters alone were not sufficient, though the do provide an added layer of security.