Students have their temperatures checked while wearing masks during the first day of school on Wednesday, Aug. 4, 2021 at Freeman Elementary School in Flint. (Jake May | MLive.com)Jake May

Once the most fun part of the school day, lunchtime in the era of COVID-19 also became the most dangerous.

The combination of groups of students without masks speaking loudly in an enclosed public space is exactly what COVID-19 needed to spread.

It’s a scenario that University of Michigan aerosol chemist Andrew Ault specifically advised school districts to avoid during the heights of the pandemic.

As we continue to learn more about how COVID-19 and other diseases are spread in the classroom, leading researchers are now recommending three new (and non-politicized) ways to mitigate the spread on the local level.

The easiest way to measure the air filtration in a room is a simple CO2 monitor that can be purchased on Amazon for anywhere from $100 to $250.

Many of them have built in ratings systems for the CO2 levels in the room that it was used in, but typically, rooms that read having less than 1,000 parts per million have good to fair air exchange.

Anything above that and the likeliness of COVID-19 spreading in the room get much higher.

“If it’s up around 1,500 or something like that – every breath I take is two to four percent of something that just came out of somebody else’s mouth pretty much,” Ault said. “... If it’s 400 like I showed you in the beginning, it’d be like less than one percent (of someone else’s breath).”

For schools, the Associate Professor of Chemistry recommended having a staff member visit each classroom throughout the day to measure the CO2 levels of the room. Using that number, the staff member can then advise the teacher to open a window and bring in some fresh air.

“For example, my son goes to an older school that doesn’t have an HVAC system. They can’t put great, high-quality air filters into their air handling system because they do not have one,” Ault said. “But if this teacher opens the window, or better yet opens two to help get some airflow going, that’s going to make a big difference.”

In large public spaces, like cafeterias, bringing in fresh air can get a bit trickier.

COVID-19 aerosol transmission is comparable to cigarette smoke. Just because you are on the other side of the room, it can travel and build up in poorly renovated spaces.

In these cases, Ault and fellow Associate Professor of Chemistry Kerri Pratt recommended that schools do their best to divvy up students at lunchtime and even eat outside, when the weather permits.

The biggest thing to remember when trying to mitigate the spread of COVID-19 is air filtration – not wiping down surfaces or antibacterial sprays.

Researchers recommend that school districts, if they can afford to, host commercial HEPA air filtration units that both decrease aerosol levels and filter air immediately around students.

Many school districts began purchasing ionizers, ozone generators and other chemicals to remove virus particles from the air just to show that they were trying something to mitigate COVID-19.

In actuality, those might have made the situation worse by introducing harmful gases.

HEPA filters are one of the two best options for aerosol removal, with the second being the next recommendation.

A cheaper option to a commercial air filter – the do-it-yourself Corsi-Rosenthal cube can get the job done for less than $100 and a bit of elbow grease.

It’s a box fan with five MERV-13 furnace filters (available in packs for around $50) duct-taped together to form a cube.

One of these cubes, also commonly referred to as a Corsi-Rosenthal Box, was donated to the White House earlier this month in an outreach effort on the importance of clean air to prevent COVID-19 spread.

The low-cost option was discovered by Richard Corsi, Dean of the Engineering School at UC Davis, and Jim Rosenthal, owner of Tex-Air Filters, who built the first box.

It can last six months, effectively removing COVID-19 and other aerosols from the air. You just make a cube using the back of a box fan and five of the filters with duct tape.

Now, when using the DIY Corsi-Rosenthal cubes and CO2 level monitors, the CO2 level in a room will remain the same even with a Corsi-Rosenthal cube in it, but the COVID-19 aerosol particles themselves will be removed in part.

So, if school districts use multiple methods of mitigation, as recommended, do not fret if CO2 monitors come back with similar results after Corsi-Rosenthal cubes are engaged.

As with all COVID-19 mitigation techniques, school districts that employ multiple forms of mitigation have the most success against COVID-19 – and other airborne diseases like the common cold and influenza.

That includes wearing masks often and effectively, despite their politicization.

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