A citizen scientist in the Boston area put together instructions so parents, teachers and others can build DIY air purifiers. Courtesy of Don Blair hide caption

This year, Hillary Creech – the parent of a 10th grader and wife to a teacher – had an unusual back-to-school shopping list.

She ordered a box fan, some high-quality air filters, and a lot of duct tape. Why? To make a homemade air purifier for the local high school where her husband teaches.

As an emergency room nurse practitioner, Creech has seen firsthand what the pandemic is doing, and, she says, she's been treating a lot of teenagers during the current COVID-19 surge. That has made her particularly nervous about high schoolers crowding into classrooms. And she is not alone.

Hillary Creech, of Jonesboro, Ark., built a DIY air purifier for her husband's classroom. "My husband's classroom in particular has a wall full of windows, none of which open," she said Courtesy of Hillary Creech hide caption

Hillary Creech, of Jonesboro, Ark., built a DIY air purifier for her husband's classroom. "My husband's classroom in particular has a wall full of windows, none of which open," she said

With the delta variant surging across the U.S., and the new school year is beginning, many people are looking to make the classroom environment as safe as possible. Experts say one key consideration should be indoor air quality. It's not a new issue – indeed, there have long been calls to improve school ventilation and filtration – but it's now an urgent issue. Like Creech, some teachers and parents are so concerned that they are turning to a homemade contraption called the Corsi-Rosenthal Box.

"It looks like a janky box that has four sides made out of these standard air filters. And the top of the box is a 20-inch box fan," said Don Blair, a citizen scientist in the Boston area.

Blair has been pulling together resources on a website and making step-by-step instructions to help parents and teachers build this box. The idea is simple: The fan sucks air through the filters, effectively cleaning it of particles the virus might be floating along on. Experts say filters with a so-called MERV 13 rating or better are ideal.

This DIY air purifier is designed by experts but can be built by an amateur in under an hour. Courtesy of Don Blair hide caption

"It probably takes about 10 or 20 minutes really to just assemble these things and tape them up. And if you do goof up then, no problem, it'll take you 30 minutes," Blair said.

The materials cost somewhere between $70 and $120, and the box should last an entire school year. The original idea for this DIY air purifier comes from Richard Corsi, the incoming dean of engineering at the University of California, Davis.

After Corsi threw the idea out on Twitter, Jim Rosenthal, the owner of Tex-Air Filters, built the first box. Corsi and Rosenthal agreed to share credit and hyphenated the box's name. Corsi says people have been testing the boxes and getting good results.

"People are now reporting 600 cubic feet per minute in clean air delivery rates. That's phenomenal. That's better than a lot of the more expensive HEPA-based portable air cleaners," Corsi said.

Don Blair, a citizen scientist in the Boston area, built a DIY air purifier. It's designed by experts but can be built by an amateur in under an hour. Gabrielle Emanuel/NPR hide caption

Don Blair, a citizen scientist in the Boston area, built a DIY air purifier. It's designed by experts but can be built by an amateur in under an hour.

Many schools have bought HEPA-based air purifiers or other well-studied technologies for improving air quality. But these solutions can be costly. And Corsi worries about the school districts that aren't doing anything or are turning to solutions that haven't been proven.

"We have almost no information about a lot of technologies that are being heavily marketed to school districts right now. They haven't been rigorously tested," he said.

One challenge is there is no national requirement for schools to keep their air clean and healthy – and there's no oversight. Last year, a study from the Government Accountability Office found that tens of thousands of schools across the country had heating, ventilation, and air conditioning systems that needed attention – and that was before considering COVID-19.

"The way we think about checking on the fire alarm system or the elevator, there's nothing like that for indoor air quality or ventilation," said Joseph Allen, an air quality expert at Harvard's T.H. Chan School of Public Health.

For years, researchers have been warning of the dangers of indoor air quality in schools. Studies have shown that students do better when there's better ventilation in schools: test scores go up, and fewer sick days.

Experts say a silver lining of the pandemic may be that it has increased awareness of indoor air quality issues in classrooms – and brought about new tools to address the problem.