A: TL; DR: The Corsi Air Box (sometimes called the Corsi-Rosenthal Cube or a Comparetto Cube) is the hot new trend in DIY air purifiers! See links below for instructions.
With the return to in-person school for most US school children and many college students, we need to continue to use many layers of protection to reduce transmission of COVID-19. In addition to vaccination and masking, improved classroom ventilation is crucial. Many teachers are putting air purifiers in their classrooms. One CDC study showed that the use of HEPA filtration units reduced 65% of SARS-CoV-2 particle transmission. If your school district isn’t providing commercial purifiers, never fear, it’s not too hard to make an effective one yourself.
The homemade airbox can be easily assembled from:
1.) a 20” box fan
2.) 4 high quality MERV-13 air filters
3.) some cardboard, and
4.) a whole bunch of duct tape.
Follow the assembly directions in the image above or in the links below. The results for these homemade portable devices do better than some of the commercial HEPA air cleaners for a lot less money. Even so, the boxes cost around $100 to make.
Some guidelines for use:
• Do not touch or move the filters once the box has been used. Touching the filters can dislodge contaminated particles into the air. (Wear an N95 mask when disposing of the filters.)
• Filters should be replaced every 6 months. (Set your calendar reminders for March 2022 if you make them this month!)
• Place air boxes away from the wall (the center of the room is ideal). Similarly, don’t place two air boxes too close to each other or next to an open window (no need to filter the fresh air).
Aerosol Scientist Professor Linsey Marr recently tweeted about the measurement of carbon dioxide in her child’s classroom. Since carbon dioxide is released in exhaled breath, higher carbon dioxide levels indicate poorer ventilation. Dr. Marr shows that carbon dioxide increases during the course of the day in the classroom and decreases while the kids are out of the room for recess. In addition to using an air purifier, opening windows/doors, and getting students outdoors are all strategies that will help improve ventilation and air quality.
Instructions for a DIY Air Purifier:
Prior DP Post on HEPA Filtration Units and Ventilation