I can’t believe that I didn’t find out about Corsi Rosenthal boxes and other homemade air purifiers until a few months ago.
A Corsi Rosenthal box is a cube consisting of a box fan on one side, a cardboard square on one side, and furnace air filters on the other four sides. The fan draws in air through the filters. Because the smoke, dust, and viruses are stopped by the filters, the fan blows out MUCH cleaner air. There’s a Wikipedia entry on the Corsi Rosenthal box at Corsi–Rosenthal Box - Wikipedia .
I built a mini Corsi Rosenthal box based on a smaller 9-inch box fan and smaller furnace filters. An example is at https://www.texairfilters.com/a-mini-corsi-rosenthal-box-air-cleaner/ .
I also built an air purifier that consists of a bathroom fan with a shop vac filter attached to the exhaust. The fan sits on a wooden platform (for stability) and is housed inside a bucket with holes that I drilled into it. It’s loud, but that allows it to double as a white noise generator. I run this air purifier in my bedroom when I sleep. The white noise blocks out the sounds of firecrackers, sirens, and other noises.
There should be a Corsi Rosenthal box or other air purifier in every home, classroom, gym, church, office, etc. These homemade air purifiers offer so much more bang for the buck than commercial air purifiers and are also MUCH cheaper and less intrusive than the expensive renovations often required to improve the ventilation in buildings.