The Cuboid: A DIY air purifier that's better than a box-fan (2021)
The Corsi-Rosenthal box[0] design using a standard box fan and furnace filters has been tested and verified to be very effective (and cheap):<p>[0] <a href="https://cleanaircrew.org/box-fan-filters/" rel="nofollow">https://cleanaircrew.org/box-fan-filters/</a>