At last night's FIG meeting the topic of portable shop air filters came up. Check out the Corsi-Rosenthal Box - using MERV13 filters (capture 0.3 - 1.0 micron particles). Not quite HEPA levels but might get closer with higher MERV rated filters if the air resistance doesn't increase too much.

https://encycla.com/Corsi-Rosenthal_Cube

https://www.texairfilters.com/iaq-research-practice-in-action-the-corsi-rosenthal-box-air-cleaner/

https://www.texairfilters.com/a-variation-on-the-box-fan-with-merv-13-filter-air-cleaner/