Filtering out the fines and ultrafines – the stuff that HEPA filters capture – makes a biiiiiiig difference in air quality.

A smaller supplementary unit made out of PC fans and N95s can do that. A 120mm Noctua fan's flow and pressure fits well for about three 3M Aura masks in parallel.

It's unhinged how good the air quality is in a room with a device like this.