Comment by Llamamoe

The machine's pre-filters (https://www.amazon.ca/AlorAir-MERV-10-Replacement-CleanShiel...) basically are that "extra sacrificial initial filter." I'm not sure what a "pre-pre-filter" would look like that would make it any different than one of these.

Were you maybe thinking some kind of wire mesh, like the "washable pre-filters" in air purifiers tend to be? I did initially consider this; but, after running the air scrubber for a few months and seeing what actually builds up in the pre-filter, it seems like the pre-filters don't actually end up being coated in anything (dust/hair/etc) that can actually be rubbed/scratched away or even vacuumed out of them. Rather, just end up gradually blackening (due, I think, to fine [PM2.5] particulate making it partway through them before gradually embedding deep inside them); and gradually feeling more and more "skudgy" to the touch (due perhaps to some of those particulates being hygroscopic, and due to also trapping things like pollen/mold spores.) You can actually touch the surface of the fouled pre-filter and your fingertip will come away clean (but touching it won't be a nice sensory experience.)

I think, for helping with that kind of particulate, a wire mesh wouldn't do much if anything. The only "passive" thing that would help is a non-woven cross-linked fiber material, porous enough to not overwork the air scrubber's fan to the point of making it work harder / be louder / burn out sooner, yet layered and "internally labyrinthine" enough to capture particulate despite that porosity. I.e. the same material used in the pre-filter.

(If I could add an active component, I might introduce an intake-side ionizing air purifier, where particulate gets charged and then preferentially deposits onto the fins of a washable heatsink-like grille. AFAIK, those don't normally work at the sort of CFM being pushed by the air scrubber. But if anyone wants to design a better mousetrap here, that might be a direction to look into.)