[Aurornis]

The paper is here: https://edworkingpapers.com/sites/default/files/Gilraine_Air...

I didn't see the model specified. They also said some schools got carbon filters, which is a different type of filter.

There's footnote saying many filters weren't even installed because some teachers thought they made the air "too dry", which is major placebo effect at work (air purifiers don't extract moisture from the air).

The entire paper is really not good quality, to be honest.

You can get a small HEPA purifier for a single room to remove particulates. The size of the filter, noise level, and amount of air moved are things to look for. Stepping up to activated carbon would remove VOCs, but cost significantly more (see IQAir, Austin Air, but ignore the cheap models that don't have 10-20lbs or more of activated carbon).