Has anyone created a cheap DIY gadget yet to test whether #HEPA filters need replacing?

I suspect that many of us are engaged in Air Purification Theatre, taking psychological comfort in filters that are well past needing replacing.

Or, alternatively, we're burning money by replacing filters prematurely. (Not a problem at a safety level, but a financial issue for those of us without money to burn.)

Do *you* use a valid scientific method to test your filters? If so, how do you do it?

Already own a QT3 Portable Air Purifier but need a new HEPA filter? 💨 We’ve got you covered.

QT3 HEPA Filters (2 pack) are on sale for $34.99 until May 23. Order yours today! ⏰

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공기청정기가 집중력을 높인다, 뇌과학이 증명한 12% 효과

https://habitdays.com/posts/11886

#AskFedi #IAQ #CleanIndoorAir #HVAC folks:
My apartment's HVAC system, which is connected to an individual rooftop unit with its own fresh air intake ducts--is currently down. My understanding is that the issue is with the control module that is connected all the in-apartment on this floor, so all of our units are turned off.
I have a CR box air purifier, and a small portable one with miniature #HEPA filters, and an #Aranet4 air quality monitor.

Maintenance have installed a one-hose portable AC unit, with thermal tape around the edges of the open window. From the perspective of minimizing aerosol concentration, what is the best approach with respect to fan speed/mode options, i.e., always on, or only when cooling; blocking the undercut in the door, and opening a window in a different room?

I had also considered not using the portable AC at all; minimizing opening of the door and venting via windows with colder air at night.