[DragonStrength]

I'd look at what the purifier claims to eliminate and find a quality monitor that will give you a reading. Most are portable, so you can compare to outdoor values directly. You're going to need some baseline to compare to though. If you have an AQI in the safe range already in your home, you'd have to contrive some actual experiments or find someone who already has.

I'll say I'm pretty distrustful of anything but filters personally. My mom purchased a purifier at one point which claimed to use UV light to purify but had no fan to actually pull air through the light, so obviously, it wasn't doing anything.