However you clean the air purifier, whatever comes out is what isn't floating around the room anymore. That's a measure. And if the dirt is measurable it almost has to be helping. It's the measure I used judging the dust monkeys. They get black, rubbing on the rails. Whatever is on them is what was no longer on the rails.
And anecdotally, they aren't everything but make a
measurable improvement in longer term performance between serious cleaning, especially if I'm running trains a lot. Wash them and put them back on until filthy again.
