That's interesting about the cut to size carbon filter on your passive intake vents. I've been using them for years mostly to control light spill into a room (keep it darker in the actual room) and never had them give off particles.
I REALLY like
@olbobcat 's idea on the car filter. Could move my filter and fan outside and not have to use such a large extension on my Gorilla possibly. So thanks for that! Something to ponder for the future.
Olbobcat and I have the same humidifier. Absolute game changer for me. If you look on Amazon you can sometimes find them open box for around $70. I only need to fill it about once a week. If you're using RO or distilled water in your regular humidifier then maybe not so much an issue with particles. But the 4 gallon evaporative does seem to help (me) with heat.
Heat really starts to SUCK this time of year. Do you have AC, etc?