Why YSK: Back in 2020 when Australia had our massive wildfires I still had to drive to work everyday in the smoke. I also went and got my car serviced around the same time and they showed me how dark my cars air filters had gotten after just a few weeks of those conditions. The air filters in cars aren’t designed to filter out so many particles so as soon as you can you should get them replaced.
This is also very true for the air filters on your home furnace/heat pump, if you have one. Even if you aren’t running the heat, if you are running the furnace/heat pump’s fan to circulate air periodically (which you should be doing to avoid stagnation), air is still passing through the filter. I live in the Seattle area, and our furnace filter comes out absolutely filthy black after every bout of wildfire smoke. It nasty.
A fun fact about those furnace filters is that combined with your aver 20-22 inch box fan they’re a cheap way of getting very clean air in your house with a Corsi-Rosenthal box. https://cleanaircrew.org/box-fan-filters/