[legulere]

The soot they filter out of the air is very visible when you change the filters (they turn from shining white to grey). Air pollution is one of the world’s leading risk factors for death https://ourworldindata.org/air-pollution#air-pollution-is-on... . Though that varies a lot from country to country, it is a problem you can strongly reduce with throwing a tiny bit of money on it.

[gruez]

If the filter is only turning Greg it sounds like what you're seeing is dust rather than soot. I have a pm2.5 meter and over the winter/spring the reading is almost always 0 or low single digits, and my filters still turn grey