You're mis-reading my post. _Pittsburgh_'s air isn't great. The air inside my house is great, thanks to a lot of air filters.

The greater Pittsburgh region is #11 on the most polluted cities in the US by short-term particle pollution: https://www.lung.org/research/sota/city-rankings/most-pollut...

It's not Mumbai. But it's bad by US standards.

The thing that's not fully optimized are the CO2 levels in my house. As I've continued improving the air sealing in the house to reduce my heating and AC costs, it's something I want to address a little more in the future through active ventilation.