On the Front Range, where most people live in Colorado (~Denver + north and south 60 miles), the air quality can actually get pretty bad due to inversion, and this has been noted since pre-statehood. We also are lucky enough to get a lot of wild fire smoke from California, Canada, the PNW, as well as our own home sourced wildfires. Maybe 2 years ago it felt like the whole summer was smoky, and we had stretches where the AQI was 500+ here in Boulder.

https://denvergazette.com/outtherecolorado/news/the-brown-cl...