The sibling comment is right, it doesn't help very much. The CO₂ level goes above 800 ppm (which is already considered unhealthy) in ~20 minutes, rises to ~2200

The sibling comment is right, it doesn't help very much. The CO₂ level goes above 800 ppm (which is already considered unhealthy) in ~20 minutes, rises to ~2200-2400 ppm (depends on wind speed and atmospheric pressure) in the course of a couple of hours, and then just stays there for days on end. I put all my pollution data into Grafana and it makes making decision when to open (or close) a window that much easier. (Yeah, you have to make a thought-out decision to not feel terrible. It's a whole ceremony.)