Ambient CO2 levels as a proxy for safe ventilation - COVID19https://www.fastcompany.com/90538531/this-is-the-safest-indoor-space-to-prevent-the-spread-of-covid-19-according-to-a-mechanical-engineer
"USING CO2 TO MEASURE AIR CIRCULATION
So how do you know if the room you’re in has enough air exchange? It’s actually a pretty hard number to calculate. But there’s an easy-to-measure proxy that can help. Every time you exhale, you release CO2 into the air. Since the coronavirus is most often spread by breathing, coughing, or talking, you can use CO2 levels to see if the room is filling up with potentially infectious exhalations. The CO2 level lets you estimate if enough fresh outside air is getting in."