COâ‚‚ as an airborne-pathogen proxy: what the ratio actually tells you
COâ‚‚ does not measure pathogens. But COâ‚‚ and exhaled pathogen droplets share a source (occupants) and a sink (ventilation), so the indoor-to-outdoor COâ‚‚ ratio tracks the fraction of air in the room that other people have already breathed. This is why the Aranet model was widely adopted for ventilation monitoring during the pandemic.
Home Assistant
MQTT