Is it truly a conservative metric?
CO2 diffuses quite rapidly and should be more capable of permeating the structure than an aerosol/droplet. I would imagine microdroplets would behave much closer to PM2.5 particles? Also CO2 will pass right through a HEPA filter so you could have safe air with elevated CO2 in a sealed room…
Determining air changes per hour is not overly complex or expensive (blower tests for example) and should be able to provide some guidance for a structure. I like to think math can do a pretty good job of estimating room capacity based on ACH perhaps moreso than CO2 monitoring?
On a related note (more of a musing, and not directed as a reply to you):
Given the cost of these CO2 meters it wouldn’t be much more expensive to aquire some fans (turbulence helps settle particles out of the air) and large room hepa filters to actually improve safety…
