I assume it varies significantly based on how many people per square foot are in a room. Humans exhale about 45,000ppm CO2. My somewhat educated guess is 6 air changes per hour would get many public settings close to that, and would be pretty easy to achieve. I base the 6 ACH on a prior study that 6 ACH reduced transmission by 82%, and I base it being achievable based on my own calculations at home with HEPA purifiers.
Like you’re probably never going to get a small concert venue packed with people to the target numbers, but societally that’s fine - if a ton of settings keep the R0 < 1, then overall spread would be pretty low still even if you have super spreaders in concerts and sporting events and so forth. And those who wish could always mask up in those settings. Keep in mind that stomping it out elsewhere also reduces the number of people that walk into a crowded indoor venue carrying COVID in the first place.
Society clearly doesn’t care about getting rid of covid, but minimizing the burden is going to prove to be economically beneficial and could probably be done cost-efficiently by implementing stricter ventilation requirements in public settings and trying to get stuff like office spaces, retail spaces, etc to the required numbers.
In my head, I’m thinking of restaurants as kind of the dividing line. Some of them could definitely hit the number at least some of the year (picture places that have huge windows or sliding floor to ceiling glass dividers between indoor/outdoor) and many others could never. Anything more crowded/indoor than a restaurant is probably never gonna make it, anything less crowded/indoor than restaurants probably could.
If I were POTUS I’d commission a study to see what the cost would be to implement an ACH requirement and HEPA requirement on public settings, as well as the savings from preventing the transmission of covid, cold, flu, etc. I’d then propose a tax credit for implementing and maintaining it, subject to quarterly inspection or something along those lines. Compliant public places would get a certificate they could place at each entrance to show that they’re in the program.
Requiring this in all public schools and federal offices would be a step 1 no brainer. Requiring it in K-12 private schools, doctors offices, hospitals, and pharmacies seems obvious too.
Obviously in a utopia my plan wouldn’t involve a tax credit for the wealthy. But in the real world, the best way to get it done is to get Republicans on board via tax cuts.