It's been, what, 30? 50? million years since atmospheric CO2 levels matched current outdoor levels, much less what happens inside.
the concentrations and types of particulate matter, however, is unprecedented, and as such, presents a higher inate risk, something that scientific research is really only starting to grapple with but so far is showing to be likely a serious risk to many (most?) species on earth.
with that said, i'm not trying to discourage your project in any way, just saying that for most people, addressing particulate (plus voc) risk is likely going to be the overwhelming majority of the benefits to be found in relation to indoor air quality. reducing co2 could be worthwhile if you have an especially airtight room/house, but nearly no houses are that airtight (passiv houses are meant to be so, however).