[clairity]

here's a USDA fact sheet summarizing the effects of CO₂ at different concentrations that's more easily digestible than an academic paper: https://www.fsis.usda.gov/sites/default/files/media_file/202...

[Rebelgecko]

There are a number of studies that have found that CO2 levels lower than the OSHA limit of 5,000 ppm can still cause issues like slight cognitive impairment and worse sleep (however there's also a few studies that have found no or minimal impact of levels below 5,000ppm)