Do you have any sources on this? I'm keen to know more, but googling results in either very dry researchpapers or ads on either co2 meters or air purifiers.
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)