What is an optimal CO2 concentration (a range of values or percentages) for maintaining baseline performance among humans? For example, short term exposure to CO2 concentrations less than 5% has negligible impacts on performance (I don't think this is true, it's just an example). If anyone happens to know any peer reviewed scientific literature regarding this topic it would be much appreciated. As an aside, my high school often has trouble maintaining tolerable concentrations (concentrations which have a negligible impact on performance) of CO2. I would like to attempt to find ways to perhaps maintain tolerable CO2 concentrations through improved ventilation, introduction of plants to classrooms, etc. Any help is greatly appreciated. Thanks!