It is recommended that the content of CO2 should be below 1,000 ppm in an indoor environment. Some of the benefits with a low CO2 level are better concentration, well being, higher learning capability and improved patience recovery.
When the concentration reaches 1,500 ppm, we notice the poor air quality by being fatigue, having headaches and throat irritation.
Carbon dioxide is odourless and colourless in normal temperatures. It typically makes up around 360ppm (or 0.036%) of fresh, non-polluted outside air, but of course this level can rise in areas containing a lot of people or combustion processes.