CO2 application displays current concentration of carbon dioxide (CO2) in indoor air, and you can see in graphical format history of the concentration, so you can judge functionality of ventilation system , set up your ventilation system or you can ventilate according to. Carbon dioxide (CO2) is colorless, odorless gas. It is produced during metabolic activity of living organisms and during combustion processes. CO2 is useful for appraisal of indoor air quality. Concentration is measured in so called ppm units. Ppm – Parts per million