Carbon dioxide is one of the more frequent found gases on the earth. It is a by-product of combustion processes and the natural metabolism of living organisms. We inhale oxygen and exhale carbon dioxide. The carbon dioxide level in exhaled air is rather constant about 3,8 % (38.000 ppm). When carbon dioxide is exhaled it will quickly be mixed with the surrounding air and, if the ventilation is good, the concentration will be reduced to harmless levels. Indoor CO2 levels usually vary between 400 and 2000 ppm (parts per million). Outdoor CO2 levels are usually 350 - 450 ppm. Heavily industrialized or contaminated areas may periodically have a CO2 concentration of up to 800 ppm. The levels of outdoor CO2 are higher in areas where traffic is very heavy. CO2 must not be confused with carbon monoxide (CO), a very toxic gas that is a by-product from poor combustion in i.e. cars and fireplaces. Carbon monoxide is dangerous at very low concentrations (25 to 50 ppm).
Is CO2 an indoor air pollution? Carbon dioxide is not seen as an indoor air pollution but it is a suitable tracer gas for indicating possible micro-organisms generated by people that contributes to deteriorated comfort.This is why a higher level of pure CO2 is permitted in industrial environments, than in buildings where people- generated micro-organisms and CO2 is the principal concern. In industrial environments where process generated CO2 dominates (or CO2 not generated by people), Even if CO2 itself is not dangerous in normal concentrations it is frequently used as a reference and an indicator of indoor air quality and therefore ventilation performance. That is due to the fact that people, when they exhale CO2, also exhale and emit many other micro-organisms. These micro-organisms may be gases, odours, particles and germs. When the concentration of these micro-organisms, as a result of bad ventilation, is permitted to increase in a room, occupants complain of tiredness, headache, and even worse; feeling of sickness. Carbon dioxide itself does not give these problems until high levels are developed. High CO2 levels in a room occupied by a lot of people indicates that the air is likely to be contaminated.
