Carbon dioxide emissions also pollute indoor air. The higher the atmospheric carbon dioxide concentration rises, the more difficult it becomes to maintain fresh indoor air.
The building must be designed and constructed as a whole to ensure a healthy, safe, and comfortable indoor climate in the occupancy zone under all typical weather conditions and usage situations. Building regulations set a guideline value of a maximum of 1200 ppm for carbon dioxide.
A concentration of 1200 ppm is not dangerous, but it is a reasonable target that still provides a safety margin against immediately harmful concentrations. An elevated carbon dioxide concentration is usually a sign that ventilation is not working efficiently enough, and concentrations of other harmful substances may also be elevated. In practice, in classrooms, daycare centers, and e.g. carbon dioxide concentrations in meeting rooms can rise significantly above that 1200 ppm level, causing harm, such as a decline in mental performance. If the room’s ventilation is particularly poor, concentrations may rise to much higher levels and already cause significant harm to people’s health and comfort. Certainly, many other factors also impair indoor air quality, but according to studies, even a mere increase in carbon dioxide concentration causes harm. Even a 1000 ppm carbon dioxide concentration in indoor air appears to slightly impair mental performance, and the harms increase as concentrations rise.
Efforts are made to maintain good indoor air quality through ventilation. As atmospheric carbon dioxide concentration increases, maintaining good indoor air continuously becomes more difficult. Before the start of the industrial revolution, the outdoor air carbon dioxide concentration was approx. 280 ppm and currently already approx. 400 ppm. According to forecasts, this century could see figures close to 800 ppm, and according to many estimates, even higher. Consequently, keeping indoor CO2 concentrations at a low level will become almost impossible with current methods by the end of the century, and will become significantly more difficult much earlier.
Ventilation must be continuously enhanced as the concentration difference between outdoor air and the desired indoor air decreases.
Keeping carbon dioxide concentrations in classrooms and office spaces below the 1200 ppm level becomes significantly more difficult if the concentration of outdoor air used for ventilation is, for example, 800 ppm instead of the current less than 400 ppm. Problems are exacerbated when the temperature of the ventilated space differs significantly from the outdoor temperature. On a cold winter day, the amount of energy required for ventilation and heating increases because there is more air to be exchanged and heated. Ventilation requirements, energy consumption, and costs will therefore rise in the future. In spaces with gravity ventilation, maintaining good indoor air becomes difficult, if not impossible.
If the use of fossil fuels continues at the current accelerating pace for a long time, the atmospheric carbon dioxide concentration will eventually rise above 1000 ppm, and even the outdoor air will start to feel stuffy. It should be emphasized that ventilation is necessary for many other reasons than elevated indoor carbon dioxide concentration, but carbon dioxide can be expected to cause greater indoor air quality problems in the future than currently. Generally healthy, fit people probably tolerate higher carbon dioxide concentrations than those suffering from cardiovascular and respiratory diseases. The health effects of rising indoor carbon dioxide concentration and potential needs for developing ventilation technology should be studied to clarify the true scale of the problem. Additionally, it should be assessed how lifelong exposure to high carbon dioxide concentrations affects human health.
Stuffy indoor air is, however, a small and distant problem compared to climate change and ocean acidification caused by elevated atmospheric carbon dioxide concentration. To avoid all these problems, we must strive to eliminate the use of fossil fuels as quickly as possible.
Esko Pettay
