CO₂ at a glance: What it is, why it is produced, and how to maintain healthy levels indoors

What is CO₂?

CO₂ is a colorless and odorless gas consisting of one carbon atom and two oxygen atoms. It occurs naturally in the atmosphere and is an important component of biological and chemical processes. CO₂ is produced, among other things, by human respiration, combustion processes, and the biological decomposition of organic matter. It is essential for plants, as they need it for photosynthesis. Outdoor air typically contains between 400 and 450 ppm of CO₂.

How is CO₂ produced indoors?

CO₂ concentrations can vary greatly indoors. Human respiration is the largest source: each person produces around 15 to 20 liters of CO₂ per hour. CO₂ accumulates particularly quickly in modern, well-sealed buildings, as natural air exchange is restricted. Other sources include combustion processes such as candles, fireplaces, or gas stoves. Room size, the number of people, and air circulation also influence CO₂ concentrations: small, heavily used rooms with closed doors heat up more quickly, allowing CO₂ to accumulate locally.

Normal CO₂ levels indoors

CO₂ is measured in ppm (parts per million). The following values serve as a guide:

Workplace guidelines and health organizations recommend staying below 1000 ppm at all times.

Effects of excessive CO₂ levels

Increased CO₂ concentrations have a direct effect on the body. Many people experience fatigue, concentration problems, headaches, and a feeling of "heavy air" long before they know the cause. Although CO₂ does not displace oxygen, the body is sensitive to changes. Studies show that very high levels can reduce performance by up to 50 percent.

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CO₂ as an indicator of air quality

CO₂ itself is not toxic, but it serves as a reliable indicator of indoor air quality. High levels indicate that the air is stale and often also that there is increased exposure to aerosols. Rooms with high CO₂ concentrations are less likely to have sufficient fresh air supply, which can increase the risk of infection, especially in schools, offices, or public transportation.

5 tips for healthy CO₂ levels

1. Ventilate thoroughly instead of tilting: Windows should be opened completely instead of just tilted.
2. Ventilate before and after the meeting: Rooms where many people are present at the same time are the quickest to reach critical levels.
3. Let fresh air in when cooking or heating: Combustion processes significantly increase CO₂ levels, which is why brief bursts of ventilation are essential for healthy indoor air.
4. Leave doors open if possible: this allows CO₂ to disperse and reach the nearest ventilation point more quickly.
5. Use air quality monitors: A device such as the air-Q not only displays the CO₂ level, but also warns you when values reach dangerous levels.