CO₂ monitoring

Characteristics of CO₂

Carbon dioxide - CO₂ for short - is a chemical bond made up of the elements carbon and oxygen. In nature, CO₂ occurs as a colorless and unscented gas. It is not explosive, and as a natural component of the air we breathe, at normal concentrations, it is completely harmless. CO₂ is used in various ways for everyday applications, for instance as carbonation in drinks, for cooling in air-conditioning systems, and as a solvent for cleaning. It is also used in fire extinguishers. However, too-high concentrations can have a harmful effect on people and animals, in part because of the displacement of oxygen in the air. The CO₂ content of air is normally about 380 ppm, or 0.038%. Above a concentration of 1%, CO₂ begins to have a physiological effect. A 5% concentration of CO₂ in inhaled air can create headaches and dizziness; 8% will result in death within 30 to 60 minutes. This is why accidents frequently occur in wine cellars, wells and feed silos, where increased CO₂ concentrations can occur as a result of fermentation processes. However, natural CO₂ emissions, for instance in the Eifel region, also show that this does not necessarily pose an increased risk to the environment. When CO₂ is emitted at the earth's surface, depending on controlling conditions such as flow rate, landscape, wind speed and wind direction, it can quickly mix with the surrounding air and be reduced to a harmless concentration.

In order to counteract climate change, geological storage would need to prevent CO₂ from entering the environment for thousands of years. However, this raises the question of whether such long-term storage is possible without posing a risk to people and the environment. In addition to carefully choosing an appropriate location, this involves making reliable predictions about storage security and the corresponding monitoring options.

The storage sites must be monitored for the following reasons (Kühn, 2011):

1. Safety and environmental protection reasons: It must be ensured that people, animals and the ecosystem are not endangered or negatively affected, and that the climate-protection goals are met.
2. Societal reasons: Complete transparency is needed about the details of the safety of the storage operation in order to build the necessary trust within the population.
3. Financial reasons: The actual amount of CO₂ kept in the storage space must be monitored so that it can be written off as "prevented emissions" in the EU's emission trade program.
4. Operational reasons: For controlling and optimizing the injection process.