With a small amount in the atmosphere (400 ppmv - part per million by volume), carbon dioxide is a chemical molecule composed of one carbon atom and two oxygen atoms whose formula is CO2. Under normal conditions of temperature and pressure, it is a colorless, odorless, incombustible, non-reactive gas, but soluble in water.

It is present in four phases: solid, liquid, gaseous and supercritical, depending on temperature and pressure conditions, and can be directly marketed under its first three forms.

The special properties of carbon dioxide include its inertness and its high solubility in water. Carbon dioxide gives beverages their sparkling freshness, is used in the treatment of drinking water and provides an alternative to aggressive acids for wastewater neutralisation. In cryogenic, liquid and solid form, CO2 turns into dry ice, which is suitable for use as a refrigerant or as a cleaning medium (for dry ice blasting).