Carbon Dioxide

Carbon dioxide (chemical formula CO₂) is a colorless and odorless gas when pure. Each molecule consists of one carbon atom bonded to two oxygen atoms, arranged in a linear structure. It is a trace gas in Earth's atmosphere but plays a major role in life and surface temperature.

CO₂ is produced by the respiration of living organisms, the burning of carbon-containing materials such as fossil fuels and biomass, and volcanic activity. It is taken up by plants through photosynthesis, and the ocean absorbs part of it as well. This exchange is known as the carbon cycle.

Physical and Chemical Properties

CO₂ is denser than ordinary air and can accumulate in low-lying enclosed spaces. At normal pressure it has no liquid state: it transitions directly from solid to gas (sublimation). Its solid form is known as dry ice and is used for cooling. When dissolved in water it forms weak carbonic acid, making the water acidic.

Role in Atmosphere and Climate

CO₂ is one of the greenhouse gases: it absorbs and re-emits infrared radiation leaving Earth, raising surface temperature. Since the onset of industrialization, atmospheric CO₂ levels have risen, largely attributed to the burning of fossil fuels and changes in land use such as deforestation. The increase is a major factor in the climate change debate.

Uses and Health

CO₂ is used in carbonated beverages, fire extinguishers, food processing, and certain refrigeration applications. The human body constantly produces CO₂ which is exhaled in breath; blood levels of it help regulate breathing. When it accumulates in an enclosed space, it can cause headache, shortness of breath, and respiratory distress, since it displaces oxygen.