carbondioxide

Carbon dioxide, with the chemical formula CO2, is a colorless, odorless gas at standard conditions. It is a linear molecule consisting of one carbon atom double-bonded to two oxygen atoms (O=C=O). It is nonflammable and slightly denser than air.

In nature, CO2 is part of the carbon cycle. It occurs in the atmosphere at about 0.04% by volume (roughly 400 parts per million). It is released by respiration in animals and plants, combustion of organic material including fossil fuels, fermentation, and volcanic activity. It is absorbed by oceans and by photosynthesis in plants. Human activities, especially burning fossil fuels and deforestation, have increased atmospheric CO2 concentrations and contributed to climate change. The residence time of CO2 in the atmosphere spans decades to centuries, making it a long-lived greenhouse gas.

Common applications include carbonation of beverages and use as dry ice for cooling. CO2 serves as a chemical feedstock in the production of various materials, including urea and methanol, and is central to carbon capture and storage initiatives. It is also used as a working fluid in certain refrigeration systems (R-744) and in enhanced oil recovery.

Safety and environmental considerations: CO2 is not toxic at low concentrations but can cause asphyxiation in enclosed or poorly ventilated spaces by displacing oxygen. Occupational exposure limits are established in many jurisdictions, and proper ventilation, monitoring, and handling procedures are important for safety.