Which form of carbon is released into the atmosphere?

• A. Carbon monoxide
• B. Carbon dioxide
• C. Methane
• D. Ammonia

Answer: (B)

When carbon enters the atmosphere, it most commonly appears as carbon dioxide. This form is produced in large amounts by burning fossil fuels for energy and transportation, and also by natural processes like plant and animal respiration and the decomposition of organic matter. Carbon dioxide is a stable, long-lived gas in the air and a major greenhouse gas, which is why it’s the form most associated with atmospheric carbon.

Carbon monoxide is CO and comes mainly from incomplete combustion; it’s a pollutant but not the main carbon-containing gas in the atmosphere. Methane also contains carbon and is released in certain natural and human-made processes, and it is a potent greenhouse gas, but it is emitted in smaller quantities than carbon dioxide in many contexts. Ammonia contains no carbon at all, so it isn’t a form of carbon released into the atmosphere.