Here are four different ways chemists use to show a molecule of carbon monoxide. In the colored molecule models, carbon is light gray and oxygen is red.
Carbon Monoxide - CO
Carbon monoxide is kind of gas. It is poisonous. A molecule of carbon monoxide (CO) has one carbon atom and one oxygen atom. Earth's atmosphere has a small amount of carbon monoxide in it.
The carbon monoxide in air comes from nature and from things people do. Volcanoes and forest fires give off carbon monoxide. Most of the carbon monoxide people make comes from the engines of cars and trucks. Carbon monoxide is an important kind of air pollution.
When fuel burns, it usually makes carbon dioxide (CO2). Sometimes when fuel burns there isn't enough oxygen, or there is too much carbon. When this happens, the burning creates carbon monoxide, too.
Earth is not the only place we find carbon monoxide. It has been found in gaseous nebulae, in the atmospheres of other planets, and in the ices of comets.