Carbon monoxide is a gasCarbon monoxide is a colorless, nonirritating, odorless, and tasteless gas. It is found in both outdoor and indoor air.
Sources of carbon monoxide in the atmosphereCarbon monoxide is made when carbon in fuel is not burned completely. Carbon monoxide is produced from both human-made and natural sources. The most important human-made source of carbon monoxide arises from the exhaust of automobiles.

Inside homes, improperly adjusted gas appliances, furnaces, wood burning stoves, and fireplaces are a potential source of carbon monoxide (see Section 1.3).

Carbon monoxide is released from wood burning/volcanoes/forest fires.
Industrial usesCarbon monoxide can be used in industry to synthesize many compounds such as acetic anhydride, polycarbonates, acetic acid, and polyketone.

From: 1, PUBLIC HEALTH STATEMENT

Cover of Toxicological Profile for Carbon Monoxide
Toxicological Profile for Carbon Monoxide.
Wilbur S, Williams M, Williams R, et al.

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