Carbon Monoxide

It is produced naturally by a wide variety of processes, perhaps the best known of which is the incomplete combustion of carbonaceous (carbon-containing) fuels (trees, grass, brush, and so on).

When such fuels burn in the absence of sufficient oxygen to oxidize all the carbon present in the fuel (which is almost always the case in the real world), some of the carbon is converted to carbon monoxide.

 

Carbon monoxide is also produced by living green plants that are exposed to sunlight, from dead and decaying plant matter, from the soil and wetlands, from rice paddies, and from bacteria, algae, jellyfish, and other organisms that live in the oceans.

The gas is also produced indirectly in a complex sequence of reactions that begins when methane in the atmosphere reacts with hydroxyl radicals, forming formaldehyde (HCHO) and then carbon monoxide:

Amount of carbon monoxide in the atmosphere has been estimated at about 3.06 million short tons (2.78 million metric tons).

Of this, about half (1.438 million metric tons) is produced naturally and about half (1.350 million metric tons) through anthropogenic (human-made) sources.

Naturally occurring carbon monoxide is not generally regarded as an environmental problem because it is so widely spread at very low concentrations (about 0.1 ppm) throughout the atmosphere.

If anthropogenic carbon monoxide were also distributed equally throughout the atmosphere, it would contribute little to any natural health risks posed by the gas.

The problem is that the carbon monoxide from anthropogenic sources tends to accumulate at dangerously high concentrations in certain geographic locations, such as urban centers. In such cases, the level of carbon monoxide to which humans and other organisms are exposed may be sufficiently great to pose a significant health hazard.

Other sources of the gas are industrial processes (such as metal production and chemical manufacturing), fireplaces and woodstoves, aircraft, and electrical power generating plants.

Carbon monoxide concentrations tend to fluctuate throughout the year, with higher concentrations observed in the winter. One reason for this trend is the greater use of fuels for heating.