Carbon monoxide

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Carbon monoxide (CO), also called carbonous oxide, is a colorless, odorless and tasteless gas which is slightly lighter than air. It consists of one carbon atom and one oxygen atom, connected by a covalent double bond and a dative covalent bond. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal biological functions.[1][2]

Carbon monoxide is a major atmospheric pollutant in some urban areas, chiefly from the exhaust of internal combustion engines (including vehicles, portable and back-up generators, lawn mowers, power washers, etc.), but also from improper burning of various other fuels (including wood, coal, charcoal, oil, paraffin, propane, natural gas, and trash). Carbon monoxide is also released in coal mining, particularly mountaintop removal mining, due to the use of explosives, which pollutes the air and poses a health risk for mine workers.[3] CO is also released from coal plants: According to the Union of Concerned Scientists, in an average year, a typical coal plant (500 megawatts) generates 720 tons of carbon monoxide, which causes headaches and places additional stress on people with heart disease.[4]


Carbon monoxide is produced from the partial oxidation of carbon-containing compounds; it forms when there is not enough oxygen to produce carbon dioxide (CO2), such as when operating a stove or an internal combustion engine in an enclosed space. In presence of oxygen, carbon monoxide burns with a blue flame, producing carbon dioxide.[5] Coal gas, which was widely used before the 1960s for domestic lighting, cooking and heating despite its toxicity, had carbon monoxide as a primary constituent. Some processes in modern technology, such as iron smelting, still produce carbon monoxide as a byproduct.[6]

CO and smog

Carbon monoxide is part of the series of cycles of chemical reactions that form smog. Along with aldehydes, it reacts photochemically to produce peroxy radicals, which oxidize nitrogen oxide (NO) to nitrogen dioxide (NO).2. Although this creation of NO2 is the critical step leading to low level ozone formation, it also increases this ozone in another, somewhat mutually exclusive way, by reducing the quantity of NO that is available to react with ozone.[7]

Simplified, the net effect of the ozone cycle is:
CO + 2O2 → CO2 + O3


The EPA Office of Air Quality Planning and Standards (OAQPS) has set National Ambient Air Quality Standards under the Clean Air Act for six principal pollutants, which are called "criteria" pollutants: sulfur dioxide, particulate matter, nitrogen oxides, ozone, lead, and carbon monoxide. After the EPA sets or revises each standard and a timeline for implementation, the responsibility for meeting the standard falls to the states. Each state must submit an EPA-approved plan that shows how it will meet the standards and deadlines. These state plans are known as State Implementation Plans (SIPs)." [8]



  1. Omaye ST. (2002). "Metabolic modulation of carbon monoxide toxicity". Toxicology 180 (2): 139–150. doi:10.1016/S0300-483X(02)00387-6. PMID 12324190. 
  2. "Rate of formation of carboxyhemoglobin in exercising humans exposed to carbon monoxide." (1992). Journal of applied physiology (Bethesda, Md. : 1985) 72 (4): 1311–9. PMID 1592720. 
  3. "The Dirty Truth about Coal: Mining", Sierra Club, June 2007.
  4. "Coal Power: Air Pollution," Union of Concerned Scientists, accessed August 2008
  5. Carbon Monoxide - Molecule of the Month, Dr Mike Thompson, Winchester College, UK
  6. Robert U. Ayres, Edward H. Ayres (2009). Crossing the Energy Divide: Moving from Fossil Fuel Dependence to a Clean-Energy Future. Wharton School Publishing, 36. ISBN 0137015445. 
  7. (1977) Ozone and other photochemical oxidants. National Academies, 23. ISBN 0309025311. 
  8. "NAAQS" Sierra Club, accessed July 2010.

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External links

Wikipedia also has an article on Carbon monoxide. This article may use content from the Wikipedia article under the terms of the GFDL.