ATMOSPHERIC CARBON MONOXIDE 



RICHARD D. CADLE 



National Center for Atmospheric Research,* Boulder, Colorado 



ABSTRACT 



Carbon monoxide (CO) is a colorless, odorless gas produced principally by combustion of 

 organic substances. It is probably also produced by bacterial action on land and in the 

 oceans. Concentrations in the "natural" troposphere average 0.1 to 0.2 ppMv (parts per 

 million by volume). In smoggy city air 40 ppMv is common. The mechanisms of removal of 

 CO from the atmosphere are not well known but seem to include chemical reactions in both 

 the troposphere and stratosphere and bacterial action at Earth's surface. 



Carbon monoxide (CO) is a colorless, tasteless, and nearly odorless gas. It is 

 slightly soluble in water, about 2.5 ml in 100 ml of water at 19°C and 760 torrs. 

 Its melting point is -199°C, and its boiling point is -191. 5°C. It has been 

 considered "inactive" chemically with respect to most substances unless heated 

 considerably above 300° K or in the presence of a suitable catalyst. 



The toxicity of CO to man results from its ability to combine with the 

 hemoglobin of the blood, preventing the hemoglobin from combining with 

 oxygen. The reaction is reversible, but the affinity of hemoglobin for CO is more 

 than 200 times that for oxygen. Early symptoms are headache and nausea. 

 Unconsciousness is produced in about an hour by 0.2 vol.% CO in air; 1.0 vol.% 

 is reported to be rapidly fatal. Much less is known about chronic effects of CO, 

 but long-term exposure of animals to CO seems to produce morphological 

 changes in the heart and brain 1 and may cause increased hemoglobin levels. 



Plants are relatively insensitive to CO. Alterations of plant characteristics 

 have been reported by exposures 1 exceeding 10,000 ppMv CO. 



Carbon monoxide emission is one of the oldest problems of air pollution. 

 Poisoning by CO apparently has been reported in Greek and Roman literature. 



•The National Center for Atmospheric Research is sponsored by the National Science 

 Foundation. 



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