ATMOSPHERIC CARBON MONOXIDE 137 



but there has been little interest in it as a pollutant except when CO 

 concentrations were high enough to produce acute physiological effects. Interest 

 has been stimulated recently by evidence that there are chronic as well as acute 

 physiological effects and by recognition that CO takes part in complex chemical 

 reactions in air. Work has been stimulated by development of analytical 

 techniques capable of resolving CO concentrations in the range of fractions of a 

 part per million in air. 



SOURCES OF CO 



Until recently it seemed well established that man's activities were the main 

 sources of CO in the atmosphere. Now there is growing evidence that the oceans 

 are also an important source. According to Robinson and Robbins, the total 

 worldwide CO emission from combustion is 285 X 10 6 tons or about 

 2.6 X 10 1 4 g. Automobiles are the major source, accounting for about 68% of the 

 total produced by combustion. This value was based on the assumption that 

 2.91 lb of CO are produced per gallon of gasoline and that the annual worldwide 

 gasoline production in 1966 was 379 X 10 6 tons. Other important sources by 

 man are fuel combustion in stationary sources, industrial processes, and 

 solid-waste disposal. Detailed estimates by source category are given in the 

 literature. 1 ' 2 



The chemical reactions that occur in photochemical smog produce CO. 

 Results of investigations of such production have been summarized by Altshuller 

 and Bufalini. The yields for most of the olefins and aromatic hydrocarbons 

 reacted in "synthetic" smog are about 0.2 mole of CO per mole of hydrocarbon 

 reacted. If we assume that about 2% of the gasoline burned in an automobile is 

 emitted as unburned hydrocarbons in the exhaust, that half of this unburned 

 gasoline takes part in photochemical reactions, and that the average molecular 

 weight of the gasoline is 120, the yield of CO is 10~ 4 times the amount of 

 gasoline consumed by automobiles. And if we assume, as was done earlier, that 

 the worldwide annual production of gasoline is 379 X 10 tons, the yield of CO 

 formed photochemically from unburned gasoline would be 379 X 10 2 tons, an 

 insignificant figure compared with the amounts produced by combustion. 



Man's contribution to the CO content of the atmosphere is much greater in 

 the Northern than in the Southern Hemisphere because 95% of world gasoline 

 consumption occurs in the Northern Hemisphere. 



Perhaps the most obvious natural sources of CO are forest, brush, and grass 

 fires. Robinson and Robbins 2 estimated an annual worldwide emission from 

 forest fires of 11 X 10 6 tons. 



Recent research on the oceans as a source of CO has been reviewed by Seiler 

 and Junge and by Junge, Seiler, and Warneck. 5 Compelling evidence was 

 obtained by Swinnerton, Linnenbom, and Check 6 that surface waters of the 

 western Atlantic Ocean are supersaturated with CO. Swinnerton, Linnenbom, 



