138 CADLE 



and Lamontague 7 found at two places in the Atlantic that the CO concentration 

 in water varied daily, indicating a biotic origin. Robinson and Robbins 2 ' 8 

 analyzed near-surface air over the Pacific Ocean during several cruises. They 

 observed CO concentrations in the Southern Hemisphere about one-half to 

 one-third those in the mid-latitudes of the Northern Hemisphere and also 

 observed weak diurnal cycles, with lower concentrations occurring in early 

 afternoon and higher concentrations at night. These results seem to indicate that 

 the oceans are a CO source. Seiler and Junge 9 measured CO concentrations near 

 the tropopause and found a decrease with increasing altitude above the 

 tropopause, but their tropospheric measurements failed to show the differences 

 in CO concentrations between the Northern and Southern Hemispheres reported 

 by Robinson and Robbins. Later they also found that seawater is 

 supersaturated with CO. Junge et al. 5 estimated the amount of CO released from 

 the oceans to be about 29% of the total of man's emissions. Swinnerton et al. 7 

 earlier had obtained a figure of 5%. The oceans appear to be an important 

 biogenic source of CO. 



Vegetation may also contribute to the CO content of the atmosphere, but 

 little is known about this possibility. Wilks 1 ° found that green plants grown in a 

 closed, illuminated system (plastic bags) emit small amounts of CO. Also, finely 

 divided powder and chlorophyll extracts of green plants, when illuminated in an 

 atmosphere of oxygen and water vapor, emitted both CO and aldehydes. 



Volcanic action is another natural source of CO. A very crude idea of the 

 average annual emission can be obtained by making the entirely unsubstantiated 

 assumption that all volcanoes emit CO in the same amounts relative to the 

 amounts of lava (including pyroclastic materials). Then, using the same approach 

 as was used by Kellogg et al. l to estimate annual SO2 emissions and using the 

 data of Shepherd for the composition of Kilauea volcano (Hawaii) gases, we 

 see that the annual volcanic emission of CO is about 7.5 X 10 4 tons. This 

 quantity is insignificant compared with the emissions from combustion. 



Another possible, but highly speculative, natural source of CO is the 

 sequence of chemical reactions that produce CO in photochemical smog but 

 involve the organic vapors (essential oils) evolved by plants and naturally 

 produced oxides of nitrogen. Such vapors are emitted by many species of plants, 

 and hundreds of organic compounds have been identified in essential oils. Such 

 photochemical reactions may be responsible for much natural haze, such as that 

 which forms over the jungles of Colombia. Rasmussen and Went 1 estimated the 

 worldwide emission of such vapors to be 4.4 X 10 8 tons/year, but Ripperton, 

 White, and Jeffries 1 4 suggest that this estimate may be too low by a factor of 2 

 to 10. If we assume that the annual emission of such vapors is 10 9 tons/year, 

 that the molar yield of CO is 0.2, that (as just mentioned) half of the essential 

 oils take part in photochemical reactions, and that the average molecular weight 

 of the essential oils is 140, then the annual production from these reactions is 

 20 X 10 6 tons. 



