ATMOSPHERIC SULFUR AND ITS LINKS TO THE BIOTA 



161 



ATMOSPHERE 



PEDOSPHERE AND HYDROSPHERE 

 Fig. 1 The circulations of sulfur through the atmosphere and the biota. 



Hydrogen sulfide, containing sulfur in its most reduced form, originates, as 

 indicated earlier, from the nonspecific reduction of organic sulfur and from 

 sulfate reduction by anaerobic bacteria. These are thought to be the principal 

 processes by which H 2 S is generated on a global scale. In relatively small 

 amounts H 2 S is derived from industrial processes, such as petroleum refining and 

 kraft pulp manufacture, and from volcanoes. In the atmosphere, H 2 S may 

 undergo oxidation by atomic oxygen and ozone to yield S0 2 and ultimately 

 sulfate. In a rural atmosphere the concentration of H 2 S has been found 4 to be 

 of the order of 0.3 jUg/m 3 , but the method used has been challenged, and actual 

 background concentrations are presumed to be significantly lower than this 

 value. (See the section on Emission of Biogenic Hydrogen Sulfide.) The 

 residence time of H 2 S in the atmosphere is estimated not to exceed 1 day and is 

 probably considerably less than 1 day. 



Sulfur dioxide is produced in the atmosphere as a product of H 2 S oxidation. 

 It is emitted into the atmosphere in large quantities as a product of fossil-fuel 

 combustion and of ore smelting and in lesser quantities from volcanic action. 

 Coal burning is the major source of S0 2 from fossil fuels. Within the 



