ATMOSPHERIC SULFUR AND ITS LINKS TO THE BIOTA 163 



oxidized to sulfate. The extent to which these hydrogen ions persist depends on 

 the extent to which basic substances are present in the water droplet. In any 

 case, acidity present to some degree in precipitation in association with sulfate 

 ion may be expected and is often found. 



The Global Atmospheric Sulfur Budget 



Global budgets have recently been prepared by a number of writers. 2 ' 3 ' s ' 7 ' 8 

 The principal sources and sinks and their transfer rates as derived by Kellogg and 

 coworkers 3 are given in Table 1 . Transfer rates in Table 1 and elsewhere in the 

 paper are given in units of millions of metric tons of sulfur per year. Details of 

 the derivation of the transfer rates in this and other tabulations will not be given 

 here but may be found in the original papers. The following comments, however, 

 are of present interest. 



The anthropogenic mobilization of sulfur represented by fertilizer applica- 

 tion amounts to 26 million tons/year according to recent estimates. 8 Estimates 

 of emission into the atmosphere resulting from human activity range from 50 to 

 70 million tons/year. Thus the contribution to the atmosphere represents the 

 major fraction of human mobilization. 



Over 90% of man-made emissions come from the northern hemisphere, and 

 thus the distribution of these emissions is highly nonuniform. Man-made 

 emissions doubled in the period from 1940 to 1965. It is projected that the 

 present rate will more than double by the year 2000. 



TABLE 1 



GLOBAL ATMOSPHERIC SULFUR BUDGET 3 



Transfer rate, 10 6 tons S/year 



Terrestrial Marine Total 



Sources 



Human activity 50 50 



Biogenic H 2 S 90 90 



Sea-spray sulfate 43 43 



Total 183 



Sinks 

 Precipitation and 

 dry deposition 96 72 168 



2 



Absorption of S0 2 



by vegetation 



and soils 15 15 



Absorption of S0 2 



by oceans ? 



Total 183 



