32 



for domestic heat and the controlled burning of forests and rangeland 

 also contribute a small amount of S to the atmosphere. 

 1.2.2.2 Biogenic sources 



Natural sources of atmospheric S, unrelated to human activity, 

 include the decomposition and combustion of organic matter, spray from 

 the oceans, and volcanic and other geo thermal activity. Seawater is 

 one of our greatest natural sinks for S and also one of our greatest 

 sources. The average concentration of sulfate in the oceans is 2.65 

 ppm. The concentration of H S cannot be detected in seawater; the 

 oceans are supersaturated with dimethyl sulfide (Cadle, 1975), but it 

 is doubtful if any of this S escapes into the atmosphere in the sulfide 

 form. The sulfate released annually from the surface of oceans has 

 been estimated to be around 40 to 130 million metric tons, but only 

 10% of this passes over land (Eriksson, 1959, 1960; Friend, 1973). 



Vegetative decay under anaerobic conditions releases large quanti- 

 ties of H S to the atmosphere where it is rapidly oxidized. Freshwater 

 swamps and salt water marshes are abundant sources of biologically- 

 produced atmospheric S. These sources are difficult to quantitate, 

 and most estimates seem to be based on the theoretical need to balance 

 the S cycle. Gaspar (1975) reviewed literature which indicated 30 to 

 202 million metric tons of H„S released by biological decay on land. 

 Edgerton et al . (1980) compiled estimates of biogenic S emitted from 

 wetlands in Florida (Table 4) . 



1.2.3 Local and Regional Studies of 

 Rainfall and Atmospheric S 



Recent studies by Edgerton et al. (1980) and Brezonik et al . 



(1980) have helped to delineate the areas of acid precipitation in 



