ATMOSPHERIC SULFUR AND ITS LINKS TO THE BIOTA 177 



they have measured its rate of emission from marine algae, living and dead tree 

 leaves, and terrestrial soils. Average emission rates from algae were of the order 

 of 70 picaliters g 1 hr ! and from leaves and soils, 60 X 10 12 gg ! hr 1 . The 

 standard deviations for all these measurements were large. So far Lovelock et al. 

 have been unable to detect dimethyl sulfide in the atmosphere, although they 

 state that failure to do so may have been due to oxidation occurring between 

 collection and analysis of samples. 



As noted by Lovelock et al. in Ref. 41, Bentley et al. 42 have found the 

 spectrum of the products of the simulated atmospheric photooxidation of 

 dimethyl sulfide to include dimethyl sulfoxide, methane sulfonic acid, sulfur 

 dioxide, and sulfuric acid. Lovelock et al. suggest that, since dimethyl sulfoxide 

 may be one of the first products appearing in the oxidation reaction, its low 

 volatility and hygroscopic nature may cause it to be readily removed from the 

 atmosphere before further oxidation. If so, then dimethyl sulfide would be less a 

 source of sulfate aerosol than are the inorganic sulfur compounds, H 2 S and S0 2 . 



It should be noted that a number of plant families are known to have 

 methylated sulfur compounds as constituents. 43 Also, Starkey 44 and his 

 students have shown that, in the dissimilation of methionine brought about by 

 certain bacteria or bacteria and fungi, the volatile sulfur compounds methyl 

 mercaptan and dimethyl disulfide appear as products. 



Up to now the characterization of the biogenic sulfur-compound emission 

 process has been in part held back by the lack of sufficiently sensitive analytical 

 methods for the measurement of the concentrations of H 2 S, and now of other 

 compounds such as dimethyl sulfide, in the atmosphere. For H 2 S, 

 background concentrations have been assumed to be of the order of 0.3 Atg/m 3 

 or less, whereas available analytical methods could not measure concentrations 

 less than about 1.5/Jg/m . Recently a method has been devised which is 

 reported to permit measurement of concentrations as small as 0.002 jug/m . 

 This method involves collecting the H 2 S on AgN0 3 -treated filter paper, 

 recovering the resulting Ag 2 S from the filter paper with alkaline cyanide 

 solution and analyzing for the released sulfide ion fluorometrically. When this 

 method was used in unpolluted air in Colorado, concentrations in the range of 

 0.03 to 0.1 jUg/m were found. For dimethyl sulfide and, presumably, other 

 related sulfur compounds, sensitive gas chromatographic methods of analysis 

 evidently are available and will soon be described in the literature. 



In view of the analytical developments just described, studies of the emission 

 of biogenic sulfur compounds now appear feasible. Such studies might involve 

 the measurement of vertical fluxes of these compounds into the atmosphere 

 along with the establishment of profiles of physical, chemical, and micro- 

 biological properties of the locale of generation and emission. 



In certain coastal regions, emissions of what is presumed to be biogenic H 2 S 

 are so strong as to blacken paint and tarnish silver in nearby homes. Emission 

 rates and other features of the overall emission process which apply to these 

 areas should be readily observable. 



