METEOROLOGY AND ATMOSPHERIC CHEMISTRY 



89 



TABLE 12 



Estimate of Annual Atmospheric Deposition of 

 n-Cio to n-Cao Alkanes to the Ocean at Enewetak" 



Deposition 

 mechanism 



Deposition rate, 

 lO'^gcm^yr' 



Particulate: 

 Wet 

 Dry 



VafKjr Phase: 

 Wet 

 Dry 



Total 



6.2 to 62 

 0.8 to 8 



to 0.00001 

 Oto 1.4 



7 to 71 



'From Duce and Gagosian, 1982. 



TABLE 13 



Concentration of Fatty Alcohols, Fatty Acid Esters, and 

 Fatty Acid Salts on Atmospheric Particles at Enewetak" 



Organic 

 substance 



Concentration range, 

 pg m~^ 



Fatty alcohols 



C21"C32 



Fatty acid esters 

 C13-C20 



C21~C32 



Fatty acid salts 

 C13-C20 



C21~C32 



'From Gagosian et al., 1981b. 



1981b, 1982). These authors suggest, on the basis of 

 odd/even carbon concentration ratios and the concentra- 

 tion distribution observed, that the fatty alcohols and the 

 C21 to C32 fractions of the fatty acid esters and fatty acid 

 salts have a natural terrestrial source, whereas the lighter 

 Ci3 to C20 fatty acid esters and fatty acid salts in the 

 Enewetak atmosphere likely have a marine source. 



Heavy Chlorinated Hydrocarbons and 

 Other Synthetic Organics 



A number of synthetic organic substances were mea- 

 sured in the Enewetak atmosphere, including PCBs and 

 certain pesticides and plasticizers (Atlas and Giam, 1981). 

 The concentrations observed in the vapKjr phase are 

 presented in Table 14. Concentrations of these substances 

 on aerosols were less than 10% of the vapor phase con- 

 centrations. Altas and Giam (1981) point out that rain may 

 not be the primary mechanism for removal of these vapor 

 phase organic substances from the air. Direct vapor 

 exchange with the ocean may be most important. By using 

 a vapor deposition velocity of 8 m h ' for PCB 1242, 

 the direct vapor exchange PCB flux to the ocean at 

 Enewetak would be 35 X 10 '° g cm"^ yr"^ This is at 

 least 50 times greater than the precipitation flux of 

 <0.8 X 10"'° g cm^^ yr"' for Aroclor 1242, which can 

 be calculated using the concentrations in Table 14 and the 

 annual rainfall amount in Fig. 2a. The vapor phase flux 

 would result in a PCB Aroclor 1242 atmospheric residence 

 time of about 30 days, which would explain the relatively 

 uniform concentration distribution of Aroclor 1242 over 

 the Atlantic and Pacific Oceans and nonurban continental 

 areas (Atlas and Giam, 1981). 



Phthalic acid esters are present in rather high concen- 

 trations at Enewetak. These compounds are widely used as 

 plasticizers. The concentrations are similar in air over the 

 Atlantic Ocean, the Gulf of Mexico, and in a rural area in 



TABLE 14 



Concentration of Synthetic Organic Compounds 

 in the Air and in Rain at Enewetak' 



'From Atlas and Giam, 1981. 



