82 



MERRILL AND DUCE 



ogy, University of Hawaii. They are tabulated as hourly 

 totals of the shortwave radiant energy flux, in cal cm 

 h~^ Because the data coverage is not continuous (no 

 period longer than 8 months is available without extended 

 interruption), it is not presented here. 



Many useful and interesting data were collected by 

 Blumcnstock and Rex (1960) in addition to those discussed 

 previously. 



ATMOSPHERIC CHEMISTRY OF 

 ENEWETAK ATOLL 



Introduction 



During the period April to August 1979, an extensive 

 program investigating the chemistry of atmospheric trace 

 gases, particles, precipitation, and dry deposition was 

 undertaken at Enewetak Atoll. The Sea/ Air Exchange Pro- 

 gram, or SEAREX, was sponsored by the National Science 

 Foundation and involved efforts by 11 institutions from the 

 United States, France, and Great Britain. The impetus for 

 this atmospheric chemistry study was the increasing 

 interest in the possibility that significant quantities of both 

 natural and anthropogenic substances may be transported 

 to the ocean via the atmosphere in mid-ocean regions. An 

 understanding of the importance of the atmosphere as a 

 transport path is critical in determining the basic geochemi- 

 cal cycles and budgets of a variety of naturally occurring 

 substances and in predicting the near-global impact of 

 anthropogenic material in open ocean regions. The objec- 

 tives of the study were to investigate the concentrations 

 and sources of selected inorganic and organic substances in 

 the marine atmosphere at Enewetak, their flux into the 

 ocean, and the mechanisms of their exchange with the 

 ocean. Substances investigated included trace metals such 

 as lead, cadmium, zinc, selenium, copf)er, iron, antimony, 

 manganese, mercury, silver, aluminum, and the alkali and 

 alkaline earth metals; soil dust; atmospheric sea salt; ^'"^b 

 and its daughter ^'°Po; particulate organic carbon; and 

 organic compounds such as PCBs, DDT, aliphatic hydro- 

 carbons, phthalate plasticizers, fatty acids, fatty and poly- 

 cyclic alcohols, and low molecular weight ketones and 

 aldehydes. 



The atmospheric chemistry studies at Enewetak Atoll 

 took place on Bokandretok Island, just north of Enewetak 

 Island (Fig. 5). During late November and December 1978, 

 an 18-meter-high walk-up sampling tower and three small 

 buildings were constructed on Bokandretok. The sampling 

 tower, located directly on the east coast of the island, was 

 necessary to get above any local contamination from both 

 man-made sources and natural sources such as erosion 

 products and surf spray generated when waves strike the 

 shoreline. 



Additional precautions were taken against local con- 

 tamination. Sampling pumps were located on the ground 

 and were connected to the collection systems on top of the 

 tower by 20 meters of hose. The operation of the pumps 



N 



1 



^<f 



.BOKANDRETOK 



TOWER / 



site/ 



MID-PACIFIC 



RESEARCH 



LABORATORY 



Fig. 5 SEAREX tower site on Bokandretok Island, just 

 northeast of the Mid-Pacific Research Laboratory on 

 Enewetak. 



was controlled automatically as a function of local wind 

 speed, direction, and total condensation nuclei in the 

 ambient air. Pumps were shut down when the wind direc- 

 tion could cause local contamination from Bokandretok or 

 other islands in the atoll, when the speed was less than 

 2.5 ms ', or when the condensation nucleus count was 

 greater than 300 to 400 cm"^, a typical background level 

 for marine air. The air sampling tower on Bokandretok is 

 shown in Fig. 6. 



The SEAREX experiments were scheduled to begin in 

 early January 1979. However, on Jan. 5, 1979, Typhoon 

 Alice struck Enewetak with winds over 50 ms and very 

 high tides. The SEAREX tower and one building on 

 Bokandretok survived but with some damage. The remain- 

 ing buildings and the submarine cable supplying power to 

 Bokandretok were destroyed. The experiments were 

 delayed until repairs could be made, and sampling began in 

 April 1979. 



Atmospheric Sea Salt 



The ocean is the largest source for particles, on a mass 

 basis, in the global atmosphere. These sea salt particles 

 are produced when wave-produced bubbles burst at the 

 ocean surface (Woodcock, 1953; Blanchard, 1963). Con- 

 centrations of this sea salt arc extremely high immediately 

 downwind of surf breaking on a reef or a shoreline. In 

 these areas, atmospheric sea salt concentrations can easily 



