-20- SUMMARY AND CONCLUSIONS ( Mass loading (all aerosols) on a HV filter was 55 ~g m-3 on Bikini Island over stabilized and vegetated surfaces (e.g., in a bare field following rain and in a coconut grove). This compares to 56 pg m ‘3 measured at a vegetated site on Engebi Island of Enewetak Atoll in February 1977, and a 42 vg m-3 weekly average for 10 weeks in a coconut grove on Eneu Island of Bikini Atoll May-August, 1978. (Wind speeds were comparable, 4-5 m s-], in all cases.) The more detailed studies at Bikini revealed that 34 ug m-3 of the mass loading was salt from sea spray, and that this sea spray contribution remained constant across Bikini Island beyond 20-50 m from the windward beach. ,, ,. .- The “background” concentrations of aerosol plutonium on Bikini are ~omparable to those on Engebi Island, Enewetak, when one considers the surface soil plutonium activity (Table 8). And, by assuming that Engebi Island had the same aerosol sea spray background (34 ug m-3) as Bikini (which has not been verified by actual measurement) we found that the enhancement factors agree ,, reasonably well. The normal enhancement factor is 0.56, if one assumes that values less than one (Table 8) represent normal variations about the mean of 0.56. Apparently, the process of resuspension is preferentially selective to non-contaminated particles on these atolls to the extent that an aerosol plutonium dilution of 1.8:1 normally occurs. TABLE 8. Location Plutonium Aerosol Concentrations (Winds 4-5 m s-l). Surface Description Bikini Coconut Grove Bikini Stabilized Bare Soil Engebi on Bikini and Enewetak Atolls Ccmpared Plutonium Aerosol Concentration (aCi m-3) ‘Vegetated Field 60 ( Surface Soil Plutonium Activity .(pCi q-l) Estimated Enhancement Factor* 8.01 0.41 264 15.3 0.82 240 24.2 0.45 15.3 3.10 Unusual Conditions Bikini Field, freshly tilled 6466 Engebi Garc!en, freshly tilled 7420 24.2 4.41 Engebi Garden, 1 wk after tilled 3060 24.2 2.55 Bikini Road with traffic 421 Engebi Downwind of road 1090 4.10 ,’ 35.2 ; 2.50 0.56 *Calculated by assuming 34 pg m-s sea spray which has been verified by measurement on Bikini. . c’-