CHAPTER SPECIAL OBSERVATIONS A series of special gummed film collections were made on Ponape, in the Caroline Islands, In addition to the regular gummed film observations, (which were made at 0030 GCT daily at Ponape), a gummed film stand was volaced near the windward shore of the island to attempt to sample air unaffected by local dust sources, No significant differences were found. Another gummed film stand was placed near the regular stands, but the film was changed at 12-hour intervals, in the morning and evening. On 11 days with reavy fallout, the film exposed during the daytime hours collected about 50% more activity than did the film exposed during the night hours, despite the fact that precipitation was about equally distributed in the two periods. This my be a result of the nocturnal stabilization of the very lowest layers of the atmosphere which inhibited the deposition of debris from turbulent eddies, although diurnal variations in the vertical temperature lapse rate are small on a 13l-square-mile island in the trade wind belt. To investigate the depositionof debris due te rainfall, Tainwatgr samples were collected by a 3C-inch diameter funnel (4.9 £t°) coincident with the exoosure of the 2h-how films. The collected water was filtered at the end of each observation period and the filter sent to New York, for analysis. On the nine days with the heaviest fallout at Ponape, the total collection on the rain filters averaged 56% as much activity as on the one-sqwre-foot gummed film. During the month of June, when fallout was relatively light, the rain filters collected twice as much activity as the gummed film, This is again indicative of the importance of the rainout process in bringing old debris (and presumably smaller particles) to the ground, - 36 -