CHAPTER } SPECIAL OBSERVATIONS A series of special gummed film collections were made on Ponape, in the Caroline Islands. In additim to the regular gummed film observations, (which were made at 0030 GCT daily at Poriape), a gummed film stand was vlaced 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 heavy 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 dimnal variations in the vertical temperature lapse rate E are small on a 13h-square-mile island in the trade wind belt. (4.9 £t*) coincident with the exoosure of the 2h-hour 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 roa To investigate the devosition of debris due te rainfall, rainwater samles were collected by a 30-inch diameter funnel rain filters averaged 56% as much activity as on the one-squire-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 wey wa rainout process in bringing old debris (and presumably smaller particles) to the ground. - 38 -