CHAPTER

SPECIAL OBSERVATIONS
A series of special gummed film collections were made on.

Ponape, in the Caroline Islands. In additio to the regular gummed
film observations, (which were made at 0030 GCT daily at Ponape),
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 exnosed during the daytime hours collected .
about 50% more activity than did the film exnosed during the night
hours, desnite the fact that oreciritation was about equally

distributed in the two ceriods. This may be a result of the
nocturnal stabilization of the very lowest layers of the atmosovhere

which inhibited the decosition of debris from turbulent eddies,
although diurnal variations in the vertical termerature lapse rate

are small or a 13h-square-mile island in the trade wind belt.

To investigate the denosition of debris due tc rainfall,
va inwa tgr samples were collected by a 30-inch diameter funnel

(4.9 £t°) coincident with the exoosure of the 2h-hour films.

The

collected water was filtered at the end of each observation neriod

and the filter sent to New York, for analysis.

Cn the nine days

with the heaviest fallout at ronape, the total collection on the

rain filters averaged 56% as muchactivity 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 nreswably smaller

particles) tc the ground.

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