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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