PARTICLE SIZE DISTRIBUTION AT 110,000 FT
139
Table 2—SIZE-DISTRIBUTION RESULTS
Number of particles
diameter, p
‘Particle
2562, 2569, and 2572
Flights 2556,
Flight
< 0.0008
0.0009 to 0.0016
0.0017 to 0.0032
0.0033 to 0.0064
0.0065 to 0.0128
*
354
58
205
32
*
*
32
257
1998
*
*
*
5
7
*
9
10
2
4521
0.0129 to 0.0256
0.0257 to 0.0512
0.0513 to 0.102
0.103 to 0.205
0.206 to 0.409
46
g
4
2
0
139
366
62
17
27
51
1173
455
1376
716
2205
140
171
76
70
0
0
0
0
0
0
28
15
7
1
1
1
188
23
2
1
0
0
46
16
35
2
0
0
710
2951
3997
7303
0.410 to 0.819
0.820 to 1.64
1.65 to 3.28
3.29 to 6.75
6.76 to 13.5
13.6 to 27.0
Totals
2611
Flight
T-781-A
Flight
T-796-A
*The lack of data is the result of either an absence of particles in the
size group or microscope resolution limitations or both.
concentrations, the time of year, and the sampler performance was
not significant. However, changes produced by the weapons tests of
1961 and 1962 could have given rise to the observed variations in the
particle size distributions.
Further examination of the size-distribution results reveals differences in the lower cutoff points among the test groups. These differences may be the result of different minimum sizes in the stratoSphere at the time of collection, of variation in the resolution obtained
with the electron microscope, and of different particle-charging proba-
bilities.* These probabilities, which are related to ion densities and
particle residence times in the sampler, may have been affected by the
use of different flow rates and precipitator corona currents in the
tests.
Because of the limitations in the collection of particles by the
experimental sampler, in the evaluation of contamination, and in the
subsequent size determinations (which are reflected in the wide range
of median sizes reported), the results should be used only as indica-
tions of the true size distributions. Similarly, the calculated particle
concentration of 104 particles per cubic foot (3.5 x 107! particle per
cubic centimeter) should be regarded qualitatively.
*See paper by B. Y. H. Liu and K. T. Whitby, this volume.