180 
upon the condensation process.) The residence 
times, 7: = 80 sec and rT. = 5 sec, were chosen, 
while the nebulizer temperature was either Ty = 
0° C to obtain a dehydrated, or Ty = 24° C fora 
hydrated NaClaerosol in C; . The NaCl concen- 
tration in NV was 3.6% (0.615 n), for similarity to 
seawater (Pacific). The organic material in these 
tests was turpentine as representative of the type 
of compound yielded by plants into the atmos- 
phere [Vonnegut and others, 1957], also pinene 
and n-butanol have been used with similar effects. 
Control tests conducted with double distilled 
H.O in the nebulizer showed, even after extended 
exposure, no traceable deposit in the A.S. and 
thus proved that the combination of water and 
organic vapor does not produce an aerosol by 
itself. 
The operating conditions of the A.S. were 
identical for all spectra in Figure 11 and the same 
as for the natural aerosols in Figure 9Yabd, N = 
18,000, O = 1 and embracing a range of 3 uw > 
6 > 0.17 w. Carefully cleaned (xylene), polished 
chromium foils were used exclusively. Since the 
aerosol concentration was several hundred times 
larger than that encountered in nature the micro- 
photometric analysis could be used although the 
exposure time was but one to two minutes. 
The short residence in Cz is the apparent reason 
for a certain instability of the size distribution 
during the brief sampling period. To compensate 
for these, each time two spectra were taken under 
identical conditions and analyzed for the same 
32 L values, and then differentiated by deter- 
mining (AS) over intervals of Ad = 0.025 uw. The 
mean of each pair of AS/Ad was then plotted 
versus d. Adjacent points of this derivative curve 
were averaged again to minimize the unavoidable 
inaccuracies of this semi-graphical procedure. 
The systematic displacement of the 6-value so 
caused is (6 = 0.0125 wu) and was considered 
negligible for this type of experiment. 
Each size distribution curve in Figure 11 is 
thus based on 74 original S determinations and 
31 points derived from them. Figure 11a pre- 
sents four spectra of a dehydrated aerosol Ty = 
0° C after contact 72 = 5 sec with an air stream 
of a relative humidity varying between 14 and 
80%. The size distribution, typical for the nebu- 
lizer under the particular operating conditions 
used, is closely similar to those found in nature 
(Fig. 9) though for a maximum at a higher value 
(0.30 p > ds > 0.27 p). 
At a relative humidity of about 50% the hu- 
midity is slightly larger than in C,, hence any 
GOETZ AND PREINING 
effect on the aerosol, while in C2, is unlikely 
except for a possible small additional adsorption 
of moisture on the nuclei. The curve 0—50-0° 
shows a distinct maximum at 0.29 u > d, > 
0.25 w and a steady decline toward larger sizes. 
If the air flow is drier (0-33-0° and 0-14-0°) 
than in C; this maximum decreases with decreas- 
ing humidity in C2 concurrent with a slight fre- 
quency increase (as C'S’) for ds > 0.35 uw. This 
can be tentatively interpreted as an increased 
rate of coagulation of the (numerically very 
dense) small particles into fewer conglomerates of 
larger sizes, due to electric disturbances, caused 
by the desorption of residual moisture layers 
known to exist on dehydrated nuclei [Orr, and 
others, 1958b]. (It was assumed as a first approxi- 
mation that the original nuclei d; form conglom- 
erates of closest packed spheres d, , the number 
N required for forming a particle of the size 
d. is (w/6)(d,./ds)’. A decrease of, for instance, 
30% of original particles of d; would thus result 
in a 7% increase of conglomerates for d, = 2d; 
and only in 1.4% for d. = 3d, , ete.; qualitatively 
compatible with the experimental indication in 
Figure 11a.) 
The distribution is drastically altered when the 
relative humidity in C2 is larger than critical, 
that is, when the nuclei are being hydrated 
(O-80-0°). This causes a general shift to larger 
particle sizes. The interval 72, for contact with 
the moisture of the air stream is insufficient for 
the complete hydration of all nuclei, indicated 
by the partial remainder of the first maximum, 
similar to the type of marine aerosols in Figure 
9b. 
Figure 11b shows the effect of partial dehydra- 
tion of the hydrated aerosol (0-50-24°) by brief 
contact with an air stream of (rh ~ 50%) in 
comparison with the corresponding distribution 
curve (0-50-0°) in Figure lla. As is to be ex- 
pected, the dehydration, while far from being 
complete due to the short contact time, is suffi- 
cient to cause the shift of the maximum toward 
smaller 6 and the indication of a maximum re- 
maining at the 6 value of the hydrated aerosol. 
The variations of the distribution do thus essen- 
tially agree with the hydration pattern for hygro- 
scopic aerosols found by other authors previously 
for individual nuclei. 
The curves of Figure 11lcdef show the effect 
of organic traces T added in C2 with the air 
stream in comparison with the distribution in 
their absence. Figure 1le represents the hydra- 
tion pattern of a dehydrated aerosol (T—80-0°) 
