AEROSOL SPECTROMETER AND ITS APPLICATION 181 
in the presence of 7, which latter retards sig- 
nificantly the hydration of the smaller particles 
(d; < 0.35 w) as indicated by the partial preser- 
vation of the distribution of the unaltered de- 
hydrated aerosol (Fig. 11a, 0-50-0°) while a 
second maximum at dy, ~ 0.6 wu is indicated. 
The curves of Figure 1lde indicate the effect 
of T on dehydrated nuclei which is predictably 
negligible as the rh in C,; remains virtually un- 
changed (Fig. lle). However, a small increase of 
(rh) in Cy, that is, adsorption on the nuclei, 
appears to increase coagulation rate (decrease of 
small particles and small increase of larger sizes) 
for 7'-50-0°, similar to the effect of desorption 
from the nuclei in the absence of 7 in Fig. 11a. 
Figure 11f compares the dehydration of a hy- 
drated aerosol with 7 and without (7—50-24°). 
Obviously 7 increases sharply the number of 
smaller particles when contacting an increased 
humidity below the hydration level (rh), , con- 
trary to its effect on an already dehydrated 
aerosol (7-50-0°). These preliminary 
leave but little doubt about the marked in- 
fluence of organic traces in nuclear condensa- 
results 
tion phenomena. A detailed interpretation of 
these findings, in spite of their fair reproducibil- 
ity, appears premature and will be postponed 
until more detailed data are available. 
ConcLusIon 
The size-distribution spectra of natural and 
artificial aerosols in the submicron range appear 
realistic because the process of separation should 
interfere less with the airborne habitude of the 
particle than that of most methods available in 
the past. Moreover, the method permits discrim- 
ination between hydrated and dehydrated NaCl 
particles, because of the relation of the Stokes’ 
diameters, independent from the state of the 
nuclei after precipitation. The size-distribution 
spectra can thus be used to determine changes 
occuring among airborne nuclei by interaction 
with their gaseous environment, such as adsorp- 
tion or desorption, hydration and dehydration. 
It appears that, whenever such changes occur, 
the coagulation rate of the particles is affected 
and that organic traces in general delay these 
processes, possibly in analogy to the well-known 
‘nhibition’ of freezing nuclei [Birstein, 1957; 
Poppoff and Sharp, 1959]. 
This hypothesis satisfies also the pattern of the 
marine aerosol spectra. They show two maxima 
ds, dy, whenever a source of their generation, 
such as foam on wave crests [Blanchard and 
Woodcock, 1957], was within a few miles from 
the sampling site, most distinctly in the vicinity 
of sources of organic matter (kelp beds). At sub- 
stantially larger distance from such aerosol 
sources, the marine as well as the mountain 
aerosol spectra showed one maximum only. Nat- 
ural aerosols are probably rarely, if ever, free 
from organic traces, hence the persistence of 
hydrated fractions of the nuclei present under 
conditions of decreasing humidity could well be 
caused by such temporary protection against 
dehydration and vice versa. One has to realize 
that, contrary to such dispersions in the labora- 
tory, these aerosols represent mixtures of particles 
airborne for largely differing time intervals avail- 
able to them for attaining equilibrium states 
prior to precipitation in the A.S. 
Independent of the validity of the above in- 
terpretation the aerosol spectra, so far available, 
seem to definitely indicate the significance of 
gaseous organic traces in the atmosphere with 
regard to the rate of nuclear condensation, that 
is, to the formation of fogs and hazes as well as 
to certain phases of air pollution. It thus appears 
that a systematic research effort which combines 
size distribution studies of natural aerosols with 
their well defined synthetic replicas in the labora- 
tory promises a new chapter in the understanding 
of our immediate atmospheric environment. 
Acknowledgments—The work presented is part 
of a general investigation program on the Syner- 
gistic Properties of Aerosols supported by Re- 
search Grant (No. RG-6743) from the National 
Institutes of Health, U.S. Public Health Service. 
The authors wish to express their appreciation 
to the Instrument Development and Manufactur- 
ing Co., Pasadena, for putting an aerosol spec- 
trometer at their permanent disposal; also to 
Aerometric Research, Inc., Santa Barbara (R. E. 
Kerr, Jr. and E. Hovind) for contributing the 
wind-trajectory maps for the times and localities 
of the off-shore sampling sites. Furthermore they 
wish to give full credit to members of the re- 
search staff: to M. L. Warrick, Jr., for applying 
his mechanical skill to the construction of the 
micro-analyzer and to numerous other items of 
special equipment; to A. F. H. Goetz for his 
capable and conscientious assistance in the field 
and laboratory, particularly in the analy 
the aerosol spectra; and to Mrs. L. Hauck for 
her untiring clerical collaboration. 
sis of 
