NUCLEI OF ATMOSPHERIC CONDENSATION 
cause of the crisis in the iodine 
industries). 
Mechanical Sources of Nuclei 
In contrast to the particles treated in the foregoing 
section, which grow from molecular dimensions, the 
dust particles and the droplets of sea spray are produced 
by mechanical separation. Simpson [36] points out that, 
according to Gibbs, the limit of these separations is of 
the order of r = 5 X 107° em as a result of the action 
of cohesion- and surface-forces; usually, however, the 
particles are found to be substantially greater. Thus 
Kohler [21] found in his spray experiments with sea 
water that the greatest number of droplets had dimen- 
sions ranging between r = 1.5 and 3.5 X 10~ cm, that 
is, the same size as the haze droplets obtained by Des- 
sens. 
As a result of the thorough investigations by Wood- 
eock and Gifford [43] it appears certain that over the 
ocean the large nuclei largely consist of sea water 
sprayed by storms and surf and are transported by 
austausch to great heights in maritime air masses. The 
chloride content of hoarfrost and precipitation [47], the 
observed cubic crystals sublimated from haze droplets 
over the continent [1, 8], and the observation by Cauer 
[4, 6] of considerable traces of Mg and Cl ions during 
influx of maritime air masses into the Tatra mountains 
lead to the conclusion that, far into the continents, the 
haze droplets among the large nuclei represent a more 
or less significant portion of maritime aerosol. Although 
it is certain that these nuclei are often numerically 
insignificant as compared to the nuclei concentrations 
over densely populated continents, they nevertheless 
play a role in the analysis of traces of substances be- 
cause of their size. 
It is still uncertain to what extent the Aitken-nuclei 
over the oceans consist also of seawater spray [11, 37, 
46, 47, 48]; it is certain only that the oceans are not 
very productive sources of nuclei in point of numbers 
[3, 23] (Table I), so that the numerical proportion of 
NaCl-Aitken-nuclei is probably small over land. 
One important source of nuclei is the particles that, 
together with dust, are raised by storms over land. 
Substantial amounts of matter can thus be carried 
considerable distances, as is indicated by the Sahara- 
dust falls occasionally observed in Europe [12]. 
Tn conclusion of the discussion on the sources of at- 
mospheric nuclei, the estimates of the relative contribu- 
tions by various sources to the total nuclei content of 
the air, first given by Lettau [24], may be reproduced. 
If the total production of the nuclei is set to equal unity, 
the proportions indicated below are obtained, attribut- 
able as follows: 
Steppe and forest fires.............ccceeee eevee 0.4 
Detachment from the soil surface.............. 0.3 
Combustion products from man-made fires..... 0.2 
Molcanicricuiviuyeen ee ene ene nee 0.1 
Detachment from the sea surface and from extra- 
HELLEStTI All |SOUNCES yshiuc.s.ois. olen sioreye are avers oenlereeee negligible 
amounts 
The indicated values can be taken only as very rough 
approximations. 
187 
Electrostatic Charges of Nuclei 
The electrical state of an aerosol is conveniently 
characterized by the ratio 
a.) total number of nuclei 
sum of positive and negative ions” 
The combination of small ions and uncharged nuclei, 
which is, among other things, considered as proportional 
to the surface area of the nuclei, is increased in the case 
of charged nuclei as a result of the attraction of the 
electric charges which is independent of the size of the 
nuclei. It follows that a greater percentage of the larger 
nuclei must be charged. Wright [45] derived the values 
TasLEe III. RELATIONSHIP BETWEEN P AND THE SIZE OF 
Nucuer (after Wright [45]) 
Radius of nucleus 
(Gin, X< 10-8)... -d06 1.0; 2.0} 4.0} 6.0] © 
1.7 
© 10.0} 3.3] 2.0 1.5 
given in Table III. The quantity P can be measured 
by the following two methods: 
1. Through the determination of the total nuclei 
count and the nuclei count after the elimination of the 
large ions (both found with a nuclei counter). 
2. Through the determination of the total nuclei 
count and of the number of elementary charges (with 
an ion counter). 
From the difference of the two measurements [14, 15], 
we obtain the number of multiple charges on the nuclei 
5 x 10% 
NUMBER OF NUCLEI CM~3 
Fic. 4—Percentage of doubly charged ions as a function of the 
number of nuclei [14, 15]. 
(Fig. 4). With nuclei counts below 5000 cm-* a con- 
siderable proportion of nuclei are doubly charged. 
From extensive observations by Israél [16] and others 
the following relationships involving P are obtained: 
1. There is an increase of P with increasing nuclei 
count, varying locally; this increase becomes more pro- 
