NUCLEI OF ATMOSPHERIC CONDENSATION 
permits the measurement of the size distribution of 
these particles. However, such an “ion spectrum” is 
not equivalent to the ‘nuclei spectrum,” because: 
1. The proportion of nuclei with an electrical charge 
depends upon their size. 
2. Ions have multiple charges when the number of 
nuclei is small and their size large (see pp. 187 f.). 
It is therefore not permissible to infer the number of 
particles from the number of electrical unit charges. 
Figure 1 gives examples of such ion spectra with the 
terminology introduced by Israél. The influence of a 
183 
counter is correctly computed from the expansion [17]. 
Observations of the fall velocity of the nuclei [23] as 
well as of the optical properties of haze [35, 46, 48] 
establish only mean nuclei sizes. Photographs taken 
with the electron microscope appear to be most promis- 
ing. Here, however, it must be considered that during 
the exposure all the water and, to some extent, also the 
solid substances evaporate because of the high vacuum 
in the microscope and the heat generated by the elec- 
tron beam. For this reason, the residues that are photo- 
graphed represent only minimal sizes. 
5 io 2 5 10° 
eee |e | LI 
42 26 15 67 24 12 
14 9 6 2.5 lo} 0.4 
Eee 
ies 
—=— SMALL 
MEDIUM =10NS MEDIUM-IONS IONS 
ULTRA LARGE 
ONS = 
AITKEN= NUCLEI! (LARGE IONS. 
SOLID:SOLID AITKEN-NUCLEI 
LIQUID: NUCLE! DROPLETS 
6 
LARGE NUCLEI 
DUST PARTICLES i 
HAZE DROPLETS 
10-4 
RADIUS IN CM ——> 
2 5 107 2 5 1075 2 5 
Lf LISI oT LTE ET 
rN 
Fie. 1—A survey of the size range of atmospheric condensation nuclei. 
. Notation used in the text for the various types of nuclei. 
. Classification of ions according to Israél [18]. 
. Size range of newly formed gas-flame ions [19]. 
OMIM wher 
. Size distribution of atmospheric dust [10]. 
. Distribution of the ions in per cent of the total as found in Bad Gastein [18]. 
. Distribution of the ions in per cent of the total as found in Frankfort-on-the-Main [18]. 
. Size range of the Aitken-nuclei according to photographs taken with an electron microscope [26]. 
. Size range of soot, crystals of cigarette smoke, etc., according to photographs taken with an electron microscope [41]. 
. Per cent distribution of haze droplets as found by Dessens [8]. 
. Predominant sizes of the dust particles in winter (W) and summer (S) [88]. 
11. Size of haze droplets (H) and dust particles (D) of preferential optical effectiveness, according to Siedentopf [35]. 
per cent relative humidity. 
large city is clearly shown by the high content of large 
ions. The upper limit of resolution of the ion spectra is 
at r + 10° cm. 
There have been other attempts to determine the 
size distribution of nuclei. For example, by measuring 
the supersaturation necessary for condensation [19], it 
is possible to infer the “size spectrum of the nuclei” 
from the “supersaturation spectrum,” under the as- 
sumption that, as with droplets of solution, there is an 
unequivocal relationship between nuclei size and super- 
saturation and that the supersaturation in the nuclei 
. Supersaturation values necessary for the condensation on pure water droplets (above) and droplets of solutions (below) in 
The range of particles up to about r = 2 X 107° cm 
may be designated here as Aztken-nuclez. For the time 
being there is no method available for determining the 
proportion of nuclei droplets and solid nuclei in this 
size range. However, from the growth of these particles 
with increasing humidity (see pp. 184 f.) we may infer 
that there is a preponderance of nuclei droplets. 
For reports on the results of nuclei counts we may 
refer to the excellent monographs by Landsberg [23] 
and Burckhardt and Flohn [8]. The nuclei concentra- 
tions vary within a wide range; absence of nuclei, how- 
