INFLUENCE OF WEATHER ELEMENTS ON FREEZING NUCLEI 235 
80 and 84% of the annual average. The mean 
fluctuation of the individual values was also eal- 
culated and entered in Figure 2, showing that the 
quantitative interpretation is representative. 
The evaluations entered in Figures 1 and 2 in- 
dicate the effect of different weather factors on 
number and activity of freezing nuclei. It is 
now of interest to compare the Frankfurt analy- 
sis with those gained at the other locations. 
Influence of climatic elements on the concen- 
tration of freezing nuclei—As already mentioned 
in the introduction of this paper the investiga- 
tions were extended to three continental and one 
maritime location. A summarizing survey of the 
results is shown in Figure 3. The mean numbers 
of freezing nuclei, and large and Aitken nuclei 
at Frankfurt were set equal 100 and the average 
values of the measurements at the other loca- 
tions were related to the Frankfurt average. Fig- 
ure 3 presents an interesting result. Compared 
with the Frankfurt average the freezing nucleus 
concentration found at Mt. Kleimer Feldberg is 
63%, on the Zugspitze 80% and at Valentia Is- 
land 27%. Referring however to the very active 
freezing nuclei agitating ice nucleation above 
—20°C, the picture becomes still more amazing 
since the absolute concentration of these freezing 
nuclei is higher on Mt. Klemer Feldberg than at 
Frankfurt (125%). For Valentia Island we found 
65% and for the Zugspitze 44%. 
The distribution of the condensation nuclei 
shows a considerable deviation from these re- 
sults. For the large nuclei (r above 0.2 ».) the 
numbers found at Mt. Klemer Feldberg amount 
to only 18%, on the Zugspitze to only 4%, the 
corresponding values for the Aitken nuclei are 
9% and 4% of the Frankfurt concentration. With 
regard to Valentia Island large nuclei could only 
be measured during a short period of time and 
are therefore not included in the summary given 
in Figure 3. The number of Aitken nuclei was 
only 2% of the Frankfurt mean number. This 
low number of Aitken nuclei at a maritime site 
is in good agreement with the findings of other 
investigators. The concentration is of the same 
order of magnitude as given in the survey by 
Landsberg [1938] in which the results gained at 
21 different maritime locations are compiled and 
it Is In agreement with the assumption by Mason 
and Moore [1954] that all Aitken nuclei found 
over the oceans are of continental origin. A full 
account of the investigations on Valentia Island 
had been given by Georgii and Metnieks [1958]. 
The vertical decrease of the particle number 
140 
130 
120 
10 
100 
90 
80 7, 
70 
60 
50 
Relative number of freezing nuclei 
40 
30 
20 
Fie. 2—Annual summary of the evaluation of 
the weather effect on the freezing nucleus con- 
centration at Frankfurt am Main 
of the atmospheric aerosols as measured by us 
at the three continental stations at 100 mtrs, 800 
mtrs and 3000 m altitude corresponds closely to 
former investigations not only as far as the trend 
is concerned but also with respect to the absolute 
concentration. In this connection attention is di- 
rected to the investigations by Weickmann [1957] 
on Aitken nuclei or the investigations by Dreis- 
bach [1956] on the vertical distribution of large 
nuclei. During 1955 and 1956 Reiter [1955] con- 
ducted measurements of Aitken nuclei on the 
Zugspitze to supplement his air electric measure- 
ments and found values very close to our own 
results. 
While our investigations confirm the strong 
vertical decrease of condensation nuclei of all 
sizes they show also clearly that the number of 
freezing nuclei (particularly the most active) 
decreases much slower. This means that the 
properties responsible for the phase transition 
