The Influence of Climate and Weather Elements on the 
Activity of Natural Freezing Nuclei 
Hans-WALTER GEORGIL 
Department of Meteorology and Geophysics, University of Frankfurt, 
Frankfurt, Germany 
Abstract—The paper presents results of parallel measurements of freezing nuclei and 
condensation nuclei. The results gained at different places on the European continent 
in different altitudes and under purely maritime conditions are compared. They clearly 
show the effect of various weather conditions and the influence of certain trace sub- 
stances in the ground layer of the atmosphere on the freezing-activity of the aerosol 
particles. 
Introduction—During the past years simul- 
taneous investigations on condensation nuclei 
and ice nuclei were carried out by the author in 
order to gain a deeper understanding of the 
mechanism of heterogeneous phase transition in 
supercooled clouds. The experiments on conden- 
sation nuclei were performed on the basis of the 
results gained by Junge [1952] on the size distri- 
bution and the composition of the atmospheric 
aerosols. Our studies led to the detection of cer- 
tain relations between the freezing nuclei and the 
aerosol particles of certain size ranges. 
The present paper will deal mainly with three 
problems: 
(1) What is the difference between the results 
gained under different weather conditions and 
at places with different climatic conditions? 
(2) In what way does the altitude at which 
the measurements are performed influence the 
activity of the freezing nuclei? 
(3) How is the activity of natural freezing 
nuclei influenced by the presence of certain trace 
substances and pollutants? 
The freezing nucleus measurements were per- 
formed in an 865-liter mixing cloud chamber 
which was described in detail elsewhere [Georgii, 
1956]. The following places were chosen for the 
investigations: (a) at Frankfurt am Main as 
base station, (b) on the Taunus ridge in an al- 
titude of 800 m, 20 mi from Frankfurt (Taunus 
Observatory, Mt. Kleiner Feldberg), (c) on the 
summit of the Zugspitze at 3000 m altitude, and 
(d) on Valentia Island off the west coast of Ire- 
land as maritime station. On the Irish west coast 
westerly winds prevail supplying a constant rate 
of fresh maritime aerosol particles. 
Before dealing in more detail with the prob- 
lems mentioned above, some earlier results of 
our research will be briefly summarized. The 
concentration of freezing nuclei active within the 
temperature range 0°C to —30°C shows a di- 
urnal trend with a minimum in the early after- 
noon and a maximum during the night. This 
diurnal fluctuation runs parallel to that of the 
large condensation nuclei. It is most pronounced 
in summer and on days with calm sunny weather. 
The measurements taken on the Zugspitze show 
an inverse trend, namely, maximum in the after- 
noon, minimum during the night, indicating that 
the diurnal fluctuation of the numbers of ice 
nuclei is caused mainly by vertical convective 
mixing. 
The evaluation of the parallel measurements 
of freezing nuclei and condensation nuclei (the 
latter were measured in three size ranges sepa- 
rately, Aitken nuclei, ‘large’ nuclei, and ‘giant’ 
nuclei) revealed that there definitely exists a re- 
lation between the concentration of freezing nu- 
clei active above —30°C and the number of large 
condensation nuclei. This result was confirmed 
at all three continental stations and could be 
supported by direct methods, namely, by filtra- 
tion of particles of definite size from the air 
sample to be checked on ice nuclei. 
On the other hand it could be proved that the 
Aitken nuclei are ineffective as freezing nuclei 
above —80°C. A detailed description of these 
investigations is being published [Georgii, 1959]. 
Influence of weather elements—The evaluation 
of the daily measurements showed a considerable 
fluctuation of the concentration of freezing nu- 
clei from day to day. The great number of counts 
made at Frankfurt permitted an analysis of the 
relation between the occurrence of certain 
weather phenomena at the time of the measure- 
ments and the concentration of freezing nuclei 
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