246 
and —30°C) the freezing nucleus concentration 
in Valentia Island, Ireland, increased only very 
slowly, while at the three continental places a 
very sharp increase was observed. We assume 
that in the very clean maritime air around Val- 
entia Island an inactivation of the aerosol parti- 
cles by adsorbed trace substances does not occur 
while in Germany this is more or less everywhere 
DISCUSSION 
the case because of the overall effect of air pollu- 
tion. We are therefore also inclined to suggest 
that the relatively low concentrations of freezing 
nuclei which Kline observed in air masses com- 
ing from the interior of the country are also 
caused by a partial inactivation of the particles 
by pollutants which is not the case when the air 
is coming from the ocean. 
