RADIOACTIVITY OF THE ATMOSPHERE 
termining the balance (we restrict our examination 
to Rn). 
In the mean, the supply from the ground has to 
maintain an equilibrium with the rate of disintegration 
of An in the entire atmosphere. Let us disregard the 
variations in a horizontal direction and consider a 
vertical column of air of one square centimeter cross 
section reaching to the top of the atmosphere; the 
following equation must then be fulfilled: 
SA = #, 
where S is the entire Rn content of the column, ) is the 
disintegration constant of Rn, and £ is the exhalation. 
The total content S of the air column can be computed 
as 
es | s(h) dh, 
where s(h) represents the vertical distribution of Rn. 
For this function s(h) we may write the following 
differential equation: 
ds , dAds 
Te? a ah Oe 
in which p expresses the density of the air and A the 
austausch coefficient. 
Integrations of this equation have been carried out 
by Hess and Schmidt [25] for an austausch that is 
constant with height (dA/dh = 0), and by Schmidt 
[51] with corrections by Priebsch [46], and by Lettau 
[87] for various assumed values of an austausch coeffi- 
cient variable with height. Values for S and E# as caleu- 
lated by these various authors are presented in Table 
VI. The agreement between these values and the ob- 
TasiE VI. Toran RapON CONTENT AND RATE OF DISINTEGRA- 
TION OF A VERTICAL COLUMN OF UNIT Cross SECTION AND 
or ArmospHERIC HEIGHT, AFTER VARIouS AUTHORS 
Author (cx 10-12) (C sect 3¢ 10-3) 
Hess and Schmidt [25] 
Ami mOOnCNCIOe SECHL. |. a5... 13 27 
Ata O0 Note mim Seeley se 18 38 
Schmidt [51] 
@rrebsch y[46))). . .- yo. os nee cane 8 20 
Lente, [BZA dee Bea ee tees eee eee 27 57 
served exhalation of 40 x 10-8 C em- sec (Table V) 
can be considered entirely satisfactory. In summary it 
can be said that the emanation content of the atmos- 
phere over land and water can be completely understood 
if one considers the solid earth’s crust as the almost 
exclusive source of emanation. 
Problems 
Our knowledge of radioactive substances in the atmos- 
phere is fairly complete as far as their identity, meas- 
urability, and origin are concerned. Less clear is the 
mechanism of the horizontal and vertical distribution 
of these substances in the atmosphere. As admixtures to 
the air, they take part in its movement and thus 
159 
enable us to reach important conclusions regarding air- 
mass displacements. Therefore, if one considers the 
question of a suitable continuation of research, the 
use of radioactive air admixtures as tracers for special 
meteorological problems opens new possibilities. One 
experiment in particular suggests itself: the use of 
radioactive emanations as an indicator of austausch 
movements on the one hand, and for the determination 
of the life history of air masses on the other hand. 
Several of the above-mentioned investigations point 
in this direction; only a few will be mentioned. 
1. The vertical distribution of the imdividual radio- 
active component can be considered as the result of 
austausch [9, 25, 27, 37, 39, 46, 47, 51]; therefore, with 
proper measurements, it ought to yield, in turn, in- 
formation about its efficacy and vertical extent on the 
average as well as in single cases. 
2. Air that stagnates in the same climatic region for 
some time acquires, by contact with the ground, cer- 
tain characteristics which allow us to define it as an 
air mass of a given type. One must expect that the air 
mass also adopts different radioactive properties, ac- 
cording to the exhalation of the ground beneath. Thus, 
for mstance, an air mass located over the ocean for a 
long time, will show a considerably smaller Rn content 
than air from the continent, as has been shown by 
measurements of the author on the Dutch coast [80] 
(see Table IV). Furthermore, the pronounced activity 
differences which Becker [9] has found above and below 
an inversion point to the effects of austausch or air- 
mass characteristics. 
3. The radioactivity of precipitation gives an in- 
dication of the radioactive character of the air mass 
from which it falls. The pronounced increase in ioniza- 
tion near the ground during thundershowers [15, 57] is 
probably due to an especially strong upward transport 
of low-level (and therefore more strongly radioactive) 
air in the formation of a thunderstorm and the return 
of the radioactive admixtures through precipitation. 
Tt is obvious that a more thorough investigation of 
these relationships from a meteorological and thus at- 
mospheric-electrical and bioclimatological point of view 
can become of great importance. 
The methodological problems, for example, consist of 
the following: 
1. The over-all substitution of measurement by auto- 
matic recording. 
2. A simultaneous survey of diurnal variations of the 
radioactive elements in the air at several stations at 
various altitudes. 
3. Attempts at an air-mass classification according 
to origin and age on the basis of the Rn content and the 
proportion of Ra- to Th-derivatives. 
4, Vertical cross sections of the atmospheric radio- 
activity, perhaps by means of airplane measurements 
or by testing the active deposits on the mooring cable 
of a captive balloon when bringing it in (using Geiger 
counters). 
5. Determination of the radioactivity of precipita- 
tion. 
