6 COMPOSITION OF THE ATMOSPHERE 
atmospheric methane and found it to coincide with that 
of biological methane. The analysis also places an upper 
limit of about 200 years on the mean lifetime of the 
methane in the atmosphere and suggests an annual 
production of upwards of 10’ tons of methane from 
biological sources. 
Hydrogen (H2). The H, content of air is known 
only approximately. Paneth [16] concludes that it is a 
constant constituent of atmospheric air and that its 
amount can be assumed to be about 5 X 1077 by vol- 
ume. Recent analyses by the author and G. P. Kitt gave 
varying amounts of H». upwards of 0.4 ppm, and in- 
vestigations are in progress to see whether these varia- 
tions occur in the free air or are due to local contam- 
ination. 
Summary. The figures believed to be most reliable 
for the constituents of dry air are listed in Table V. 
Tasie V. NoNVARIABLE CoMPONENTS OF ATMOSPHERIC AIR 
Constituent Content (per cent) Content (ppm) 
IN otf A Stores Se re ae 78.084 + 0.004 
(OF tc eet otecnase he tie oor: 20.946 + 0.002 
(COPE: et wien aah oie: 0.033 + 0.001 
TA BESS eibacr «Mn Ooh Reece 0.934 + 0.001 
IN G2rs ahiheerunct cede ots 18.18 + 0.04 
15 (peter np ree 5.24 + 0.004 
ETRE varie SMe Me AR 1.14 + 0.01 
ORE Pasar Hon rae abs 0.087 + 0.001 
Yc Ceara BRASS ERcen eee ea 0.5 
(OE Mioie Gebers ae ole oe 2 
IN SO) ees ei ees 0.5 +0.1 
* Extrapolated to 1950 according to Fig. 1. 
CONSTITUENTS OF VARIABLE 
CONCENTRATIONS 
(Excluding Water Vapour) 
A rough survey of some of these constituents is 
given in Table VI. 
TaBLeE VI. VARIABLE CONSTITUENTS OF DRY 
ATMOSPHERIC AIR 
Constituent Ori gin Proportion in ground air (range) 
OR eee Ultraviolet radia- {0 to 0.07 ppm (summer) 
tion 0 to 0.02 ppm (winter) 
Owen ae Industrial 0 to 1 ppm 
INO. ac0000% Industrial 0 to 0.02 ppm 
QS), 05000% Biological or oxy- | Uncertain 
dation of CH, 
Toe ah x28 hoe: Industrial Up to 10% g m= 
INCH 3 0 08 2 Sea spray Order of 10-4 g m= 
INIET Sey eee Industrial 0 to trace 
CORFE ose Industrial 0 to trace 
Ozone (O;). The bulk of atmospheric 03 is con- 
tained in the stratosphere, where it is produced by the 
ultraviolet radiation from the sun. The problems con- 
nected with its production and occurrence there form 
the subject of a separate article in this Compendium.® 
We shall deal here only with observations of O3 near 
the surface. 
3. Consult “Ozone in the Atmosphere” by F. W. P. Gotz, 
pp. 275-291. 
Methods of Determination. The main difficulty in the 
determination of O; in atmospheric air lies in the fact 
that simple chemical reactions are not specific for O3 
and that gases like H.02, NO2, and SO: interfere with 
the chemical determination, the first two by increasing, 
the last by decreasing the analytical result. However, 
these gases occur only in the vicinity of human habi- 
tation. On the other hand, the spectroscopic investiga- 
tion of surface air [7, 13], though accurate, is so time- 
consuming (due to the necessary photometry of the 
spectrograms) that it does not lend itself to routine 
observations. This also applies to the chemical method 
of Edgar and Paneth [e. 12] which relies on the separa- 
tion of O3 from all other gases by low-temperature 
adsorption on silica gel. However, two accurate methods 
have been evolved which give reliable results in a 
comparatively short time and thus make possible large 
numbers of determinations under quickly changing me- 
teorological conditions. (See V. H. Regener [c. 17] and 
Glueckauf, Heal, Martin, and Paneth [c. 12].) 
The results obtained so far can generally be explained 
on the basis that Oz; which is produced in the higher 
regions—mostly in the stratosphere and possibly some 
just below the tropopause—reaches the ground level 
through the turbulence of the air, and on its way down 
is gradually diminished and eventually destroyed by 
oxidisable materials of an organic and inorganic char- 
acter. 
Diurnal Variations. On days with little turbulence, 
the ground O; found during the day usually disappears 
at nightfall because of the increased stability of the air, 
but it remains unaffected at higher wind velocities. 
Annual Variations. Pronounced maxima (7 X 10-8 
by volume about May) and minima (2 X 107° about 
November) of the ground O; have been found by many 
observers. The fact that these annual variations are 
greater than those of the total O; may be due to the 
greater instability of the atmosphere during the sum- 
mer months. There are some indications that at higher 
latitudes (e.g., Abisko, Lapland) the high summer 
values of ground O; appear later, if at all. 
Geographic Variations. Next to nothing is known 
about the geographical distribution of O; over conti- 
nents and oceans. Almost all determinations have been 
carried out between the latitudes 45°N to 68°N over 
land. Usher and Rao [22], however, reported the ab- 
sence of ground O3; in India. This result may not be 
reliable, but there is obviously wide scope for further 
investigations. 
Ozone during Depressions. The usually high wind 
velocity and atmospheric turbulence during depressions 
result in high O3 contents (subject to the seasonal 
variations). However, low values of O3 were found 
at Durham, England [10], even at high wind velocities 
in advance of warm fronts, and during occlusions of 
the cold-front type. Apparently under these conditions 
inversions are formed which restrict the turbulent inter- 
change of air masses near the ground with the O; 
produced in higher regions. It is to be expected that 
such phenomena will be greatly reduced in regions 
with low industrial contamination (e.g., over the 
