Geoscience Reference
In-Depth Information
Table B.1
Composition of atmospheric air up to 105 km altitude
Gas
Molecular mass
(kg kmol
-1
)
Volume fraction
(relative to dry air)
Nitrogen (N
2
)
28.013
78.08 %
Oxygen (O
2
)
32.000
20.95 %
Argon (Ar)
39.95
0.93 %
Water vapour (H
2
O)
18.02
0-5 %
Carbon dioxide (CO
2
)
44.01
389 ppmv
Neon (Ne)
20.18
18 ppmv
Helium (He)
4.00
5 ppmv
Methane (CH
4
)
16.04
1.87 ppmv
Krypton (Kr)
83.80
1 ppmv
Hydrogen (H
2
)
2.02
0.5 ppmv
Nitrous oxide (N
2
O)
56.03
0.32 ppmv
Ozone (O
3
)
48.00
0-0.1 ppmv
From Wallace and Hobbs (
2006
). CO
2
data: global mean value for 2010. Source:
data: Mace Head (Ireland) October 2009-September 2010. Source: AGAGE net-
work, Prinn
et al.
(
2000
).
With
M
d
.
, the speciic gas constant for dry air becomes
R
d
= 287
J kg
-1
K
-1
. Hence, using (
B.1
), the density of dry air can be deined as:
−
1
=
28 976
kg mol
M
R
p
T
p
RT
ρ
d
=
d
*
=
(B.4)
d
The speciic gas constant for water vapour is
R
v
= 462 J kg
-1
K
-1
. Based on Eq. (
B.3
)
the dependence of the molar mass of air that includes water vapour can be derived
to be:
−
1
q
1
28
−
q
=
M
+
(B.5)
18
.97
6
where
q
is the speciic humidity (deined in
Section B.4
). Hence the speciic gas con-
stant for moist air is:
*
R
M
q
1
28 976
−
q
=
(
)
*
R
=
=
R
+
R
d
1061
+
.
q
(B.6)
18
.
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