Environmental Engineering Reference
In-Depth Information
0.20
H
2
O, CO
2
0.16
300 K CFC
0.12
O
3
CH
4
275
250
225
0.08
N
2
O
H
2
O
0.04
200
175
0
0
200
400
600
1000
Wavenumber (cm
-1
)
800
1200 1400 1600 1800 2000
50
20
12.5
10
8
5
Wavelength (
m)
Figure 10.2
Earth spectrum (“earth-shine”) as observed from the Nimbus-7 satellite. Major absorption
bands by greenhouse gases are indicated. (Adapted from Liou, K. N. 1980.
Introduction to Atmospheric
Radiation.
New York: Academic Press.)
Reflected
(albedo) 103
Earthshine 240
Surface 40
Clouds 35
Sunshine 343
Greenhouse
gases 165
Atmospheric
molecules
Earth
Figure 10.3
Sun-earth-space radiative equilibrium. Of the incoming global annual solar radiation, about
30 % is reflected into space (albedo); the rest reaches the earth's surface or is scattered by clouds, aerosols,
and atmospheric molecules. Of the outgoing terrestrial thermal radiation, about 17 % goes directly into
space; the rest emerges after redistribution by clouds, aerosols, and greenhouse gases. Units are W m
−
2
.
earth, respectively.) About 30% of the incoming solar radiation is reflected into space by clouds
and the earth's surface. This factor is called the
albedo
. Another part (25%) is absorbed by gases
and aerosols, including clouds, in the earth's upper and lower atmosphere, exciting and splitting
molecules, and ionizing molecules and atoms (for example, solar UV radiation causes the formation
of ozone in the stratosphere and free electrons in the ionosphere). The rest (about 45%) reaches
and is absorbed by the earth's surface, thereby elevating land and water temperatures. Much of the
absorbed radiation goes into evaporating water from the oceans and other surface waters.
Quantitatively, the solar energy input to the earth on top of the atmosphere is
R
E
(
I
S
=
S
o
π
1
−
α)
(10.1)
