Environmental Engineering Reference
In-Depth Information
N
D
2.69
10
19
cm
3
corresponds to the
temperature
Ta b l e 6 . 10
The mobilities of some neg-
ative and positive ions in nitrogen [155-
158]. The mobility
T
D
273 K and a pressure of
1 atm) and is expressed in square centimeters
per volt per second.
is reduced to normal
conditions (the nitro
gen number density
K
Ion
K
NO
2
2.5
NO
3
2.3
CO
3
2.4
NO
2
H
2
O .4
NO
3
H
2
O .2
CO
3
H
2
O2.1
N
2
1.9
CO
2
2.2
N
2
H
C
2.1
N
3
2.3
N
2
O
C
2.3
N
4
2.3
H
C
H
2
O2.8
H
C
(H
2
O)
2
2.3
H
C
(H
2
O)
3
2.1
300 cm
3
and over the ocean we have
N
i
500 cm
3
.
number density of
N
i
D
D
Note that molecular ions carry only a part of the atmospheric charge.
Let us consider the ionization balance in the lower atmosphere. There are two
mechanisms for the ionization process. Near the Earth they result from radioac-
tivity of the Earth's surface, but these processes proceed in a thick layer. Another
mechanism is determined by galactic and solar cosmic rays [159-161]. Maximum
ionization is observed at altitudes between 11 and 15 km, and is characterized by
ionization rates of [161] 30
40 cm
3
s
1
. This leads to an ion number density of
10
3
cm
3
if we use the recombination coefficient of about 10
6
cm
3
/s at
this altitude. This number density exceeds that at low atmosphere altitudes.
Thus, one can compose the following character of electric processes for the Earth
that is negatively charged owing to the falling of water drops in clouds. The charge
transfer from lower cloud edges to the Earth's surface results from electric break-
down in the atmosphere that is realized by lightning.
about 6
6.5.2
Lightning
Let us consider the characteristics of lightning as an atmospheric phenomenon.
Lightning is a powerful electric breakdown between a cloud and the Earth's surface,
between two clouds, or within one cloud. The length of the lightning channel is
measured in kilometers. Lightning is the most widespread electric phenomenon
