Environmental Engineering Reference
In-Depth Information
Ta b l e 6 . 6
Continued.
Type
Number
Typical process
Parameters
O
C
C
NO
C
C
10
13
cm
3
/s
Ion reactions
27
N
2
!
N
C
1.1 eV
k
D
6
O
2
O
C
C
10
11
cm
3
/s
28
O
2
!
C
O
C
1.5 eV
k
D
2
N
C
C
O
C
C
10
11
cm
3
/s
29
O
2
!
NO
C
2.3 eV
k
D
2
N
2
NO
C
C
10
10
cm
3
/s
30
C
O
!
N
C
3.2 eV
k
D
1
Σ
g
)
2O
2
(
1
O
2
(
1
10
17
cm
3
/s
Quenching
31
Δ
g
)
!
O
2
C
k
D
2
O
2
(
1
10
18
cm
3
/s
32
Δ
g
)
C
O
2
!
2O
2
k
D
2
Σ
g
)
O
2
(
1
10
17
cm
3
/s
C
N
2
!
O
2
C
k
D
33
N
2
2
N
2
(
A
3
Σ
C
)
10
12
cm
3
/s
C
O
2
!
N
2
C
k
D
34
O
2
4
O(
1
D
)
10
11
cm
3
/s
C
O
2
!
C
k
D
35
O
O
2
5
O(
1
D
)
10
11
cm
3
/s
36
C
N
2
!
O
C
N
2
k
D
6
O(
1
S
)
10
13
cm
3
/s
37
C
O
2
!
O
C
O
2
k
D
3
O(
1
S
)
10
12
cm
3
/s
38
C
O
!
O
C
O
k
D
7
10
14
cm
3
/s
Chemical reaction
39
O
C
O
3
!
2O
2
k
D
7
10
34
cm
6
/s
Three body
40
O
C
2O
2
!
O
3
C
O
2
K
D
7
10
34
cm
6
/s
association
41
O
C
O
2
C
N
2
!
O
3
C
N
2
K
D
6
a
Per atom, molecule, or ion for daytime atmosphere at zero zenith angle.
b
At a pressure of 1 atm.
formula (1.48)
0
@
1
A
,
Z
h
mgdz
T
N
(
h
)
D
N
(0) exp
(6.95)
0
where
m
is the average molecular mass,
g
is the free-fall acceleration, and
T
(
z
)is
the temperature at altitude
z
. For air temperature
T
300 K the barometric formu-
la (6.95) gives that the number density of molecules decreases twice at an altitude
of 6 km. Note that because of convection the concentration of the air components
does not vary up to altitudes of the order of 100 km, where the ionization processes
start and the atmosphere content varies.
To determine the change of temperature with altitude, one can ignore heat trans-
fer processes, and employ the adiabatic law
TN
1
γ
D
D
1.4 is
the adiabatic exponent for air at the temperatures considered. This leads to the
equation
dT
/
T
const, where
γ
D
D
(
γ
1)
dN
/
N
, and from the barometric formula (6.95) we
have
dN
/
N
D
mgdz
/
T
. Hence, the temperature gradient in the atmosphere
is
14 K/km. The real value (5-10 K/km) is lower than
this because of water vaporization in the atmosphere and other heat transport pro-
cesses. Nevertheless, near the Earth's surface the temperature of the atmosphere
drops in accordance with the adiabatic model up to the tropopause at an altitude of
(12
dT
/
dz
D
mg
(
γ
1)
D
˙
˙
20 K. Note that various atmospheric pa-
rameters vary depending on latitude and time of day, and we now deal with mean
4) km, where the temperature is 200
