CE 326 – Principles of Environmental Engineering
Air Pollution Meteorology
Shane Rogers
Horizontal Atmospheric Motion
The horizontal movement of the atmosphere is driven mostly by uneven heating of the earth’s surface
and modified by the effect of the earth’s _______________________ (Coriolis effect).
Schematic representation of the circulation of the atmosphere (Frederick K. Lutgens/Edward J. Tarbuck, The
Atmosphere, 5e, 1992, p. 170, Prentice Hall, Englewood Cliffs, New Jersey.)
Local Influences on Motion in the Atmosphere
The general circulation pattern of the winds can be changed locally by ground friction and terrain
effects (mechanical turbulence), high and low pressure systems (anticyclones and cyclones), or
differences in heating and cooling rates between cities, land areas, and water bodies (thermal effects).
Figure 6.15 in your text
Vertical Atmospheric Motion
The vertical movement of the atmosphere is driven mostly by changes in air density.
Lapse rate (ambient lapse rate) – the change in air temperature with height
Dry Adiabatic Lapse Rate – the rate of temperature decrease with increasing height that would result
from an ideally behaving parcel of air that expands adiabatically (without a change in heat) as it rises.
Dry adiabatic lapse rate (dT/dz):
For fluids, the change of pressure with height can be related to the density of the fluid and the
acceleration of gravity:
where:
P=
z=
=
g=
Pressure
Vertical distance
Density of air
Gravitational acceleration
Remembering that the density of a gas can be expressed using the ideal gas law such that:

where:
GMW =
R=
T=
P(GMW )
RT
Gram molecular weight of air
Ideal Gas Law Constant (8.314 J/(K·mol))
Temperature (K)
We can rewrite the first equation:
dP
gP(GMW )

dz
RT

1
g (GMW )
dP  
dz
P
RT
For dry air, temperature and pressure both change with elevation, therefore we cannot integrate the
above equation because we need a thermodynamic expression for the change in temperature with
change in elevation.
For an ideal gas undergoing a reversible, adiabatic process:
where:
Cp =
Cv =
heat capacity of a gas at constant pressure = Cv + R
heat capacity of a gas at constant volume
Since air is 99% O2 and N2, we can assume it is diatomic. For a diatomic ideal gas, Cv = 5/2 R, and
Cp = 5/2 R + R = 3.5 R.
Setting the two expressions from dP/P equal, and substituting Cp = 3.5 R:
Cp
RT
dT  
GMW for air:
78% N2 =
21% O2 =
1% Ar =
g (GMW )
dz
RT
(0.78)(28 g/mol) =
(0.21)(32 g/mol) =
(0.01)(39.95 g/mol) =

dT
g (GMW )

dz
3.5R
21.84 g/mol
6.72 g/mol
+0.40 g/mol
28.96 g/mol
Stability – the tendency of the atmosphere to resist or enhance vertical motion

______________________________________ – thermal structure of the atmosphere
neither enhances nor inhibits turbulence (ambient lapse rate = dry adiabatic lapse rate)
Height (m)
600
500
400
300
200
100
0
19
20
21
22
23
24
25
26
Temperature (ºC)

______________________________________________ – thermal structure of the
atmosphere enhances turbulence (ambient lapse rate > dry adiabatic lapse rate) cyclones
Height (m)
600
500
400
300
200
100
0
19
20
21
22
23
24
25
Temperature (ºC)
26

_____________________________________ – thermal structure of the atmosphere
inhibits turbulence (ambient lapse rate < dry adiabatic lapse rate) - anticyclones
Height (m)
600
500
400
300
200
100
0
19
20
21
22
23
24
25
26
Temperature (ºC)
Fig. 6-14 in text
The more unstable the atmosphere, the more mixing occurs, and the larger the standard deviations, Sz
and Sy become.
A = _______________________________
F = _______________________________
 E 
 x, y,0, H   
e
 S y S z u 
 
 1  y
 2 Sy
 




2




e
 1 H
 
 2  S z




2



