1. Fundamentals of air Pollution Engineering
METEOROLOGY

2. The science of meteorology has great bearing on air pollution
The science of meteorology has great bearing on air pollution. An air pollution problem involves three parts: the source, the movement of the pollutant and the recipient. All meteorological phenomena are a result of interaction of the elemental properties of the atmosphere, heat, pressure, wind and moisture. In this lecture we will discuss the meteorological conditions, which directly influence the transport and dispersion of pollutants.

3. METEOROLOGY Pure air is a mixture of gases, containing; 78.0% nitrogen
20.1% oxygen
0.9% argon
0.03% carbon dioxide
0.002% neon
0.0005%helium
but pure air is not found in nature and is of interest only as reference.

4. Earth atmophere can be divided into four major layers:
Troposphere – where most of our weather occurs, ranges from 5 km at the poles to about 18 km equator. The temperature decrease with altitude. Over 80% of air is within this well-mixed layer.
Stratosphere – a layer of air where the temperature profile is inverted and in which little mixing take place. Pollutant that migrate into this layer can stay for many years. This layer has a high ozone concentration.
Mesosphere and Thermosphere – contain only about 0.1 % of the air.
Air pollution problem occur in the troposhere. Pollutants in the troposphere wheather produced naturally or emitted from human activities are moved by air currents that we call wind. Wind not only moves the pollutants horizontally, but causes the pollutants to disperse, reducing the concentration of the pollutant with distance away from the source.

5. Thermosphere A L T I TUD E Mesosphere Stratosphere (km) Troposphere20 40 60 80
100 A L T I
TUD E
(km)
Troposphere
Stratosphere
Mesosphere
Thermosphere
200
300
400
Temperature (K)

6. Stability
Stability is the tendency of the atmosphere to resist and enhance vertical motion.
Lapse rate is the change of air temperature with height. It is used as indicator as the stability condition of the atmosphere. There are 3 stability categories that are:
Neutral atmosphere
Unstable atmosphere
Stable atmosphere

7. a) Neutral Atmosphere
The lapse rate for a neutral atmosphere is defined by the rate of temperature increase or decrease experienced by the parcel of air that expands or contracts adiabatically (without addition or loss of heat) as it raised through the atmosphere.
The rate of temperature decrease (dT/dZ) is called dry adiabatic lapse rate and it is designated by Г.
dT/dZ is approximately -1.00OC/100 m.

8. Stability
From the figure, since the ambient lapse rate is equal to Г so the atmosphere is said to have neutral stability.

9. b) Unstable Atmosphere
If the temperature rate of atmosphere is greater than Г, the lapse rate is said to be superadiabatic and the atmophere is unstable.
If we capture a ballon full of polluted air at elevation A and adiabatically displaced the ballon at 100 m above (B), the temperature inside the ballon will decrease 1 OC (according to Г).
The temperature outside the balloon will decrease to OC at elevation B (according to ambient lapse rate of –1.25 OC/100 m).
Since the outside air is cooler than inside, the balloon will have tendency to rise.
If we displace the balloon adiabatically to elevation C the temperature inside the balloon will increase to OC, while the ambient temperature would increase to OC. The inside air will be cooler than the outside air thus results the balloon to sink.

11. c) Stable Atmosphere
If the temperature of the atmosphere falls at the rate less than Г, it is called subadiabatic and the atmosphere is stable.
If we capture a ballon full of polluted air at elevation A and adiabatically displaced the ballon at 100 m above (B), the temperature inside the ballon will decrease 1 OC (according to Г).
The temperature outside the balloon will decrease to OC at elevation B (according to ambient lapse rate of –0.5 OC/100 m).
Since the inside air is cooler than outside, the balloon will have tendency to sink.
If we displace the balloon adiabatically to elevation C the temperature inside the balloon will increase to OC, while the ambient temperature would increase to OC. The balloon will be warmer than the ambient air thus results the balloon to rise.

12. There are 2 special cases of subadiabatic lapse rate:
Isothermal – No changes of temperature with elevation.
Inversion – The temperature increases with elevation. It is the most severe form of stable atmosphere but when it occur it often asociated with restricted air volumes that cause air pollution

13. EXAMPLE
Given the following temperature and
elevation data, determine the stability of the
atmosphere.
Z,m Temperature (OC)

14. SOLUTION
1) Begin by determining lapse rate:
= – (-3.05) = OC/m
318 – 2
= -0.01OC x 100m = -1.00OC m
2) Compare with Г and find that they are equal. Thus the atmospheric stability is neutral.

15. Plume Types The plume (smoke trail) from a tall stack located on flat
terrain has been found to exhibit a charecteristic shape that
is dependent on the stability of the atmosphere. There are 5
plume types that are:-
Looping plume – Occur in highly unstable conditions. Unstable conditions are generally favorable for pollutant dispersion, momentarily high ground-level concentrations can occur if the plume loops downward to the surface.
2) Coning plume – is characteristic of neutral conditionsor slightly stable conditions. It is likely to occur on cloudy days and sunny days before the development of unstable daytime condition.

16. Fanning plume – Occur in stable conditions
Fanning plume – Occur in stable conditions. The inversion lapse rate discourages vertical motion without prohibiting horizontal motion and the plume may extend downwind from the source for a long distance. Often occur in the early morning.
Lofting – When conditions are unstable above an inversion, the release of a plume above the inversion results in effective dispersion without noticeable effects on ground level concentration around the source.
5) Fumigation and trapping – If the plume is released just under an inversion layer, a serious air pollution situation could develop. When the instability reaches the level of the plume that is still trapped below the inversion layer, the pollutants can be rapidly transported down toward the ground.

18. Plume Types
Plume types are important because they help us understand under what conditions there will be higher concentrations of contaminants at ground level.

19. Looping Plume High degree of convective turbulence
Superadiabatic lapse rate -- strong instabilities
Associated with clear daytime conditions accompanied by strong solar heating & light winds
High probability of high concentrations sporadically at ground level close to stack.
Occurs in unstable atmospheric conditions.

20. Coning Plume Stable with small-scale turbulence
Associated with overcast moderate to strong winds
Roughly 10° cone
Pollutants travel fairly long distances before reaching ground level in significant amounts
Occurs in neutral atmospheric conditions

21. Fanning Plume Occurs under large negative lapse rate
Strong inversion at a considerable distance above the stack
Extremely stable atmosphere
Little turbulence
If plume density is similar to air, travels downwind at approximately same elevation

22. Lofting Plume
Favorable in the sense that fewer impacts at ground level.
Pollutants go up into environment.
They are created when atmospheric conditions are unstable above the plume and stable below.

23. Fumigation
Most dangerous plume: contaminants are all coming down to ground level.
They are created when atmospheric conditions are stable above the plume and unstable below.
This happens most often after the daylight sun has warmed the atmosphere, which turns a night time fanning plume into fumigation for about a half an hour.

24. Wind Rose Diagram (WRD)
WRD provides the graphical summary of the frequency distribution of wind direction and wind speed over a period of time
Steps to develop a wind rose diagram from hourly observations are:
Analysis for wind direction
Determination of frequency of wind in a given wind direction
Analysis for mean wind speed
Preparation of polar diagram

25. Land-Sea
Valley
11/10/2018

26. Calculations for Wind Rose
% Frequency =
Number of observations * 100/Total Number of Observations
Direction: N, NNE, ,NNW, Calm
Wind speed: Calm, 1-3, 4-6, 7-10,

27. Determination of Maximum Mixing Height
Steps to determine the maximum mixing height for a day are:
Plot the temperature profile, if needed
Plot the maximum surface temperature for the day on the graph for morning temperature profile
Draw dry adiabatic line from a point of maximum surface temperature to a point where it intersects the morning temperature profile
Read the corresponding height above ground at the point of intersection obtained. This is the maximum mixing height for the day

28. Determination of Maximum Mixing Height

29. Power plant Plumes

30. Power plant Plumes

31. Try to read questions on pages 35 & 36 at the text book
Power plant Plumes
Try to read questions on pages 35 & 36 at the text book

32. Stability Conditions
Adiabatic lapse rate
Environmental lapse rate

33. Superadiabatic Lapse Rates (Unstable)
Temperature decreases are greater than -10o C/km
Occur on sunny days
Characterized by intense vertical mixing
Excellent dispersion conditions

34. Isothermal Lapse Rates (Weakly Stable)
Neutral Lapse Rates
Temperature decreases are similar to the adiabatic lapse rate
Results from:
Cloudy conditions
Elevated wind speeds
Day/night transitions
Describes good dispersion conditions
Isothermal Lapse Rates (Weakly Stable)
Characterized by no temperature change with height
Atmosphere is somewhat stable
Dispersion conditions are moderate

35. Inverted Lapse Rates (Strongly Stable)
Characterized by increasing temperature with height
Inversion

36. Plume Rise
As you can see from the preceding figure the height a plume rises is very important.
No theoretical model has been developed to predict plume rise, but several good empirical models have been developed. One of those is presented below:
)h = 2.6 [F/( u S)]1/3
)h = plume rise above stack, m
u = average wind speed, m/sec
)T/)z = prevailing lapse rate, oC/m
Vs = stack gas exit velocity, m/s
d = stack diameter, m
Ta = temperature of atmosphere, oC
Ts = temperature of stack gas, oC
F = buoyancy flux, m4sec-3
F = [gVsd2(Ts – Ta)] / [4 (Ta )]
S = [g/(Ta )] [ ()T/)z) ]

37. Example
A stack has an emission exiting at 3 m/sec through a stack with a diameter of 2 m. The average wind speed is 6 m/sec. The air temperature at the stack exit elevation is 28oC and the temperature of the emission is 167oC. The atmosphere is at neutral stability. What is the expected rise of the plume?
)h = 2.6 [F/( u S)]1/3
At neutral stability, )T/)z = 0.01 oC/m
F = [9.8 x 3 x 22 x (167 – 28)] / [ 4 ( )] = 13.6
S = [9.8 / ( )] ( ) = x 10-4
)h = 2.6 [13.6 / ( 6 x 6.51 x 10-4)]1/3 = 40 m