This Power Point Presentation has the contents of Unit 2 of CE8005 Air Pollution and Control, as per Anna University Curriculum.

1. CE8005 Air Pollution and Control
Unit 2
Effects of meteorology on Air Pollution -
Fundamentals, Atmospheric stability, Inversion,
Wind profiles and stack plume patterns-
Atmospheric Diffusion Theories – Dispersion
models, Plume rise.

2. Meteorology
• Branch of science concerned with processes
and phenomena of atmosphere, especially as
a means of forecasting the weather.
• Factors which change the concentration of
pollutants in particular area is known as
Meteorological factors.
• Concentration of air pollutants in a particular
area depends on local weather conditions.

3. Objectives of Meteorological Factor Study
• To identify the source of pollutants
• To predict pollution events such as high
concentration days
• To simulate and predict air quality using
computer models
• To determine stack height
• To evaluate the intensity of air pollution

4. Meteorological Factors
• Primary Factors
- Wind speed and direction
- Temperature
- Atmospheric Stability
- Mixing Height
• Secondary Parameters
- Rainfall and precipitation
- Humidity
- Solar Radiation
- Visibility

5. Wind Speed and Direction
• Speed and direction of wind changes the
concentration of pollutants, especially near ground
level
• High speed of wind carries away the pollutants near
the point of emission
• Emitted air pollutants easily get diluted with high
volume of atmospheric air
• Speed of dilution process depends on speed and
direction of wind

6. Formula for calculating wind speed
Zo Anemometer Height
Z- Height where wind speed is to be
measured
Uo - Wind speed at Zo
K – Wind speed constant
1/9 for larger lapse rate
1/3 for marked inversions
1/7 general value used for calculations

7. Gustiness
• A characteristic which determines the extent to which
pollutants are diluted and mixed with surrounding air.
• It directly proportional to the wind speed.
• In plain terrain, wind speed and direction near source
decide the subsequent movement of pollutants.
• In hilly terrain, hills may deflect the air flow either
horizontally, vertically or both.
• Quantity of deflection depends upon vertical stability of
atmosphere.
• Wind speed is measured by anemometer.

8. Atmospheric Stability and Inversion
• The tendency of atmosphere to encourage or
discourage vertical motion.
• Vertical motion is directly related to atmospheric
conditions.
• For every 1000 ft in altitude, there will be a
temperature decrease of 6.4 o C/km.
• The rate at which the atmospheric temperature
decreases with increase in altitude is called lapse rate
• Inversion : When the reverse lapse rate occurs, a
dense-cold stratum of air at ground level gets covered
lighter warm air at higher level.

9. Inversion
• A reversal of the normal decrease of air temperature
with altitude, or of water temperature with depth.
• When the reverse lapse rate occurs, a dense-cold stratum
of air at ground level gets covered lighter warm air at
higher level.
• During inversion vertical air movement is stopped.
• Pollution will be concentrated below the inversion layer.
• Due to this temperature inversion, the atmosphere is
stable.
• This is called atmospheric stability.
• At this condition the pollutants in the air do not dilute.

10. Inversion

11. Types of Inversions
Radiation Inversion
• The cool air stratum is covered with light
warm air.
• The vertical air movement is stopped until sun
warms the lower air in the next morning.
• Very common in winter than summer.
• It is due to reduced day times.
• Due to horizontal air movement, ground
radiation inversion occur frequently in valley
areas.

12. Subsidence Inversion
• Inversion occurring at moderate altitudes and
often remains for several days.
• It is caused by sinking or subsiding of air anti-
cyclones.
• The air circulating around the area descends
slowly at the rate of 1000 m per day.
• Anti-cyclone – High pressure area surrounded
by low pressure area

13. Mixing Height
• Height above the earth’s surface to which
related pollutants will extend.
• It is due to the action of atmospheric
turbulence.
• It is usually related to
- Wind direction
- Wind Speed
- Wind turbulence

14. Precipitation and Rainfall
• Secondary
meteorological factors
that exert two-fold
cleansing action on
pollutants.
• Rainfall accelerates the
deposition of particulate
matter on the ground.
• Rainfall can be estimated
by rain gauges.

15. Humidity
• Moisture content in atmosphere influences
the corrosive action of air pollutants.
• It represents for fog formation.
• Quantity representing the amount of water
vapour in the atmosphere.

16. Solar Radiation
• Induces the chemical reaction between atmospheric
air components and pollutants in the air.
• The reaction depends on the location.
• Solar radiation is the main heat source and it is
absorbed at ground level.
• Solar radiation plays a vital role in establishing the air
quality criteria.

17. Lapse Rate
• Adiabatic lapse rate: Change of temperature with a change in
altitude of an air parcel without gaining or losing any heat to the
environment surrounding the parcel.
• Dry adiabatic lapse rate: Dry parcel of air. Air cools 9.8°C/km rise
in altitude (5.4°F/1000 ft).
• Wet adiabatic lapse rate: As parcel rises, H2O condenses and
gives off heat, and warms air around it. Parcel cools more slowly
as it rises in altitude, ≈6°C/km (≈3°F/1000 ft).
• Ambient or prevailing lapse rate: The
actual atmospheric temperature change with altitude;
• Not only does water content modify lapse rates.
• But wind, sunlight on the Earth’s surface, and geographical
features change actual lapse rates.

18. Summary of Various Adiabatic Conditions

21. Plume and Plume Rise
• Plume – Path and direction of emitted gas
from a source into atmosphere.
• Plume – It is an air column, in which one air is
moving into another.
• Plume Rise – Distance of hot plume from the
stack into the atmosphere due to the
buoyancy and momentum.

22. Factors influencing Plume Behaviour
• Stack height
• Diurnal Variation
• Seasonal variation

23. Stack Height
• Emission from tall stacks are allowed to mix with
atmospheric air.
• It increases rate of dilution
• Ground level contamination of emission depends on
height of stack and height of plume rise
• Immediately above the stack the rise of pollutant is
proportional to emission velocity of gases.
• It also depends upon the temperature difference
between the gases and surrounding temperature.

24. Effective Stack Height

25. Effective Stack Height
• Effective Stack Height, H = h+ Δh
Where
H – Actual height of stack in m
Δh – Plume height in m

26. Point Source Gaussian Plume Model

27. Effective Stack Height

28. Plume Behaviour

29. Types of Plume (Plume Pattern)
• Looping Plume
• Neutral Plume
• Coning Plume
• Fanning Plume
• Lofting Plume
• Fumigating Plume
• Trapping Plume

30. Looping Plume
• Wavy character
• Occurs at highly unstable atmosphere
• It is due to rapid mixing

31. Neutral Plume
• Upward vertical rise of plume
• Occurs when environmental lapse rate is
approximately equal to adiabatic lapse rate
• Upward movement of plume will continue till
the plume density equals air density

32. Coning Plume
• Behaviour plume in the shape of cone
• Occurs in slightly stable environment
• When wind velocity is more than 32 km/h
coning plume occurs in neutral atmospheric
condition.
• Plume reaches ground at greater distances
than looping plume.

33. Fanning Plume
• Horizontal plume pattern for long distance
• Occurs when there is no vertical mixing
• Occurs under extreme inversion conditions,
due to negative environmental lapse rate from
ground level to certain heights.

34. Lofting Plume
• Occurs when there is a strong super adiabatic lapse
rate above inversion.
• Diffusion is rapid in upward direction.
• Diffusion does not penetrate the inversion layer in the
downward.
• Emission will not reach the ground surface.
• It is the best among all plume patterns.

35. Fumigating Plume
• It occurs at a short distance above stack height.
• Strong lapse rate prevails below the stack.
• Because of inversion layer, emission cannot move
above top of stack.
• It is the worst case of plume pattern, as it brought
down near the ground.

36. Trapping Plume
• When the inversion layer exists above and
below the plume layer the plume lies between
the inversions.
• Dispersion cannot go above a certain height

37. Wind Rose
• Pictorial representation of distribution of wind
direction at the given location over a
observation period.
• Used to show the prevailing wind direction.
• Used to view how the wind speed and
direction is typically distributed over a
particular location.
• Essentially used in construction airport
runways, to ensure best landing and take-off
in to the wind.

38. Wind Rose Diagram
• Wind rose diagram consists of eight or 16 emerging lines from
a circle.
• Emerging line indicates the wind direction.
• Length of each line specifies the frequency of wind direction.
• Frequency of calm condition is entered in the centre of the
diagram.
• Wind roses may be drawn from the data obtained over the
given time.
• Time interval may be several months or a year or a season.
• It is prepared using a scale to indicate percentage of
frequencies with appropriate shades, lines etc.
• Wind speed less than 1 km is mentioned as calm.

39. Wind Rose Diagram

40. Types of Wind Rose
• Precipitation wind rose
• Smoke wind rose
• So2 wind rose
• HC wind rose

41. Pollution Roses
• In a wind rose diagram, various parameters
lime precipitation, smoke, SO2, HC are
attached with wind direction instead of speed.
• Type I – shows the direction and duration of
wind
• Type II – Shows the direction, duration and
intensity of wind

42. Plume Rise and Dispersion Theory
First Stage – Hot plume from stacks goes upto a certain
distance called “plume rise”
- it is due to buoyancy and momentum
Second Stage – Plume spreads both vertically and
horizontally by dispersion process

43. Plume Rise and Dispersion Theory
• Plume Temperature
• Rate of Emission
• Stack Parameters
- Height and diameter
- Wind speed and direction
- Atmospheric Stability
- Topography of region

44. Wind Tunnel

45. Things can be tested in Wind Tunnel

46. Methods of Measuring Meteorological Factors
• The National Environment Engineering
Research Institute (NEERI) has developed the
following instruments
• Wind Direction Recorder
• Wind Speed Recorder
• Temperature Measurement
• Solar Radiation Measurement

47. Wind Direction Recorder
• Operated
mechanically without
any power supply.
• Continuously records
the wind direction on a
chart attached with the
instrument.

48. Types of Wind Vanes
• Flat plate wind vane
• Splayed vane
• Aerofoil vane
• Running average anemograph

49. Types of Wind Vanes

50. Flat Plate Wind Vane
• Vertical plane is the sensing
element.
• Sensing element governs
azimuth angle of a vertical shift.
• It is mounted at one end of
horizontal rod.
• A counter weight is mounted at
the other end.
• The rod is fastened to a vertical
shaft.
• Wind pressure acting on flat
plate keeps the counter weight
heading in the wind.

51. Splayed Vane
• Two flat plates joined at
small angle at one end of
horizontal rod.
• It acts as wind direction
sensor.

52. Aerofoil Vane
• Vane has aerofoil cross section with span
often being three or four times the chord.

53. Running Average Anemograph
• It is always better to measure both average
wind speed and direction
• While averaging there is a problem in
differentiating 0o and 360o
• Because wind direction fluctuates around
north.
• An anemograph automatically produces
average of both wind speed and direction.

54. Wind Direction Aloft
• Wind direction at the height of a plume from
one or more stacks is essential for analysis.
• The following are the methods.
- Pilot Balloons (Pibals)
- Tetroons
- Kite Balloons
- Radio and Rador
- Smoke Trails

55. Pilot Balloons (Pibals)

56. Pilot Balloons (Pibals)
• A ceiling balloon also called a pilot balloon or pibal, is used
by meteorologists to determine the height of the base
of clouds above ground level during daylight hours.
• A theodalite is used to track the balloon in order to
determine the speed and direction of winds aloft.
• The principle behind the ceiling balloon is that timing of a
balloon with a known ascent rate (how fast it climbs) from its
release until it disappears into the clouds.
• It can be used to calculate the height of the bottom of the
clouds.

57. Tetroons

58. Tetroons
• A solar balloon is a balloon that gains buoyancy when the air
inside is heated by solar radiation
• The colour of balloon is usually black or any dark material.
• The heated air inside the solar balloon expands and has lower
density than the surrounding air.
• A solar balloon is similar to a hot air balloon.
• A vent at the top can be opened to release hot air for descent
and deflation.

59. Kite Balloons
• A kite balloon is a tethered
balloon which is aerodynamically
optimised for windy conditions.
• It is made directionally stable and
by minimising aerodynamic
resistance to the wind, or drag.
• It typically comprises a
streamlined envelope with
stabilising features and a harness
or yoke connecting it to the main
tether.
• The first reliable way to fly and
land in the same place

60. Smoke Trails
• Information on wind direction
aloft obtained by intervals the
position in space of smoke.
• Smoke is released above ground
by rising a rocket or aeroplane.
• However, observations during
fog, smoke at night are not
possible.
• This method requires skilled
person when compared to pilot
balloon method.

61. Wind Speed Recorder
• Four cup rotor is employed
to sense the wind.
• The motion of cup is
transferred after reducing
speed by gear system.
• Further to a pen which
makes continuous rise and
fall impression on chart
paper.
• Rate of rise or fall is
proportional to wind speed.

62. Universal Wind Meter

63. Humidity Psychrometer
• Simplest and reliable instrument is a whirling
psychrometer.
• Two thermometers (dry and wet) are whirled
in the air.
• The temperatures of both dry bulb wet bulb
are noted.
• From the difference between dry bulb and
wet bulb thermometers relative humidity can
be found by psychrometric table or chart.

64. Temperature Measurement
• Common instrument used for measuring
temperature is thermometer.
• Types of thermometer.
- Mercury thermometer
- Electrical resistance thermometer
- Bi-metallic thermometer
- Digital thermometer

65. Principle of Working of Thermometers
• Mercury Thermometer – Thermal expansion
of Hg
• Bimetallic Thermometer – Differential
expansion of metals
• Electrical Resistance Thermometer – Variation
in electrical resistance of a metallic wire and a
thermocouple.

66. Thermometers
Mercury Thermometer Bimetallic Thermometer

67. Electric Resistance Thermometer
• Uses a sensitive element made of extremely pure metals like
platinum, copper or nickel.
• The resistance of the metal is directly proportional to the
temperature.
• Mostly, platinum is used in resistance thermometer.
• The platinum has high stability, and it can withstand high
temperature.
• Gold and silver are not used for RTD because they have low
resistivity.
• The copper has low resistivity and also it is less expensive.
• The only disadvantage of the copper is that it has low
linearity.

68. Electric Resistance Thermometer
• The resistance thermometer is placed inside the protective tube for
providing the protection against damage.
• The resistive element is formed by placing the platinum wire on the
ceramic bobbin.
• The resistance element is placed inside the tube which is made up
of stainless steel or copper steel.
• The lead wire is used for connecting the resistance element with
the external lead.
• The lead wire is covered by the insulated tube which protects it
from short circuit.
• The tip of the resistance thermometer is placed near the
measurand heat source.
• The heat is uniformly distributed across the resistive element.
• The changes in the resistance vary the temperature of the element.

69. Solar Radiation Measurement
• In places where, photochemical smog takes
place, solar radiation measurement is
essential.
- Pyrheliometer
- Solarmeter
- Chemical actinometer

70. Dispersion Models
• Mathematical simulation or approaches made
to study about dispersion of pollutants.
• Dispersion models depend upon mathematical
calculations.
• Dispersion models require,
- Meterological factors
- Source of emission
- Emission parameters
- Terrain elevation at source location

71. Types of Air Pollution Models
• Box Model
• Gaussian Model
• Lagrangian Model
• Eulerian Model
• Dense Gas Model

72. Applications of Dispersion Model
• Air Quality Assessment
• Estimation of downwind ambient conditions
• Calculation of toxins emitted from sources
such as
- Industrial plants
- Vehicular traffic
- Accidental chemical releases

73. Thank You
Dr A R Pradeep Kumar, B.E., M.E., Ph.D.
Professor and Head/Mech.
Dhanalakshmi College of Engineering
Chennai 601 301
Email : dearpradeepkumar@gmail.com
99 41 42 43 37