Lecture 11_Baskar Malwa (1).pptx

E N V I R O N M E N TA L E N G I N E E R I N G : C E 3 0 0 9 D
Dr. BHASKAR S
ASSISTANT PROFESSOR
DEPARTMENT OF CIVIL ENGINEERING
MODULE 1: LECTURE 3
NATIONAL INSTITUTE OF TECHNOLOGY CALICUT
19-04-2023 1

AIR POLLUTION
🠶 Air pollution is defined as the presence of unwanted and
undesirable foreign particles and gases in the air which may have
adverse effects on human beings, animals, plants, vegetation and
important structures.
POLLUTANT
🠶 Any substance present in the environment in harmful concentration
which adversely alters the environment by damaging the growth
rate of a species and by interfering with the food chains is toxic and

CLASSIFICATION OF AIR
POLLUTANTS
Air pollutants
Based on Origin
Based on states of
matter
Based on presence in
environment
Particulate air
pollutants
Gaseous air
pollutants
Secondary
air pollutants
Primary air
pollutants
Indoor air
pollutants
Outdoor air
pollutants

ACCORDING TO
ORIGIN
 (a) Primary Pollutants
 (b) Secondary Pollutants
 PRIMARYPOLLUTANTS:- Primary pollutants are
those which are directly emitted from
identifiable source
🠶 These pollutants are emitted directly to the atmosphere.
🠶 e.g.
(a)Particulate matter
(b)Oxides of Sulphur
(c)Oxides of Nitrogen
(d)Carbon Monoxide

 SECONDARY AIR POLLUTANTS:- Secondary air pollutants
are those which are produced in the air by the reaction of two
or more primary pollutants.
🠶 e.g.
🠶 Ozone
🠶 Formaldehyde
🠶 Photochemical smog
🠶 Peroxy acetyl nitrate (PAN)

CLASSIFICATION BASED ON STATES OF
MATTER
 1. Gaseous air pollutants
 2. Particulate air pollutants
 GASEOUS AIR POLLUTANTS
• 🠶 Gaseous air pollutants are those air pollutants which are found in
the gaseous state at normal temperature and pressure in the
atmosphere.
• 🠶 The most common gaseous air pollutants are:
• 🠶Carbon monoxide
• 🠶Carbon dioxide
• 🠶Nitrogen oxides
• 🠶Sulpher oxides

PARTICULATE AIR
POLLUTANTS
🠶 These may be liquid or solid. The particulate matter are
identified as aggregates which are
larger than 0.002 µ but smaller than 500 µ
🠶 Dust (1 To 10,000 µ) : Small solid particles resulting
from break up of large masses through processes such as
crushing, grinding or blasting.
🠶 Smoke ( 0.5 To 1 µ) Consist of finely divided solid
particles produced by incomplete combustion of organic
particles such as coal, wood, or tobacco.
🠶 Mist ( 0.1 To 10 µm) :- These are liquid particles
formed by condensation of vapor.

🠶 Fog (1 to 40 µ ):- High concentration of mist is called as
fog. It is the dispersion of liquid particles in the air.
🠶 Fumes ( 0.03 to 0.3 µ ):- Fine solid particles formed by
the condensation of vapours of solid material. The fumes are
generally emitted from melting operations.
🠶 Ash ( 1 to 1000 µ ):- fine, noncombustible particles are
known as fly ash.
🠶 Spray (10 to 1000 µ):- Liquid particles formed by
automation.

CLASSIFICATION BASED ON PRESENCE IN
ENVIRONMENT
• 🠶 1. Indoor air pollutants
• 🠶 2. Outdoor air pollutants
 Indoor Air Pollutants
• 🠶 The air pollutants which are generated by households are
called indoor air pollutants.
• 🠶Cleaning agents
• 🠶Mosquito repellents
• 🠶Pesticides
• 🠶Cigarette smoke
• 🠶Gases from stoves etc.

🠶 The air pollutants which are generated outside the
buildings are called outdoor air pollutants.
🠶Automobile pollutants
🠶Industrial pollutants
🠶Mining pollutants
🠶 Natural emissions from decaying matter and animals
etc.
 Outdoor Air
Pollutants

SOURCES OF AIR
POLLUTION
🠶 The sources of air pollution may be classified into two groups:
🠶 1. Natural sources
🠶 2. Man made sources
 NATURAL SOURCES
🠶 The following are the different forms of natural sources:
🠶Atmospheric reactions 🠶Microorganisms
🠶Volcanic eruptions 🠶Radioactive substances
🠶Forest fires
🠶Dust storms, electric storms
🠶Salt spray form oceans

 MAN MADE SOURCES
🠶 Combustion of fuel 🠶 Nuclear explosions
🠶 Air crafts 🠶 Mining
🠶 Wastewater treatment plant
🠶 Automobile exhaust
🠶 Industries
🠶 Thermal and nuclear power plants
🠶 Agricultural activities
🠶 Construction materials
🠶 System of sanitation

FACTORS AFFECTING POLLUTANT DISPERSION
• Wind velocity Ambient temperature
• wind speed
• Emission rate of pollutant
• Stack height
• Stack diameter
• Exit velocity of gas
• Wind direction
• Atmospheric stability
• Exit Temperature of the gas
• Atmospheric pressure

Structure of the Atmosphere
•
Atmosphere consists of 4
layers
• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere

• LAPSE RATE
• The temperature of the ambient air normally decreases with
increases in altitude (height), this change in temperature is called
called the lapse rate.
• Environmental lapse rate:
• The prevailing lapse rate at a particular time and a particular
particular place and determined by sending a balloon equipped
with a thermometer called the Environmental 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 (DALR) is the rate of fall in
temperature with altitude for a parcel of dry or unsaturated air
(air with less moisture, to keep it simple) rising under adiabatic
conditions.
• Wet Adiabatic lapse rate (WALR): When an air parcel that is
saturated with water vapour rises, some of the vapour will
condense and release latent heat. This process causes the parcel to
cool more slowly than it would if it were not saturated.

• The three major relative
positions:
• When ELR >ALR = the environment is said to be unstable &
super adiabatic lapse rate.
• When ELR<ALR = the environment is said to be stable & sub-
adiabatic lapse rate.
• When ELR = ALR = the environment is said to be neutral.

IMPACT OF WIND ON DISPERSION OF
POLLUTANT
• Pollutants that cannot be transported or dispersed into the
upper atmosphere quickly become trapped at ground level and
pose a significant risk to human health and the environment.
• Six types of air pollution plumes illustrate the relationship
between atmospheric stability and pollutant emissions:
• looping plumes, fanning plumes, coning plumes, lofting
plumes, fumigating plumes, and trapping plumes.

ATMOSPHERIC STABILITY AND TEMPERATURE
INVERSIONS LAPSE RATE:
• The atmosphere is said to be unstable as long as a rising parcel of
air remains warmer than the surrounding air.
• When a rising parcel of air arrives at an altitude in a colder and
denser state than the surrounding air. Under such conditions
atmosphere is said to be stable.

INVERSION
S
• If the cold layer of air at ground level is covered by warmer air at
a higher level
• vertical air movement is stopped
• during a temperature inversion, the atmosphere is stable and very
little turbulence or mixing takes place
• occurrence in the autumn and winter months

PLUME BEHAVIOUR:
• Plume refers to the path and extent in the atmosphere of
the gaseous effluents released from a source usually a
stack
• The behavior of a plume emitted from any stack depends
on localized air stability.
• The behavior and dispersion of a plume entirely depend
on the environmental lapse rate (ELR).

Six types of Plume
Behavior
• Looping
• Coning
• Fanning
• Lofting
• Fumigation
• Trapping

Coning
• A type of plume which is shaped like a CONE
• Takes place near neutral atmosphere, when the wind
velocity is greater than 32 km/hr

• a type of plume emitted under extreme inversion
conditions.
• Plume will spread horizontally
Fanni
ng

• plume which has a wavy character.
• occurs in a highly unstable atmosphere because
of rapid mixing.
Loopin
g

• when there is a strong lapse rate above a surface
inversion.
• diffusion is rapid upwards
• Ideal for dispersion air pollutants and protection
of living beings to great extent.
Loftin
g

• A phenomenon in which pollutants that are
emitted into the atmosphere are brought rapidly
to the ground level when the air destabilizes.
• It is extremely bad for dispersion of pollutants.
Fumigatio
n

• When inversion layer exists above the stack and as well as
below the stack, the plume neither goes up nor goes
down, rather trapped between these two inversion layers.
• The lofting plume is most favorable air to minimizing air
pollution.
Trapping

19-04-2023 40
The basic Gaussian dispersion model applies to a single point
source such as a smokestack,
but it can be modified to account for line sources (such as emissions
from motor vehicles along a highway), or area sources (these can be
modelled as a large number of point sources).
Consider just a single point source such as that shown in Figure.
The coordinate system has been set up to show a cross-section of
the plume, with z representing the vertical direction and x the
distance directly downwind from the source.
Gaussian Plume
Model

19-04-2023 42
 We were to observe the plume at any particular instance, it
might have some irregular shape, such as the outline of the
looping plume shown. A few minutes later, however, the
plume might have an entirely different boundary.
 Since stack emissions have some initial upward velocity and
buoyancy, it might be some distance downwind before the
plume envelope might begin to look symmetrical about a
centre line.
 The centerline would be somewhat above the actual stack
height.
 The highest concentration of pollution would be along this

19-04-2023 43
Gaussian plume model assumes that the pollutant concentration
follows a normal distribution about this centerline in both the
vertical plane, as shown in the figure, and in the horizontal
direction, not shown.
Emissions as if they came from a virtual point source along the
plume centerline, at an effective stack height H.
The Gaussian point-source dispersion
equation relates average, steady-state
pollutant concentrations to the source
strength, windspeed, effective stack height,
and atmospheric conditions.

19-04-2023 44
• The rate of emissions from the source is constant.
• The windspeed is constant both in time and with
elevation.
• The pollutant is conservative; it is not lost by decay,
chemical reaction, or deposition. When it hits the
ground, none is absorbed, and all is reflected.
• The terrain is relatively flat, open country.

19-04-2023 45
At the origin, with distance directly downwind is given by x, the
distance off the downwind axis is specified by y, and the elevation
is given by z.
Since our concern is going to be only
with receptors (people and
ecosystems) at ground level, the form
of the Gaussian plume equation given
here is less general than it can be and
applies only to z = 0.

19-04-2023 47
Downwind Ground Level Concentration

19-04-2023 48
The ground-level concentration of pollution directly downwind
of the stack is of interest since pollution will be highest along
that axis.
With y = 0,
Downwind Ground Level
Concentration
The Gaussian Dispersion Coefficients

19-04-2023 57
Plume Rise
The difference between the actual stack height h and the effective
height H is called the plume rise.
Plume rise is caused by a combination of factors, the most
important ones being the buoyancy and momentum of the
exhaust gases, and the stability of the atmosphere itself.

Lecture 11_Baskar Malwa (1).pptx

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