Air pollution fundamentals

1. Module 1-1
Atmospheric Science (Chemistry)

2. Temperature and Pressure in the Atmosphere
• Troposphere (10-15 km) is the lowest layer of the atmosphere characterized by
decreasing temperature with height and rapid vertical mixing. Extends up to
tropopause.
• Stratosphere (∼45-55 km) extends from the tropopause to the stratopause;
characterized by increasing temperature with altitude. This leads to slow vertical
mixing.
• Mesosphere (∼80-90 km) extends from the stratopause to the mesopause;
characterized by decreasing temperature with altitude to the mesopause (coldest point
in the atmosphere) and rapid vertical mixing.
• Thermosphere is the region above the mesopause characterized by high temperatures
due to absorption of short-wavelength radiation by N2 and O2 gas and rapid mixing.
The ionosphere is a region of the upper mesosphere and lower thermosphere where
ions are produced by photoionization.
• Exosphere (>500 km) is the outermost region of the atmosphere where gas molecules
with sufficient energy are capable of escaping Earth’s gravitational attraction.
The earth’s atmosphere is characterized by variations of temperature and pressure with height.

3. Global average temperature distribution for January over 1979–1998.
• The darker line shows the height of the tropopause which is highest over the tropics (∼14–15 km) and
lowest over the poles (∼8 km).
• The coldest region of the atmosphere is in the stratosphere just above the tropical tropopause, where
temperatures are less than 200 K (73 °C).

4. Troposphere
• The troposphere (also called a lower atmosphere) is the lowest layer in the atmosphere and generally there is a
continuous drop of the temperature versus height. Depending on the time of year and the location's latitude, it
rises from the ground to a height of 12±4 km. In specifically, the troposphere rises to a height of 7-8 km above
the pole zone, compared to 16–17 km above the equatorial region.
• 80% of the atmosphere's bulk and nearly all of its water vapor are found in the troposphere. As a result, the
troposphere is the most crucial layer for meteorology because it is where all atmospheric processes and weather
dynamics take place.
Main Characteristics: • Temperature decline that is steady and uniform with height. The temperature is
dropping at a pace of about 6.5°C/km.
• Since the influence of the Earth's surface friction is more pronounced at lower heights,
the wind velocity increases with height. The upper layer of the troposphere is where the
most velocity is seen.
• The troposphere contains nearly all of the water in all three states (solid, liquid, and
vapour), with the lower layers having the highest concentration.
• The troposphere is where the weather events take place.

5. Tropopause
• The tropopause, or space between the troposphere and the stratosphere, is the upper part of the troposphere.
In relation to latitude, the tropopause's height varies. As a result, there are two types of tropopause: tropical
and polar. The polar tropopause occurs at higher latitudes, whereas the tropical tropopause occurs at lower
latitudes and only affects regions with latitudes of 35 to 40 degrees.
The mean height of the
tropopause at different
regions is:
• 16–17 km at the equatorial regions.
• 11–12 km at the temperate regions.
• 7–8 km at the polar regions.
• Tropopause temperatures range from 55 to 60 degrees Celsius over regions of medium latitude and from 70 to
80 degrees Celsius above equatorial regions. Inside the layer of the tropopause, the temperature width is
narrow, and as a result, the temperature change versus height is virtually always constant.

6. • The boundary layer is the lower layer of the troposphere that is immediately impacted by the Earth's surface and
responds to changes in that surface at intervals no longer than one hour.
• The boundary layer's upper level is defined as the height where the wind stops turning. The height of the boundary
layer above the oceans varies slowly across time and space due to the daily cycle of the modest shift in sea surface
temperature. Because of its high heat capacity, water can absorb a lot of heat without significantly changing its
temperature.
• The boundary layer both above sea and land tends to be thinner at areas of high pressure and the air is transported
to areas of low pressure.
Boundary layer

7. Mixing layer Residual layer Nocturnal boundary layer
The mixing layer is a stable layer that acts as a
boundary, preventing warm air masses from
ascending further and thus constraining
turbulence.
Half an hour after sunset, there is no further
formation of thermal fluxes, and air turbulence
gradually decreases. Rather, a well-mixed layer of
air is formed, which is referred to as the residual
layer because the air pollution levels are the same
as at the mixing layer.
Due to the influence of the Earth's surface, the
lower part of the residual layer forms a stable
layer of air during the night. This layer is
considered stable, with only minor turbulence
influence.
This layer experiences turbulence as a result of
radiation leakage from lower clouds as well as
heat and momentum from the Earth's surface.
Because the residual layer remains for a short
time after sunrise, photochemical reactions
within it are favored.
The statistically stable layer reduces turbulence,
but the nocturnal jet creates air streams that
cause turbulent movements. As a result, locally
intense turbulence can appear in this stable layer.
Unlike the mixing layer during the day, the stable
layer during the night has no upper limit.
The maximum height of the mixing height is
observed late in the afternoon. The mixing layer
can be increased with the entrainment of air from
the free atmosphere.
The residual layer is not in direct contact with the
surface of the Earth. The nocturnal layer grows in
height during the night, changing the base of the
residual layer.
Pollutants emitted inside the stable layer at night
move very slowly in the vertical direction. This is
referred to as fanning.
The major air pollution sources are located near
the Earth’s surface and therefore the
concentration of air pollutants has higher values
in the mixing layer compared to the free
atmosphere.
Because the remaining part of the residual layer is
not affected by turbulence and the surface's
effect, it is not part of the boundary layer. Many
studies, however, incorporate the residual layer
into the boundary layer.
This stable layer can form even during the day
when the Earth's surface is colder than the air
above it. These conditions are observed when a
warm air stream passes above a cold surface
(warm front) or close to coast lines.

8. Stratosphere
• The stratosphere is the atmospheric layer that exists above the troposphere and is separated from it by the
tropopause. The stratosphere reaches a height of 50-55 km.
• The air temperature from the tropopause to the next 20 km does not vary significantly with height. Above this
elevation, the temperature rises until it reaches the stratopause, where it is close to 0 degrees Celsius. The
absorption of ultraviolet Sun radiation by ozone is primarily responsible for the temperature increase with height.
• Because temperature increases with height in this region, the stratosphere is considered a more stable layer than the
troposphere.
• The region of the stratosphere up to 35 km in height is often referred to as the "lower stratosphere," while the rest is
referred to as the "upper stratosphere." The lower stratosphere is distinguished by its relatively low temperature
values and high drought. This is due to the low temperatures (between 40 and 50 degrees Celsius) in this layer, which
prevents significant humidity from forming.
The stratopause is the area between the stratosphere and the atmospheric layer above it. This
layer is almost isothermal and exists at a height of 50 to 55 km. The maximum temperature
that occurs in the stratospheric layer is also observed in this layer.
Stratopause

9. Mesosphere The mesosphere is the atmospheric layer that follows the stratopause and extends up to
80-85 km. The mesosphere is distinguished by an abrupt drop in temperature versus
height, which reaches values close to 90°C or lower in the upper zone. The lack of ozone
is responsible for the temperature drop.
Thermosphere • The thermosphere is the atmospheric layer that follows the mesopause and extends up
to 400 km in height. Except at the isothermal base, the temperature rises monotonically
with height, reaching 700°C or even higher depending on the activity of the Sun.
• The thermosphere's temperature rise is caused by the following parameters:
• The large dilution of air in these heights.
• The non-existence of molecules with three bonds.
• The presence of Sun radiation at wave lengths smaller than
1,750
• The energy which is released from exothermic chemical
reactions.
o
A

10. Exosphere • The atmosphere becomes isothermal immediately after the thermopause, and its
upper layer is known as the exosphere. The exosphere's base ranges between 400
and 500 km and is heavily influenced by the Sun's activity.
• In the exosphere, the mean free path of molecules (the distance a molecule travels
freely before colliding with another molecule) is very large (close to 1.6 km on
average). The neutral gaseous molecules can escape the gravitational field of the
Earth at these altitudes due to their high thermal conductivity.
Ionosphere • The ionosphere is the atmospheric region where partial ionisation of atmospheric
constituents occurs due to solar radiation. It stretches from 60 km up to 300 km in
height, where the density of charged particles is greatest.
• These layers play a major role in radio communications.
Magnetosphere • The magnetosphere is the atmospheric region in which ion movement is affected by
the Earth's magnetic field and extends from 1,000 km to a height close to 10 radii of
Earth's height at its illuminated part, known as the magnetopause.

11. Variation of Pressure with Height in the Atmosphere
Assuming a volume element of the atmosphere of horizontal area dA between heights of, z and z +dz.
The pressures exerted on the top and bottom faces are p(z+ dz) and p(z), respectively.
The force balance on the volume:
Force acting on the mass of air
due to gravity
Dividing by dz and letting
dz→0 produce
From the ideal-gas law, we obtain
mass density
where H(z) =RT(z)/Mairg is a characteristic length scale for decrease of pressure
with height also known as pressure scale height.
Temperature is taken constant
to get this simplified solution

12. Transfer of the atmospheric pressure at different locations (A, B, C, D) to the
mean sea level pressure
Vertical form of the pressure gradient systems

13. Dry vertical temperature lapse rate
since, 𝑐𝑣 is the thermal capacity at constant volume per unit mass
Ideal gas law is rewritten like this
First law of Thermodynamics

14. Wet vertical temperature lapse rate
When the air contains water vapor, the thermal capacity, 𝑐𝑣 of air has to be corrected. If 𝑤𝑣 is the ratio of the mass of
water vapor to the mass of dry air in a specific air volume, then the new thermal capacity coefficient, 𝑐𝑝
′
is given by the
expression,
∆𝐻𝑣 is the heat of vapour sublimition

15. The relation of the temperature versus height for an
air volume for (a) stable and (b) unstable conditions

16. Temperature inversion
• There are times when the air temperature in the lower troposphere increases rather than decreases with height. This
is known as temperature inversion.
• The inversion layer is the layer within which this phenomenon occurs. This layer is distinguished by the height of the
inversion base as well as its own height.
Schematic representation of the temperature inversion

17. Temperature inversion
Surface inversions Subsidence inversions Frontal inversions
These inversions occur as a result of the cooling
of the Earth's surface during the night. It is well
known that during the night, the Earth's surface
emits large wave length radiation (Earth's
radiation) to the atmosphere, which cools it.
The descending movement of cold air masses
from the upper atmosphere to the Earth's
surface causes subsidence inversions. The air
is compressed and heated adiabatically
during this descending movement, resulting
in a decrease in relative humidity.
Frontal inversions occur when a transport of
warm air masses occurs at a specific height in
the lower troposphere, overriding a cold air
layer that extends to the Earth's surface.
Close to the Earth's surface, air molecules
transport heat via conduction, resulting in cooling
of the lower layers of air. Cooling is observed at
low heights relative to the Earth's surface due to
the low thermal conductivity of air.
The upper layer of the air mass is warmer
than the lower layer after it has descended.
The above mechanism produces an elevated
temperature inversion known as a
subsidence inversion, which has a similar
structure to a surface inversion.
Frontal inversions at weather fronts are one
of the most common types of inversions of
this type.
Surface inversions are also known as radiation
inversions. These inversions are more intense
during the winter because the nights are longer.
In contrast to surface inversions, which last
only a few hours, subsidence inversions can
last several days or even longer.
These inversions occur as a result of
horizontal transport of warm air above a
colder air layer (warm front) as well as
horizontal transport of cold air beneath a
warm layer (cold front).
It is also possible for a surface inversion to form
during the day, particularly over snow-covered
areas. In these cases, the air masses in contact
with the snow-covered surfaces generate a lot of
heat to melt the snow. As a result, the lower
layers of air become colder than the upper layers,
favouring the formation of temperature
inversions.
For this reason the subsidence inversions are
related to air pollution episodes.
Frontal inversions have implications for air
pollution in the case of warm fronts because
warm fronts move slowly and have a small
gradient of their frontal area with the Earth's
surface, preventing pollutants from being
transported vertically.

18. Photochemical smog
Photochemical smog is the chemical reaction of sunlight, nitrogen oxides and volatile organic compounds in the
atmosphere, which leaves airborne particles and ground-level ozone.
Typical city skyline with photochemical smog

19. Features
• Photochemical smog is composed of primary and
secondary pollutants.
• Primary pollutants, which include nitrogen oxides
and volatile organic compounds, are introduced
into the atmosphere via vehicular emissions and
industrial processes.
• Secondary pollutants, like ozone, result from the
reaction of primary pollutants with ultraviolet
light.
• Photochemical smog is most common in sunny
and dry cities, like Los Angeles.
• Smog has a variety of negative health impacts.

21. Cause
• Nitrogen Dioxide ( 𝑁𝑂2 ) from vehicle exhaust, is photolyzed by
ultraviolet (UV) radiation ( hν ) from the sun and decomposes
into Nitrogen Oxide (𝑁𝑂 and an oxygen radical);
𝑁𝑂2+hν → 𝑁𝑂 + 𝑂
• The oxygen radical then reacts with an atmospheric oxygen
molecule to create ozone (𝑂3);
𝑂 + 𝑂2 → 𝑂3
• Under normal conditions, 𝑂3 reacts with 𝑁𝑂, to produce 𝑁𝑂2 and
an oxygen molecule:
𝑂3 + 𝑁𝑂 → 𝑂2 + 𝑁𝑂2
This is a continual cycle that leads only to a temporary increase in net
ozone production. To create photochemical smog, the process must
include Volatile organic compounds (VOC's).
(2)
(3)
(1)

22. • VOC's react with hydroxide in the atmosphere to create water and a reactive VOC molecule;
Cause
RH + OH → R + 𝐻2
• The reactive VOC can then bind with an oxygen molecule to create an oxidized VOC;
R + 𝑂2 → R𝑂2
• The oxidized VOC can now bond with the nitrogen oxide produced in the earlier set of equations to form
nitrogen dioxide and a reactive VOC molecule;
R𝑂2+ NO →𝑅𝑂− + NO
(4)
(5)
(6)
Nitrogen oxide, produced in equation 1, is oxidized in equation 6 without the destruction of any ozone.
This means that in the presence of VOCs, equation 3 is essentially eliminated, leading to a large and
rapid build-up in the photochemical smog in the lower atmosphere.

23. Effects on human health
• Birth abnormalities and low birth weight are strongly associated with smog. Babies born to women who are
exposed to pollution are more likely to develop birth abnormalities. Anencephaly, or the underdevelopment or
absence of all or part of the brain, and spinal column anomalies are two features of the disorder known as
spina bifida. According to recent studies, exposure to smog particulate matter at levels as low as 5 g can
increase the chance of very low birth weights.
• Long-lasting, dense haze prevents UV rays from reaching the earth's surface. As a result of the bone marrow's
decreased ability to process calcium and phosphorus, there is a low generation of vitamin D, which causes
rickets.
• Coughing and irritation of the eyes, chest, nose and throat because
of high ozone level. Asthma conditions are severely worsened by
smog and can trigger asthma attacks.
• Bronchitis, pneumonia, and emphysema are some of the lung
conditions linked to the effects of smog as it damages the lining of
the lungs. Smog also makes it difficult for people to breathe
properly.

24. Implications for Plants and Animals
1. Smog inhibits the growth of plants and can lead to extensive damage to
crops, trees, and vegetation.
2. When crops and vegetables such as wheat, soybeans, tomatoes, peanuts,
cotton and kales are exposed to smog, it interferes with their ability to
fight infections thus increasing susceptibility to diseases.
3. The smog’s impact of altering the natural environment makes it difficult
for animals to adapt or survive in such toxic conditions, which can kill
countless animal species or make them susceptible to illness.
4. Photochemical smog caused when nitrogen oxides react in the presence
of sunlight, is established to destroy plant life and irritate sensitive tissues
of both plants and animals.
Ozone injury to soybean foliage
Acute sulfur dioxide injury to raspberry

25. Lecture #03

26. Atmospheric circulation
The equations of movement for a compressible fluid in a gravimetric field are expressed as
Energy equation for compressible fluid
= produced heat per unit volume
= thermal diffusion
Continuity equation for the compressible fluid can be written as
For static atmosphere

27. Upon integration
Therefore from the above results it can be concluded that when the atmosphere
is static it can be written that
Final form of the equation of motion
express the variations of the quantities due
to the motion
Final form of the equation of energy
is the potential temperature

28. Gaseous constituents of atmosphere

29. Atmospheric sulphur compounds

30. Global sulphur emission estimates [Tg(S)yr−1]
At present, anthropogenic (human activity)
emissions account for about 75% of total
sulphur emissions, and 90% of the
anthropogenic emissions occur in the
Northern Hemisphere.
Global SO2 emissions from fuel combustion and chemical
processes (Gg SO2 yr-1).

31. Atmospheric nitrogen containing compounds

32. Global N2O Budget (TgNyr–1) for 2006 Global Tropospheric Nox Emissions (TgNyr–1)
Estimated Annual Global Ammonia Emissions

33. Atmospheric Organic Species

34. Schematic representation of the chemical reactions and processes associated with the
particulate matter

35. Global Emission Estimates for Major Aerosol Classes

36. Physico-chemical processes related to the aerosol particle size

37. Chemical mass closure of PM10 aerosols at the Birkenes station in Norway during 2004

38. Chemical reactions with the presence of solar radiation in the atmosphere

39. Spatial and temporal scales of atmospheric processes
Microscale Mesoscale Synoptic Scale Global Scale

40. Lecture 4

41. Atmospheric dispersion
• The Gaussian plume model is a popular mathematical model that is typically applied to point source emitters,
such as coal-burning electricity-producing plants to determine the pollution.
• The model attributes the change in the plume shape and spread to meteorological conditions.
Assumptions:
– Steady-state conditions (constant source emission strength).
– Wind speed, direction and diffusion characteristics of the
plume are constant.
– Mass transfer due to bulk motion in the x-direction far
dominates the contribution due to mass diffusion.
– Conservation of mass, i.e. no chemical transformations take
place.
– Wind speeds are >1 m/sec.

42. Graphical description of plume
Thermal stage:
• Mixing due to initial turbulence.
• Moderate ascending and planar shape.
• Application of a linear thermal model.
• Plume reaches its maximum height at this stage.
Intermediate stage:
• Dominance of the atmospheric turbulence.
• Breaking of the plume into small compartments.
• A stepwise increase of the plume diameter.
Diffusion stage:
• Dominance of the atmospheric turbulence diffusion.
• Plume formation– even larger diffusion.
• Relatively slow development.

43. Richardson's number is the ratio of stability s to turbulence production and is both an atmospheric stability
parameter and a turbulence occurrence parameter.
Potential temperature

44. Model derivation:
( )
( ) ( )
( )
x
x
x x
x dx
x
x dx x
D C
N dydz
x
D C D C
N dydz dydz dx
x x x
D C
N N dydz dxdydz
x x



 

   
  
    
 
  
 
 
  
  
   
 
 
 
 
( )
CUdydz
CUdydz CUdydz dx
x
CUdydzdx
x
C
dxdydz dxdydz
t


 


 




Rate in (bulk motion)
Rate out (bulk motion)
Net rate (bulk motion)
Rate of change within

45. Where;
x = along- wind coordinate measured in wind direction from the source
y = cross-wind coordinate direction
z = vertical coordinate measured from the ground
C(x,y,z) = mean concentration of diffusing substance at a point (x,y,z) [kg/m3
]
Dy, Dz = mass diffusivity in the direction of the y- and z- axes [m2/s]
U = mean wind velocity along the x-axis [m/s]
Time rate of change and advection of the cloud by the mean
wind
=
=
Turbulent diffusion of material relative to the center of the pollutant
cloud ( the cloud will expand over time due to these terms)

46. 2 2
2 2
C C C
U Dy Dz
x y z
   
  
 
 
   
 
  
     
Where,
After simplification
2 2
1
exp
4
y z U
C Kx
Dy Dz x

 
 
   
 
  
 
 
   
   
 
 
 
The rate of transfer of pollutant through any vertical plane downwind is equal to the emission rate of the source,
Q UCdydz
 
2 2
1
exp
4
y z U
Q KUx dydz
Dy Dz x
 

 
 
 
   
 
  
 
 
   
   
 
 
 
 

47. 2 2
1
exp
4
y z U
Q KUx dydz
Dy Dz x
 

 
 
 
   
 
  
 
 
   
   
 
 
 
 
After integrating,
1/2
4 ( )
Q
K
DyDz

 Q is the strength of the emission source, mass emitted per unit
time.
2 2
1/2
( , , ) exp
4 ( ) 4
Q y z U
C x y z
DyDz Dy Dz x

 
 
  
 
 
 
 
𝐶(𝑥, 𝑦, 𝑧) =
𝑄
2𝜋𝑈𝜎𝑦𝜎𝑧
exp −
𝑦2
2𝜎𝑦
2 exp
−(𝑧 − 𝐻)2
2𝜎𝑧
2
+ exp
−(𝑧 + 𝐻)2
2𝜎𝑧
2
Where;
Q = contaminant emission rate [mass/s],
σx = lateral dispersion coefficient function [m],
σy = vertical dispersion coefficient function [m],
U = mean wind velocity in downwind direction [m/s],
H = effective stack height [m].

49. 2 2
( 0) exp 0.5 exp 0.5
2
z
y z y z
Q y H
C
U
    

   
   
   
    
 
   
 
 
 
   
   
 
2 2
2 2
( , , ) exp
y z
y z
Q y z
C x y z
u  
 
 
 
  
 
 
 
 
 
 
2
( 0, 0) exp 0.5
2
z y
y z z
Q H
C
U
   
 
 
 
 
  
 
 
 
 
 
Ground level concentration
If the emission source is at ground level with no effective plume rise then,
The point of maximum concentration occur along plume center line,

50. Ozone chemistry
• About 90% of the atmosphere’s ozone is found in the stratosphere, residing in what is commonly referred to
as the ozone layer.
• At the peak of the ozone layer the O3 mixing ratio is about 12ppm.
• Ozone in the stratosphere is created spontaneously when oxygen undergoes photolytic oxidation. The
resulting two oxygen atoms each combine with an additional O2 molecule to form two ozone molecules.
Consequently, the total process changes three O2 molecules into two O3 molecules.
• The O3 molecules generated interact with other natural and man-made molecules in the stratosphere; the
equilibrium between O3 creation and destruction results in a steady-state abundance of O3.

51. Formation
• Ozone formation occurs in the stratosphere above ∼30 km
altitude, when molecular oxygen is slowly split apart by solar
UV light with wavelengths less than 242 nm;
• Where reaction 3’ leads to excited states of both O and O2[O2(1Δ)]. is quenched to ground-state
atomic oxygen by collision with N2 or O2.
1
O( D)
Rate coefficients, Mean life time of ,
1
O( D)

52. • The rate equations for [O] and [O3] in the Chapman mechanism are;
Formation
Odd-oxygen family
Zonally averaged ozone concentration (in units of 1012
molecules/cm3) as a function of altitude

53. Influence of CFC on ozone layer
Specifically chlorofluorocarbons (such as CFCl3 and CF2Cl2) are
destroyed in the stratosphere from ultraviolet radiation with the
production of chlorine atoms,
First there is a photo dissociation of CFCs with the formation of a
ClONO2 molecule,
With the presence of polar stratospheric clouds, there are
the following reactions,
In total,

54. Cause of Global warming
Global average annual surface temperature as measured from
a meteorological network from 1880 until today. The grey line
shows the annual value and the black line the average 5 years
value
1. Emission of gaseous chemical from the factories have
been increasing since the industrial revolution.
2. Rapid deforestation.
3. Excess burning of fossil fuels (transportation, power
generation, etc.), thereby releasing carbon di oxide,
carbon monoxide.
4. Animal farming is responsible for a large amount of
methane emission.
Global warming

55. Consequences of Global warming
• The temperature of the Earth will generally rise in comparison to past times, albeit not everywhere will
experience this warming.
• As a result of global warming, Greenland's and the Atlantic's glaciers and ice sheets will melt, raising the sea level
and raising the risk of calamities like tsunamis. The economy will be impacted by a rise in sea level, particularly in
low-lying coastal regions and islands where soil erosion is unavoidable.
• Crop growth is twice as fast as usual due to the elevated CO2 content in the atmosphere. The typical level of
agricultural production may be affected by the altering of the climatic pattern, which may also modify the regions
where crops grow more quickly and effectively.
• The greenhouse effect plays a significant role in keeping the Earth warmer because it prevents part of the planet's
heat from escaping the atmosphere and into space, . The average global temperature of the planet would actually
be much colder without the greenhouse effect, making life on the planet impossible.

56. Greenhouse gases:
1. Water vapor (H2O)
2. Carbon dioxide (CO2)
3. Methane (CH4)
4. Nitrous oxide (N2O)
5. Ozone (O3)
6. Chlorofluorocarbons
(CFCs)

57. Greenhouse effect
Considering a one-layer atmosphere that is
transparent to incoming shortwave (SW) radiation
but completely absorbing of longwave (LW)
radiation. We also assume a LW emissivity ε=1.
Considering one-layer atmosphere that is transparent to
SW radiation and partially absorbing of LW radiation. Let
ε be the fraction of LW absorption by the atmosphere,
0<ε<1.
a e s
T T T
 

58. Greenhouse effect
We can extend the earlier study to account for two absorbing layers as shown below
Assuming 100% LW absorptivity
After combining above equations
Assuming partial LW absorptivity

59. Atmospheric concentration of CO2 as measured at a glacier from the
station Siple (Adapted from Neftel et al., 1985). The above data
showed that the atmospheric concentration of CO2 during 1750 was
280 ppmv (parts per million by volume) and is increased by 22.5% to
345 ppmv during 1984.
Variation of the CO2 concentration and the
Earth’s temperature the last 160 years

60. Air pollutants
• A chemical in the air that can be harmful to both people and the environment is referred to as an air
pollutant.
• The three different types of pollutants are solid particles, liquid droplets, and gases. These pollutants may
either be anthropogenic (man made) or natural.
Based on the source, air pollutants can be further categorized to
Primary pollutants are substances that are released as a direct result of a process, such as volcanic ash, carbon
monoxide gas from automobile exhaust, or sulphur dioxide from factories.
Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants react or
interact. An important example of a secondary pollutant is ground level ozone is one of the many secondary
pollutants that causes photochemical smog.

61. Primary pollutants
Sulphur Oxides: from volcanic eruptions, industrial emission and Sulphur containing
fuel.
Nitrogen oxides: from high temperature combustion
Carbon monoxide: from incomplete combustion of wood, natural gas, coal, etc.
Carbon dioxide: from combustion fossil fuel.
Volatile organic compounds: methane VOCs from animals and non methane VOCs
from industries.
Particulate matter: from volcanic eruptions, burning unrefined fossil fuel, power
plants, industrial processes, etc.
Ammonia, toxic metals like lead, copper, cadmium, chlorofluorocarbons,
radioactive pollutants
Secondary pollutants
Particulate matter: from gaseous primary pollutants and compounds in
photochemical smog.
Ground level ozone (O3): formed from NOx and VOCs.
Peroxyacetyl nitrate (PAN): from NOx and VOCs
Air pollutants

62. Sources of air pollution
Anthropogenic
sources
Stationary Sources: smoke stacks of power plants, manufacturing facilities
(factories) and waste incinerators, as well as furnaces and other types of fuel-
burning heating devices.
Mobile Sources: motor vehicles, marine vessels, aircraft and the effect of sound etc.
Controlled burning of forests and crops for induced germination of desirable trees.
Fumes from paint, hair spray, varnish, aerosol sprays and other solvents.
Waste deposition in landfills, which generate methane.
Military, such as nuclear weapons, toxic gases, germ warfare and rocketry.
Natural sources
Dust from natural sources, usually large areas of land with little or no vegetation.
Methane, emitted by the digestion of food by animals, for example cattle.
Radon gas from radioactive decay within the Earth’s crust.
Smoke and carbon monoxide from wildfires.
Volcanic activity, which produce sulphur, chlorine, and ash particulates.

63. Pollutant Harmful effects on human health
Carbon monoxide Affects the respiratory activity as haemoglobin has more affinity for CO than for oxygen. Thus, CO combines with HB
and thus reduces the oxygen-carrying capacity of blood. This results in blurred vision, headache, unconsciousness
and death due to asphyxiation (lack of oxygen)
Carbon dioxide Causes global warming.
Sulphur dioxide Respiratory problems, severe headache, reduced productivity of plants, yellowing and reduced storage time for
paper, yellowing and damage to limestone and marble, damage to leather, increased rate of corrosion of iron, steel,
zinc and aluminium.
Hydrocarbons Poly nuclear Aromatic
Compounds(PAC) and Poly-nuclear Aromatic
Hydrocarbons(PAH)
Carcinogenic (may cause leukaemia).
Chloro-fluoro carbons (CFCs) Destroy ozone layer which then permits harmful UV rays to enter the atmosphere. The ozone layer protects the
earth from the ultraviolet rays sent down by the sun. If the ozone layer is depleted by human action, the effects on
the planet could be catastrophic.
Nitrogen Oxides Forms photochemical smog, at higher concentrations causes leaf damage or affects the photosynthetic activities of
plants and causes respiratory problems in mammals.
Particulate matter Lead halides Toxic effect in man
Asbestos particles A cancerous disease of the lungs.
Silicon dioxide Silicosis, a cancerous disease.
Mercury Brain & kidney damage.
Peroxyacetyl nitrate Causes silvering of lower surface of leaf, damage to young and more sensitive leaves and suppressed growth.
Fluorides cause necrosis of leaf-tip while ethylene results in epinasty, leaf abscission and dropping of flowers.

64. Particle size range and measurement criteria for aerosols

65. Air pollution control
The following techniques are frequently employed by industrial or transportation equipment as pollution control
methods. Prior to being released into the atmosphere, they can either eliminate impurities or remove them from an
exhaust stream.
Particulate control:
• Mechanical collectors such as dust cyclones, multi-cyclones utilizes cyclonic
separation which is a method of removing particulates from an air, gas or
water stream, without the use of filters, through vortex separation.
Rotational effects and gravity are used to separate mixtures of solids and
fluids.
• Within a cylindrical or conical container referred to as a cyclone, a high speed
rotating (air) flow is created. Before leaving the cyclone in a straight stream
through the centre of the cyclone and out the top, air moves in a spiral
pattern from the top (wide end) to the bottom (narrow end) of the cyclone.
• Larger (denser) particles can't follow the stream's tight curve because of
their greater inertia. Instead, they hit the outside wall and fall to the bottom
of the cyclone, where they may be removed.

66. Electrostatic precipitators:
• A particulate collecting device called an electrostatic
precipitator (ESP) or electrostatic air cleaner uses
the force of an induced electrostatic charge to
remove particles from a moving gas, such as air.
• Electrostatic precipitators are extremely effective
filtering tools that just slightly restrict gas flow while
effectively removing tiny particulates like smoke and
dust from the air stream.
• An ESP is particularly efficient at using energy since
it solely applies it to the particulate matter being
collected, as opposed to wet scrubbers, which also
apply energy to the flowing fluid medium (in the
form of electricity).

67. Particulate scrubbers:
• Different equipment that removes pollutants from furnace flue gas
or other gas streams is referred to as "wet scrubbers." In a wet
scrubber, the polluted gas stream is forced through a pool of liquid,
sprayed with the liquid, or exposed to another means of contact to
the liquid in order to remove the pollutants.
• The characteristics of the industrial process and the types of air
pollutants involved determine the design of wet scrubbers or any
other air pollution control device. The qualities of the inlet gas and
any dust particles are of utmost significance.
• Scrubbers can be constructed to gather gaseous or particle
pollution. By encapsulating them in liquid droplets, wet scrubbers
eliminate dust particles. By dissolving or absorbing the polluting
gases into the liquid, wet scrubbers remove them from the air.
• By using a different device known as a mist eliminator or
entrainment separator, any droplets in the scrubber's incoming gas
must be removed from the outlet gas stream (these terms are
interchangeable). Additionally, the resulting cleaning liquid needs to
be cleaned before it can be released into the environment or used
again in the plant.