Lecture 1 Atmospheric Composition

8/2/2019 Lecture 1 Atmospheric Composition

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Air Pollution & Control


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Thickness of Atmosphere

The atmosphere is a very thin (relatively) layer

of gas over the surface of the Earth

Earths radius ~ 6400km

Atmospheric thickness ~ 100km

(If you travel 100km vertically youd be inspace!)


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Atmospheric Structureand Composition


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Atmosphericcomponents

Major Minor Trace

Nitrogen(78.08% ),Oxygen (20.946%) Argon (0.9340% )Carbon dioxide

(0.039% )

Ne (0.001818%)He (0.000524%)CH4 (0.000179%)Kr (0.000114%)H2 (0.000055%)N2O (0.00003%)

CO (0.00001%)Xe (0.000009%)O3(0 to 710

6%)NO2 , I2 , NH3 ,H2S


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Composition of the Air

Uniform gases

Nitrogen (N2) , Oxygen (O2) ,Argon (Ar), trace gases (Neon(Ne), Helium(He), Methane (CH4), etc.)

Variable gases

Water Vapor (H2O), O3, CO2


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The Atmospheric Layers


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Activities observed in atmospheric layers


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Pressure & Density

Gravity pulls gases

toward earth's

surface, and thewhole column of

gases exerts a

pressure of 1000

hPa at sea level,

1013.25 mb or 29.92

in.Hg.


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Beautiful view of kanchanjangha


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Lapse Rate

The rate at which air temperature decreases

with height.

The standard (average) lapse rate in the

lower atmosphere is about 6.5C per 1 km or

3.6F per 1000 ft.


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Lapse Rate

The rate at which air temperature decreases

with height.

The standard (average) lapse rate in the

lower atmosphere is about 6.5C per 1 km or

3.6F per 1000 ft.

Positive lapse rate & negative lapse rate


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Atmospheric Layers

8 layers are defined byconstant trends in average air

temperature (which changeswith pressure and radiation),where the outer exosphere isnot shown.

1. Troposphere

2. Tropopause3. Stratosphere4. Stratopause5. Mesosphere6. Mesopause7. Thermosphere

8. Exosphere


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Vertical Structure of Atmosphere

Troposphere (surface to 10-18 km)

Upper boundary varies from about 10 km (poles in

winter) to about 18 km (tropics)

Polar latitude: surface to 10 km

Moderate latitude: surface to 12 km

Equator: surface to 18 km

Temperature range: 15 to -560

C (30 to -56

0

C )velapse rate

Weather and climate layer, very turbulent, mixing of air

Most of atmospheres mass(80%) ; all of its water


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Stratosphere (10-18 km to 50 km)

Polar latitude: 10 to 50 km

Moderate latitude: 12 to 50 km

Equator: 18 to 50 km

Very stable in natureTemperature range: -56 to -2 0C i.e.

lapse rate is +ve Why?

Upper region of troposphere is separated by the lower

region of the strtosphere in a narrow range called theTropopause


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Stratosphere (10-18 km to 50 km)

Polar latitude: 10 to 50 km

Moderate latitude: 12 to 50 km

Equator: 18 to 50 km

Very stable in natureTemperature range: -56 to -2 0C i.e. lapse rate is +ve

Ozone layer ( absorb UV rays 190nm-380nm )

Upper region of troposphere is separated by the lower

region of the strtosphere in a narrow range called theTropopause


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Mesosphere (50 km to 85 km)

Temperature range: -2 to -920

CConcentration of ozone is very low

Need oxygen to live in this region

Upper region of stratosphere is separated by thelower region of the mesosphere in a narrow range

called the Stratopause


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Thermosphere/ Ionosphere (85 km to 500 km)

Temperature range: -92 to 12000

CHot layer oxygen molecules absorb energy

from solar Rays warming the air. Very few

atoms and molecules in this Region.

Upper region of mesosphere is separated by the lowerregion of the thermosphere in a narrow range called theMesopause


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Magnetoosphere/ Exosphere (500 km to 2000 km)

Temperature range: >1200 0C

Air less, probably contains hydrohen gas in

ionized state

Very little is known about this layer


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Characteristics of the various

regions of atmosphere

Region

Altitude

( in km)

Temperature

(0C)

Major

chemical

species

Troposphere 0 to 18 15 to 56 N2, O2, CO2,

H2O (vapour)

Stratosphere 18 to 50 56 to 2 O3, O2, O

Mesosphere 50 to 85 2 to 92 O2, NO

Thermosphere 85 to 500 92 to 1200 O2+, NO+, O+

Exosphere 500 to 2000 1200 H2+


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Atmospheric Composition: Troposphere, Stratosphere, Mesosphere,

Thermosphere, Tropopause and Mesopause. 1L

Energy balance: Conductive and Convective heat transfer, radiation heat

transfer, simple global temperature model [Earth as a black body, earth asalbedo], Problems. 1LGreen house effects: Definition, impact of greenhouse gases on the global

climate and consequently on sea water level, agriculture and marine food.

Global warming and its consequence, Control of Global warming. Earths heat

budget. 1L

Lapse rate: Ambient lapse rate, adiabatic lapse rate, atmospheric stability,temperature inversion (radiation inversion). 2L

Atmospheric dispersion: Maximum mixing depth, ventilation coefficient,

effective stack height, smokestack plumes and Gaussian plume model. 2L

Definition of pollutants and contaminants, Primary and secondary

pollutants: emission standard, criteria pollutant. Sources and effect of different

air pollutants- Suspended particulate matter, oxides of carbon, oxides ofnitrogen, oxides of sulphur, particulate, PAN. 2L

Smog, Photochemical smog and London smog. Depletion Ozone layer: CFC,

destruction of ozone layer by CFC, impact of other green house gases, effect of

ozone modification. 1L

Standards and control measures: Industrial, commercial and residential airquality standard, control measure (ESP. cyclone separator, bag house, catalytic

converter, scrubber (ventury), Statement with brief reference). 1L

Air Pollution and Controll


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References/Books

1. Masters, G. M., Introduction to EnvironmentalEngineering and Science, Prentice-Hall of India Pvt.Ltd., 1991.

2. De, A. K., Environmental Chemistry, New AgeInternational.

3. Dasmahapatra , Gourkrishna Environment & Ecology

Vikas Publishing House Pvt. Ltd.

4. Mandal , T Environment and Ecology Dhanpat RaiPublishing Company

Lecture 1 Atmospheric Composition

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