Air Pollution & Control

Thickness of Atmosphere

• The atmosphere is a very thin (relatively) layer of gas over the surface of the Earth

• Earth’s radius ~ 6400km• Atmospheric thickness ~ 100km• (If you travel 100km vertically you’d be in

space!)

Atmospheric Structure and Composition

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 7×10−6%) NO2 , I2 , NH3 ,H2S

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

The Atmospheric Layers

Activities observed in atmospheric layers

Pressure & DensityPressure & Density

Gravity pulls gases Gravity pulls gases toward earth's toward earth's surface, and the surface, and the whole column of whole column of gases exerts a gases exerts a pressure of 1000 pressure of 1000 hPa at sea level, hPa at sea level, 1013.25 mb or 29.92 1013.25 mb or 29.92 in.Hg.in.Hg.

Beautiful view of kanchanjangha

Lapse Rate

• The rate at which air temperature decreases with height.

• The standard (average) lapse rate in the lower atmosphere is about 6.5°C per 1 km or 3.6°F per 1000 ft.

Lapse Rate

• The rate at which air temperature decreases with height.

• The standard (average) lapse rate in the lower atmosphere is about 6.5°C per 1 km or 3.6°F per 1000 ft.

• Positive lapse rate & negative lapse rate

Atmospheric LayersAtmospheric Layers 8 layers are defined by 8 layers are defined by

constant trends in average air constant trends in average air temperature (which changes temperature (which changes with pressure and radiation), with pressure and radiation), where the outer exosphere is where the outer exosphere is not shown.not shown.

1.1. TroposphereTroposphere2.2. TropopauseTropopause3.3. StratosphereStratosphere4.4. StratopauseStratopause5.5. MesosphereMesosphere6.6. MesopauseMesopause7.7. ThermosphereThermosphere8.8. ExosphereExosphere

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 -56 0C (30 to -56 0C ) –ve lapse rate

Weather and climate layer, very turbulent, mixing of airMost of atmosphere’s mass(80%) ; all of its water

• Stratosphere (10-18 km to 50 km)Polar latitude: 10 to 50 kmModerate latitude: 12 to 50 kmEquator: 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 the Tropopause

• Stratosphere (10-18 km to 50 km)Polar latitude: 10 to 50 kmModerate latitude: 12 to 50 kmEquator: 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 the Tropopause

• Mesosphere (50 km to 85 km)

Temperature range: -2 to -92 0C Concentration of ozone is very low

Need oxygen to live in this region

Upper region of stratosphere is separated by the lower region of the mesosphere in a narrow range called the Stratopause

Thermosphere/ Ionosphere (85 km to 500 km)

Temperature range: -92 to 1200 0C “Hot 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 lower region of the thermosphere in a narrow range called the Mesopause

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

Characteristics of the various regions of atmosphere

RegionAltitude( 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+

  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 as albedo], Problems. 1L Green 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. Earth’s 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 of nitrogen, oxides of sulphur, particulate, PAN.2LSmog, 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 air quality standard, control measure (ESP. cyclone separator, bag house, catalytic converter, scrubber (ventury), Statement with brief reference). 1L

Air Pollution and Controll

References/Books

1.Masters, G. M., “Introduction to Environmental Engineering and Science”, Prentice-Hall of India Pvt. Ltd., 1991.

2.De, A. K., “Environmental Chemistry”, New Age International.

3.Dasmahapatra , Gourkrishna “Environment & Ecology” Vikas Publishing House Pvt. Ltd.

4.Mandal , T “Environment and Ecology” Dhanpat Rai Publishing Company