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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.
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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!)
Nitrogen(78.08% ), Oxygen (20.946%) 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 Argon (0.9340% ) Carbon dioxide (0.039% )
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
Pressure & Density Gravity pulls gases toward earth's surface, and the whole column of gases exerts a pressure of 1000 hPa at sea level, 1013.25 mb or 29.92 in.Hg.
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 Layers • 8 layers are defined by constant trends in average air temperature (which changes with pressure and radiation), where the outer exosphere is not shown. • Troposphere • Tropopause • Stratosphere • Stratopause • Mesosphere • Mesopause • Thermosphere • Exosphere
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 -560C ) –ve lapse rate • Weather and climate layer, very turbulent, mixing of air • Most of atmosphere’s mass(80%) ; all of its water
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 km • Moderate latitude: 12 to 50 km • Equator: 18 to 50 km Very stable in nature Temperature range: -56 to -2 0C i.e. lapse rate is +veWhy?
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 km • Moderate latitude: 12 to 50 km • Equator: 18 to 50 km Very stable in nature Temperature range: -56 to -2 0C i.e. lapse rate is +ve • Ozone layer ( absorb UV rays 190nm-380nm )
Upper region of stratosphere is separated by the lower region of the mesosphere in a narrow range called the Stratopause • 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 mesosphere is separated by the lower region of the thermosphere in a narrow range called the Mesopause 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.
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
Air Pollution and Controll Atmospheric Composition: Troposphere, Stratosphere, Mesosphere, Thermosphere, Tropopause and Mesopause. 1LEnergy balance: Conductive and Convective heat transfer, radiation heat transfer, simple global temperature model [Earth as a black body, earth as albedo], 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. Earth’s heat budget. 1LLapse rate: Ambient lapse rate, adiabatic lapse rate, atmospheric stability, temperature inversion (radiation inversion). 2LAtmospheric dispersion: Maximum mixing depth, ventilation coefficient, effective stack height, smokestack plumes and Gaussian plume model. 2LDefinition 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. 1LStandards 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
References/Books Masters, G. M., “Introduction to Environmental Engineering and Science”, Prentice-Hall of India Pvt. Ltd., 1991. De, A. K., “Environmental Chemistry”, New Age International. Dasmahapatra , Gourkrishna “Environment & Ecology” Vikas Publishing House Pvt. Ltd. Mandal , T “Environment and Ecology” DhanpatRai Publishing Company
