Air Pollution and Air Pollution Control Air...Air Pollution Accumulation of substances in the...
Transcript of Air Pollution and Air Pollution Control Air...Air Pollution Accumulation of substances in the...
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Air Pollution and Air Pollution
Control
AirTroposphere
• “ambient air” nearest to Earth's surface
• weather occurs here
• Properties:
– approximately 80% of the atmosphere's mass
– 99% of its water vapor and aerosols
– average depth of approximately 17 km (11 mi) in the middle latitudes
– deeper in the tropics, up to 20 km (12 mi)
Air
• Troposphere
– Ozone here is considered a pollutant
• Stratosphere
– situated between about 10 km (6 mi) and 50 km (30 mi) altitude
– location of protective ozone layer: absorbs high energy UV B and UV C energy waves from the Sun
• Three more layers above
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The Earth’s Atmosphere
• Earth's Atmosphere Has Changed
Dramatically since the Time it was Formed
– some changes the result of chemical and
physical characteristics of the earth and the
gases
The Earth’s Atmosphere
Early Earth
• no oxygen at that time
• Instead high in CO2, H2O vapor, and probably NH3, H2 and CH4
Now
• considerable reduction in CO2; significant increase in O2
If true,
• Where did the “C” of CO2
go?
Current Composition of
Atmosphere
78.08% N2
20.95% O2
0.9% Ar
0.036% CO2
• trace amounts of gases, vapors, particulates
– naturally occurring: Ne, He, Kr, Xe, H2, CH4, O3, N2O
these have remained relatively constant for at least
several hundred million years
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Current Composition of
Atmosphere
whatever humans emit considered trace
amounts
– example CFC = 0.000000002%
But still can have a significant impact
Atmosphere Bombarded by Solar
Radiation
Some is reflected
back to space
by stratospheric
ozone or clouds
while others
penetrate
Air Pollutants
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Air Pollution
Accumulation of substances in the
atmosphere that can cause harmful health
effects to living things or can negatively
affect the public welfare
Matter cannot be created or destroyed, it
only changes form: Pollutants just don’t
disappear but they may change form
Fate of Air Pollutants in the
Environment
• Dispersion
• Deposition
• Degradation
• Transfer to other compartments
Effects of Air Pollutants
•Wildlife health including forests
•Impact on agriculture
•Buildings and other property
•Visibility and navigation
•Human health effects:
•Irritation of the respiratory passages including nose, throat,
trachea and bronchii
•Eye irritation
•Increased susceptibility to the common cold
•Neural disorders (from toxics like lead)
•Other toxic effects
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Air Pollution Sources
• Anthropogenic
• Geogenic
• Biogenic
Anthropogenic Sources
• Stationary Sources
– Stack emissions
– Fugitive emissions
– Major stationary sources
– Small sources
• Mobile Sources
• Accidental spills
Air Pollutant Types and Sources
Energy-
related?
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(ozone related)
Other Sources
• Geogenic
– volcanoes
– dust storms
Other Sources
• Biogenic
– decomposition gases
– organic molecules released from plants and
animals
– cow gas?
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Progress Being Made?
Other Pollutants
Hazardous Air Pollutants (HAPS)
• asbestos, benzene, mercury, vinyl
chloride, radionuclides, numerous others
– Each has its own sources and effects
– Toxicity/carcinogenicity, persistence, and
bioaccumulation the key issues
General Air Pollution Control
Strategies
• Source Shutdown
• Source Location
• Fuel Substitution and Process Changes
– Very successful with autos
• Correct Operation and Maintenance, Efficiency
• Emissions Trading
• ‘End of Pipe’ Pollution Control Technologies
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‘End of Pipe’ controls
• Consider only after other options are
exhausted?
• Selection heavily regulated by
environmental statutes
Pollution Control Technologies
• Form of substance dictates control
technology used
– Gases
– Particulates
• Physical and chemical properties of the
pollutant also dictate which particular
methods will be effective
Control Technologies
• Various levels of control technologies exist
• Best Available Control Technology (BACT)
• Maximum Achievable Control Technology (MACT)
• Ultimately, choice depends on:– Form of contaminant
– Regulatory requirements for a particular industry
– Quantity generated
– Installation costs
– Maintenance and operational costs
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Characteristics of Pollutants
• Physical state
• Size (µm)
• Size distribution
• Density
• Reactivity
Characteristics of Carrier Gases
• Flow rate (cfm)
• Moisture content
• Temperature
• Flammability
Particulate Emissions Control
Common control devices include
• Settling chambers
• Cyclones
• Wet scrubbers
• Electrostatic precipitators
• Fabric filters (baghouse filters)
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Settling Chambers
Cyclones
Wet Scrubbers
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Electrostatic Precipitator
Baghouse Filters
Gaseous Emissions Control
Four Major Techniques
• Adsorption
• Absorption
• Condensation
• Combustion
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Adsorption
• Attachment of
gas/vapor to a solid
Absorption
• Dissolving gaseous
pollutants in a liquid
Condensation
• Removal of gas or vapor by condensing it
into liquid form
• Uses changes in temperature and/or
pressure
• The pollutant(s) must be condensable at
achievable temperature
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Combustion