Air Pollution and Air Pollution Control Air...Air Pollution Accumulation of substances in the...

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1 Air Pollution and Air Pollution Control Air Troposphere “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

Transcript of Air Pollution and Air Pollution Control Air...Air Pollution Accumulation of substances in the...

Page 1: Air Pollution and Air Pollution Control Air...Air Pollution Accumulation of substances in the atmosphere that can cause harmful health effects to living things or can negatively affect

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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