Website download address

1
Website download address

• Air Polution
• http//www.public.iastate.edu/sung/ce326/air.ppt

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Environmental Ethics

• Professional Ethics -
• Decisions made in the best of public interest
• Civil Engineer Code of Ethics
• Engineers shall hold paramount the safety,
  health and welfare of the public in the
  performance of their duties
• Environmental Ethics
• Decision made in the best interest of the
  environment
• - Realize that humans are but one form of life
  we share our earth with other forms of
  life
• -No diminishing shared resource or permanently
  change of environment

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Air Pollution

• Background
• Air Quality Standards
• Sources of Air Pollution
• Meteorology

• Effects of Air Pollution
• Global Issues
• Air Pollution Control Devices

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Composition of Normal Dry Air
(1969 data)
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Changes in Air Composition

• Carbon Dioxide
• 352 ppm in 1989 369 ppm in 2000 (Hawaii)
• Nitrous Oxide
• 0.304 ppm in 1985 0.314 ppm in 1999 (Tasmania,
  Australia)
• Methane
• 1.7 ppm in 1990 1.73-1.84 ppm in 1999 (Tasmania,
  Australia)

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Air Pollution Episodes
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Air Quality Standards

• Ambient Air Quality Standards
• Primary standards are designed to establish
  limits to protect public health, including the
  health of "sensitive" populations such as
  asthmatics, children, and the elderly.
• Secondary standards set limits to protect public
  welfare, including protection against decreased
  visibility and damage to animals, crops,
  vegetation, and buildings.

Page 463-464
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National Ambient Air Quality Standards
These pollutants are monitored.
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National Ambient Air Quality Standards
Page 465
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Classification of Air Pollutants

• State of matter Gases or suspended
  particulate matter
• Source of pollutants
• Natural
• Emissions from volcanic eruptions, smoke
  particles from forest fire, pollen grains, fungus
  spores, etc.
• Gaseous pollutants from natural sources include
  carbon dioxide and other gases such as hydrogen
  sulfide and hydrocarbons.
• Anthropogenic (Human-made)
• Near cities and in populated areas, more than
  90 of the volume of air pollutants is
  contributed by human activity.
• Stationary sources combustion processes,
  industrial processes, and construction and
  demolition
• Contribute approximately 40 of total air
  pollution (98 of SOx, 95 of particulates, 56
  of hydrocarbons, 53 of NOx, and 22 of CO)
• Mobile sources motor vehicles, aircraft,
  railroads, ships, handling and/or evaporation of
  gasoline
• Contribute approximately 60 of total air
  pollution (78 of CO, 47 of NOx, 44 of total
  hydrocarbons, 5 of particulates, and 2 of SOx)

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Classification of Air Pollutants

• Chemical composition
• Organic compounds hydrocarbon, aldehydes etc.
• Inorganic materials CO, CO2, SO2, NOX etc.
• Origin
• Primary pollutants
• Pollutants such as sulfur oxides, nitrogen
  oxides, and hydrocarbons, which are directly
  emitted to the atmosphere and found there in the
  same form in which they were emitted
• Secondary pollutants
• Pollutants such as ozone and peroxylacetyl
  nitrate (PAN), which are formed in the atmosphere
  by a photochemical reaction or by hydrolysis or
  oxidation

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Variation on Spatial Scale

• Small scale indoor air pollution
• We spend most of our lives indoors.
• Some pollutants (such as solvents) are present
  at higher concentration indoor than outdoor.
• Intermediate scale localized air pollution
• Air pollution episodes
• Air pollution in cities and populated areas
• Large scale international or global
• Poorly understood and extremely complex
• Global problems such as acid rain, global
  warming, ozone layer depletion

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Particulate Pollutants

• Particulates - small particles and aerosols
  (1-100 µm)
• Responsible for color and opacity in smoke and
  haze
• Classification based on their properties
• Dust solid particles of large size
• Fume solid particles formed by condensation of
  vapors
• Mist liquid particles formed by the
  condensation of vapors/chemical reactions
• Smoke Solid particles formed as a result of
  incomplete combustion of carbonaceous materials
• Spray liquid particles formed by atomization of
  a parent liquid

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Effects of Air Pollutants
Abrasion not so common soil particles in dust
storms/Pb particles from
automatic
weapons fired Deposition removal liquid and
solid particle on exposed surface
Aesthetic issue
cleaning process causes damage Direct
chemical attack Solubilization
Oxidation/reduction reactions SO2/SO3 H2O
CaCO3 ? CaSO4/CaSO42H2O (leach away with
rainwater)
(limestone) Ag H2S ?AgS (slightly greyish
black) Tarnishing
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Effects of Air Pollutants
Indirect chemical attack Pollutants are absorbed
then react with component
of absorbent to form
destructive compound SO2 absorbed on leather
form H2SO4 due to the presence of Iron Leather
becomes brittle Electrochemical corrosion
Primarily oxidation/reduction reactions on metal

surfaces- forming microscopic anode and
cathode
Factor affecting deterioration Moisture,
temperature, sunlight and position of exposed
material etc.
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Effects of Air Pollutants
Leaf Primary indicator of air pollution on
plants In most cases, plants are more
sensitive than human Ozone Formation of
red-brown spot on leaves turning to white after
few days (Injury maximum
during sunny midday) NO2 Growth inhibition
at 0.5 ppm or higher necrosis (surface
spotting) SO2 Necrosis at 0.3 ppm Air
pollution reduction in surface area-resulting a
lower crop yield
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Effects of Air Pollutants

• Air quality standards to protect the most
  sensitive population
• we breathe about 20,000
  times/day
• Respiratory system primary indicator of air
  pollution effects on human
• Upper Respiratory Tract (URT) nose, pharynx
  (far-inks), larynx
• (lar-inks) , trachea (tray-kee-uh)
• Tiny hairs called cilia protect the nasal
  passageways and other parts of
• the respiratory tract, filtering out dust and
  other particles
• Lower Respiratory Tract (LRT) branching
  structures-bronchi and lung
• Bronchi end in tiny air sacs called alveoli
  (al-vee-oh-lie), where the
• exchange of oxygen and carbon dioxide actually
  takes place

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Inhalation and Retention of Air
pollutants (govern by size and breathing
rate) Size 5 to 10 ?m (visible by naked
eye) Effectively retained by hairs
in nose Sneezing also helps
screening Size 1-2 ?m Small enough to be
bypass screening/deposition in the
URT and penetrate to alveoli high
terminal settling velocity
deposit and do the most damage Size 0.5 ?m
Too small to be deposited diffuse to alveolar
wall

• Effect of Pollutant Concentration X Exposure
  time

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Chronic Respiratory Disease
Asthma Inflammatory lung disease that causes
airways to tighten and narrow (20
million suffer in the US) Bronchiolitis
Respiratory infection that affects the tiny
airways Pulmonary emphysema Lungs produce
excessive mucus and the alveoli
become damaged primarily
due to smoking Lung cancer Caused by an
abnormal growth of cells in the lungs
Q How debris is moved out of the lungs?
A. the cough reflex B. smoking
C. cilia D. Both A and C.
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Origin Fate of Air Pollutants

• Carbon monoxide
• A product of incomplete combustion of carbon
  containing compounds.
• e.g. fossil fuels (gasoline, diesel, coal),
  biomass, forest fire, etc.
• Major Sinks 1. react with OH. to form carbon
  dioxide
• 2. remove by soil microbes
• Hazardous Air Pollutant (HAPs) (page 24/25)
• Major sources include fuel combustion, metal
  processing, petroleum and natural gas production,
  waste/wastewater treatment, and many other
  industrial processes.
• Major Sinks Add./subs. of OH to form carbon
  monoxide/carbon dioxide
• Lead
• Volcanic activity, airborne soil (natural)
  Smelters, refining and incineration of
  lead-bearing wastes (anthropogenic).
• Major Sinks Attach to particles/form nuclei
  settle/wash-out by rain

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Origin Fate of Air Pollutants

• Nitrogen Dioxide
• Biological release of nitrous oxide (N2O) reaches
  upper atmosphere reacts with atomic oxygen and
  produce NO, which is then oxidized to NO2 by
  ozone.
• Burning of fossil fuels (coal and petroleum) is
  the major source of NO2.
• Major Sinks NO2 is converted to NO2-/NO3- and
  precipitates as acid rain
• Sulfur Oxides
• Contribute by coal based power plants,
  volcano, automobiles etc. contributed by
  atmospheric reactions-secondary pollutants.
• Major Sinks SO2 is converted to SO3-/SO4-
  and precipitates as acid rain

• Particulates
• Contribute by coal based power plants,
  volcano, automobiles, smokes
• from forest fires, soil dust etc.
• Major Sinks direct deposition, rain
  wash-out etc.

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• Photochemical Oxidants
• Entirely contributed by atmospheric
  reactions-secondary pollutants.
• Pollutants such as ozone and peroxylacetyl
  nitrate (PAN), which are
• formed in the atmosphere by a
  photochemical reaction or by hydrolysis or
  oxidation

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Global Issues of Air Pollution

• The effect of air pollution on regional and
  global levels
• Acid rain
• Ozone layer depletion
• Green house effect and Global warming

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Acid Rain
Page 485
Distilled water, which contains no carbon
dioxide, has a neutral pH of 7. "Clean" or
unpolluted rain has an acidic pH of 5.6, because
carbon dioxide and water in the air react
together to form carbonic acid, a weak acid. If
the rain water pH is below 5.6, then it is termed
as Acid Rain or more correctly Acid
Precipitation.
H2O CO2 ? H2CO3

• Causes of Acid Rain
• Sulfur dioxide (SO2) and Nitrogen oxides (NOx)
  released into the
• atmosphere during combustion of fossil fuels
  (coals, gasoline, petrol etc.).
• SO2 and NOx are converted to sulfuric acid
  (H2SO4) and nitric acid
• (HNO3) and through oxidation and
  dissolution.
• 2SO2 H2O O2 ? 2H2SO4
• 4NO2 2H2O O2 ? 4HNO3
• These acids then falls to ground with rain,
  snow or sleet Acids Rain

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Effects of Acid Rain

• Trans-boundary SO2 release in US has been blamed
  for forest
• destruction in
  Canada
• 
  in Britain - Scandinavia
• Destructs forest and crops due to increase in
  soil acidity
• Kills fish due to aluminum toxicity
• Damages building, erodes metal works, etc.

Forest destruction
Fish kill
Castle stonework in the UK
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Control/Preventive Measures

• Use fossil fuels with low sulfur content
• Install FGD in coal-fired power plant
• Seek for non-polluting energy sources, e.g.
  hydro, tidal power, wind, biomass, etc.

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Ozone Layer in Atmosphere
Presence of ozone in the upper atmosphere (20-40
km and up) provides a barrier to UV
radiation Thickness of Ozone 200-300 Dobson Unit
(DU) 1 Dobson Unit (DU) is defined to be 0.01 mm
thickness at STP.
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Importance of Ozone in Atmosphere

• Block harmful UV radiation reaching the earth,
  which otherwise will have the following
  consequences
• Incidence of skin cancer upon exposure
• Cataracts
• Cause aging
• Immune-system damage
• Reduction in crop yield

Cataracts
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How is Ozone Layer Depleted?
Page 486
Chlorofluorocarbons (CFC) pressuring agent,
refrigerants foaming agent, solvent etc.
CCl3F h? ? CCl2 Cl
Cl O3 ? ClO O2
ClO O ? Cl O2
One atom of Cl can destroy upto 100,000 molecule
of O3
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Control/Preventive Measures

• Montreal Protocol 1987 To phase-out CFC use
• Replace CFC
• HCFC Hydro Chlorofluorocarbon
• HFC Hydro fluorocarbon

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Green House Effect and Global Warming
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Green House Gases

• Any gas that absorbs infra-red radiation in the
  atmosphere is greenhouse gas
• Water vapor
• Carbon dioxide (CO2) major concern !!!
• Methane (CH4)
• Nitrous oxide (N2O)
• CFCs
• Ozone (O3)
• Hydrofluorocarbons (HFCs)

Page 489
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Green house gases
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Global Warming and Effects

• Global warming Average increase in the Earth's
  temperature.
• Changes in earth climate
• Changes in rainfall patterns
• A rise in sea level
• Impacts on plants, wildlife, and humans

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Air Pollution Control Devices

• Absorption Tower
• Baghouse
• Venturi Scrubber
• Cyclone Separator
• Adsorption Bed
• Electrostatic Precipitator

Page 511
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Particulate Pollutants

• Classification based on their sizes
• Total suspended particulates (TSP)
• Respirable suspended particulates (RSP)
• Particulate matter which is very small, remains
  suspended in the air for periods of time, and is
  easily inhaled into the deep lung
• PM10 Particulate matter 10 µm
• PM2.5 Particulate matter 2.5 µm
• Particulate pollutants that are of particular
  concern are RSP, lead, asbestos, heavy metal
  compounds, and radioactive substances.

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Gaseous Pollutants
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Important Gaseous Pollutants

• Sulfur dioxide
• Major source is the combustion of fossil fuel.
  Coal fired power stations contribute most to SO2
  pollution.
• Nitrogen oxides
• High temperature processes (combustion) produce
  NO, which is then oxidized to NO2 in the ambient
  air.
• Burning of fossil fuels (coal and petroleum) is
  the major source of NOx.
• Carbon monoxide
• A product of incomplete combustion of carbon
  containing compounds.
• It is a localized pollutant and tends to build up
  in areas of concentrated vehicle traffic, in
  parking garages, and under building overhangs.

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Important Gaseous Pollutants

• Carbon dioxide
• One of the trace elements in the atmosphere
• Increase in its concentration play a crucial
  role in altering the climate of the earth
  (greenhouse effect)
• Hydrocarbons
• Vehicles are major source of atmospheric
  hydrocarbons.
• Stationary sources include petrochemical
  manufacturing, oil refining, oil refining,
  incineration, paint manufacturing and use, and
  dry cleaning.
• Ozone
• A secondary pollutant, which is not emitted
  directly into the air, but is the result of
  chemical reactions in the ambient air.
• The components of automobile exhaust are
  particularly important in the formation of ozone.

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Thermal Power Plant Control/Preventive Measures

• Use fossil fuels with low sulfur content
• Install FGD in coal-fired power plant
• SO2 CaCO3 ? CaSO3
• (Limestone) CO2
• CaSO3 ½ O2 ? CaSO4
• (Gypsum)

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Thermal Power Plant Control/Preventive Measures
(cont.)

• Reduction of NOx by ammonia
• 6NO 4NH3 ? 5N2 H2O
• 6NO2 8 NH3 ?7N2 12 H2O
• Seek for non-polluting energy sources, e.g.
  hydro, tidal power, wind, biomass, etc.

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Absorption Tower

• Transfer of pollutants from gas phase to
  liquid phase
• Mass transfer process ? gas dissolves in
  liquid

Three steps for pollutant gas removal
Dissolution of gas pollutant into liquid
Gas/liquid interface
Diffusion of gas pollutant to surface of liquid
Page 511
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Absorption Tower (cont.)
Liquid solvents Water, Acid/Base solution
Gas pollutants Sulfur dioxide, Hydrogen
sulfide, Chlorine, Nitrogen oxides,

• Spray chamber Liquid is sprayed to capture
  the
• air pollutants as the gas move upward in
  chamber
• Plate Tower Liquid passes thru a number of
  plates
• and forms thin film that captures the
  uprising gas
• pollutants
• Packed Tower Liquid passed thru packed column
  
• tower and captures the gas pollutants as they
  move
• upward thru the liquid film.

Page 511
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Absorption Systems
Lower water use (1 to 3 L/m3 gas ) High surface
area for absorption Efficiency 90
Higher water use (3 to 14L/m3 gas ) Much lower
surface area for absorption Efficiency 50-75
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Baghouse

• Consists of banks of
• fabric filters, usually
• bags
• ?0.1-0.35 mL2-10 m
• Contaminant air flows
• into the bottom of
• baghouse and pass
• thru the fabric filter
• Particulate is trapped at the fabric filter and
  accumulate
• Mainly for the removal of particulate matters,
• Efficiency 99.

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Venturi Scrubber

• Baghouse not suitable
• for wet, corrosive and
• hot particulate matter
• Absorption systems not
• suitable for fine particles
• Venturi scrubber is an
• ideal solution
• The differential velocity between the liquid
  droplets
• and particulate matters.
• This differential velocity allows the particles
  to get
• collected on the droplets

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Cyclone Separator

• For the removal of
• particulate matter ? 10 ?m
• Particle-laden gas enters
• the cyclone tangentially
• Separation of particles
• occurs as a result of
• centrifugal force
• The heavy particles are thrown on the wall and
  slough
• off into a collection hopper.

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Adsorption Bed

• The target pollutants (absorbate) from gas are
• removed thru attachment on the surface of the
  media
• The media (absorbent) is typically granulated
• activated carbon (GAC) or powdered activated
• carbon (PAC)
• Activated carbon is produced from nut shell
• (coconut) and coal subjected to heat treatment
  in a
• reducing atmosphere.
• Effective in removal organic gaseous pollutants,
  e.g.
• hydrocarbons Efficiency 99

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Electrostatic Precipitator

• Dry removal of particles from gas streams
• Alternating plates and wires with large direct
  current
• potential (30 -75 kV) is established between
  the
• plates
• This creates an ion field between the plates
• As particle-laden gas stream passes the field,
  ions
• attach to the particle, giving them net ve
  charge
• The particles then migrate toward the ve
  charged
• plate where they stick

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Electrostatic Precipitator
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Air Pollution Control in Mobile Source
Catalytic converter treats the exhaust before it
leaves the car and removes a lot of the pollution
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Air Pollution control in Mobile Source
The Reduction CatalystThe reduction catalyst
uses platinum and rhodium to help reduce the NOx
emissions. 2NO N2 O2 or 2NO2 N2 2O2
The Oxidization CatalystThe oxidation catalyst
reduces the unburned hydrocarbons and carbon
monoxide by oxidizing them over a platinum and
palladium catalyst. This catalyst aids the
reaction of the CO and hydrocarbons with the
remaining oxygen in the exhaust gas. For example
2CO O2 2CO2
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Meteorology

• Lapse rate Change of air temperature with height
• Ambient lapse rate (-?T/?Z) Rate of ambient
  temp. changes
• Ambient lapse rate different than the lapse rate
  of rising air parcel (from stack, automobile,
  etc.)
• Adiabatic lapse rate (? -dT/dz) Change in
  temp. of air parcel with no heat loss/gain with
  ambient air

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Stability

• Tendency of atmosphere to resist/enhance the
  vertical motion of air parcel
• Three types of stability
• Neutral When both lapse rates are exactly equal
• (? ?T/?Z)
• Unstable Rising air parcel warmer than the
  ambient air and the parcel will continue to rise
• (?T/?Z ?)
• Stable Rising air parcel arrives at altitude in
  a cooler state than the ambient air. Displaced
  parcel of air downward
• ?T/?Z

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• Neutral Stability ? ?T/?Z -1.00oC/100 m

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• Unstable atmosphere ambient temp. falls at a
  faster rate that the dry adiabatic rate, i.e.
  ?T/?Z ?
• ?T/?Z -1.25 oC/100 m

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• Stable atmosphere ambient temp. falls at a
  rate less than the dry adiabatic rate, i.e.
  ?T/?Z
• ?T/?Z -0.5 oC/100 m

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Transport of Air Pollutants
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Meteorology of Air Pollution
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Inversion
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This is the end !