Atmosphere & Atmospheric Pollution
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Transcript of Atmosphere & Atmospheric Pollution
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The Atmosphere
Troposphere, Stratosphere,
Mesosphere, Thermosphere,
Exosphere
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ATMOSPHERE
Atmosphere extends about 2000 km above
Earths surface
Atmosphere divided into four regionsy Troposphere
y Stratosphere (Ozone Layer)
y Mesosphere
y
Thermosphere
Atmosphere is less dense the high you go
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ATMOSPHERE
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ATMOSPHERE
Temperature inversion is seen between the
different regions
Dry atmosphere
y 78.1% N2
y 20.9%O2
y
0.9% Ary 0.03% CO2
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TROPOSPHERE
Important reactions in the troposphere are
photosynthesis & nitrogen fixation
The concentration of carbon dioxide in theatmosphere depends on photosynthesis,
repsiration & the amount of CO2 dissolved in
surface waters (including oceans)
Carbon cycle & nitrogen cycle (know these!)
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Atmospheric Pollution
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ATMOSPHERIC POLLUTION - INTRO
Emissions of pollutants into the atmosphere arein two forms
y Gases
y Particulate material
Particulate material
y Dust & liquid droplets
y Size = 108m 104m
y Can also absorb gases
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POLLUTANTS TYPES
Pollutants are either primary pollutants or
secondary pollutants
Primary pollutantsy Emitted directly into the atmosphere
Secondary pollutants
y
Formed indirectly by reactions in the atmosphere
*Residence time is the length of time a particular chemical is present
in a given reservoir
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ATMOSPHERIC EMISSIONSFATE
Emissions either
y Accumulate in the atmosphere or
y Those that are unreactive in troposphere escape to
the stratosphere & participate in chemical reactions
Main air pollutants
y Oxides of carbon (CO, CO2)
y Sulphur dioxide (SO2)
y Hydrogen sulphide (H2S)
y Oxides of nitrogen (NO, NO2)
y Ozone (O3)
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SOURCES OF MAIN ATMOSPHERIC
POLLUTANTS
Pollutant Pollutions
Sources
Natural
Sources
Residence
Time*
Carbon dioxide Combustion Biological
decay
4 yrs
Carbon Monoxide Transport
Combustion
Forest fires 1-4 months
Hydrocarbons Transport
Combustion
Biological
processes
16 yrs
Halogenocarbons
(CFCs)
Aerosols
Refrigerants
- over 20 yrs
Sulphur Dioxide Combustionof fossil fuels
Volcanoes 3 7 days
Nitrogen Oxides Combustion Biological
processes
4 days
Particulates Combustion Dust Varies
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Oxides of Carbon
Carbon Dioxide & Carbon Monoxide
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CARBON MONOXIDE & CARBON DIOXIDE
Carbon Monoxide (CO) & Carbon Dioxide (CO2)
are the largest produced air pollutants
Main sourcesy Decomposition of organic material
y Oxidation of methane
y Combustion of fossil fuels
566kJH;2 OO2 O
220kJH;2 OO2
2(g)2(g)(g)
(g)2(g)(s)
!(p
!(p
S
S
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CARBON MONOXIDE SOURCES
Naturally
y Oxidation of methane in swamps
y Oxidation of organic material in tropics
y
These sources account for most of CO in theatmosphere (more than human activities)
Human activities
y Combustion of fossil fuels
y 56% is for petrol used in transport
y CO produced during idling or deceleration of vehicles
y Other 44% heating, cooking, electricity etc
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CARBON MONOXIDE SINKS
Carbon monoxide can be removed by
1. Reactions in troposphere
y This removes up to 50% of carbon monoxide emitted
in the troposphere
HOOOH 2 yy p
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CARBON MONOXIDE SINKS
Carbon monoxide can be removed by
2. Soil Bacteria (e.g.Bacillus oligocarbophilus,Methanosarcina backerii ) or Soil Fungi
y Uptake of CO by soil bacteria is rapid
backeriiby
by
O3HOHO4
O2OO2
2(g)(g)4(l)2(g)
2(g)2(g)(g)
cinaMethanosar
ophilusoligiocarbBacillus
p
p
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CARBON MONOXIDE SINKS
Carbon monoxide can also be removed
3.
y Or by plant leaves
MCO2MOCO 2(g)(g)(g) p
COleavesplantCO
CH(R)COOHNHleavesplantCO
2(g)(g)
acidsamino2(g)
night
hf
p
p
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EFFECTS OF CARBON MONOXIDE
Carboxyhaemoglobin
y Carbon monoxide combines with haemoglobin
y CO not easily released
y
Haemoglobin not able to transport oxygen aroundbody
Effects/Symptoms of CO poisoning
y Reddening of lips (cherry lips)
y Unconsciousness
y Death by asphyxiation
y Parkinsons disease (rare cases)
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CARBON DIOXIDE SOURCES
Biological decay
Burning of petrol (fossil fuels)
y Accounts for 31% of CO2 emissions
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CARBON DIOXIDE CONCENTRATION
Levels of CO2 in the atmosphere have shown
steady increase since 1870
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CARBON DIOXIDE SEASONALVARIATION
There are seasonal variations in CO2concentration
y Northern Hemisphere Peaks in April & at lowest in
SepOct
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CARBON DIOXIDE VARIATION
Seasonal variations are mainly due to
photosynthesis
y
Destruction of rainforest can significantly raise thelevels of carbon dioxide in the atmosphere
Temperature change of 23 oC would have
pronounced effect on global & local climate
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GREENHOUSE EFFECT
Average temperature of the Earth is maintained
at 14 oC
y Achieved by re-emitted IR radiation trapped by water
vapour & CO2 (greenhouse gases)
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GREENHOUSE EFFECT
If it was not for the re-emitted IR radiation from
water & CO2
y
EarthsG
lobal temperature at the surface would be 20 oC to 40 oC
This method by which the Earths surface is kept
relatively warm is called the greenhouse effect
y ~50% of energy from the sun reaches Earths surface
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GLOBAL WARMING
Concern
y Rising levels of CO2 in the atmosphere & othergreenhouse gases will lead to GLOBAL WARMING
y Disastrous climatic effects
Greenhouse gases
y Water vapour
y Carbon dioxide (CO2
)
y Methane
y Nitrous Oxide
y Ozone
y CFCs
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Sulphur Dioxide
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SULPHUR DIOXIDE SO2
Primary pollutant
Residence Time = 3 7 days
150 million tonnes/yr of SO2 discharged in
atmosphere
y Burning of fossil fuels, HFO (generate electricity)
y Coal
y Smelting (Extration of Zn, Pb, Cu)
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SULPHUR TRIOXIDE SO3
Secondary pollutant
Sulphur dioxide (SO2) is oxidized to sulphur
trioxide (SO3) which then reacts with water toform sulphuric acid (H2SO4)
4232 SOSOSO pp
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SULPHUR TRIOXIDE SO3
Sulphur dioxide in the atmosphere can be
oxidized to sulphur trioxide in three ways:
y Free-Radical Oxidation
y Catalysis
y Photochemical Oxidation
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OXIDATION OF SULPHUR DIOXIDE
CATALYSIS
Overall reaction is oxidised in water droplets &catalysed by metal ions & metal oxides
y Mn2+, Fe3+, Cu2+
y
Oxides of Cr, Al, Pb, Ca
Surfaces of buildings act as catalytic centres
4(aq)22(g)(l)22(g) O2HOO2HO2 p
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OXIDATION OF SULPHUR DIOXIDE
PHOTOCHEMICAL OXIDATION
Reaction occurs rapid in water droplets Ozone
is destroyed
Nitrogen dioxide from motor vehicle emissions
can increase the rate of oxidation
2(g)3(g)3(g)2(g) OSOOSO p
(g)3(g)2(g)2(g) NOSONOSO p
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ACID RAIN
Acid rain is produced when SO2 is dissolved in
water to give sulphurous & sulphuric acid (H2SO3& H2SO4)
Pure Rainwater has a pH ~ 5.6
Rain water + SO2 emissions pH ~ 2
SO2 is the main cause of acid rain, Nitrogen oxideemissions also contribute when dissolved in
water droplets (nitric acid)
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ACID RAIN
Nitrogen oxide emissions originate from power
stations & motor vehicles
Acid rainy Increase acidity of lakes
y Destroy aquatic life
y Leaches nutrients from soils
y Enables toxic metal ions to enter soil solution, food
chain, drinking watersupplies
y Corrosion of metals & buildings containing limestone
y Affect the growth of trees
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ACID RAIN CORROSION OF BUILDINGS &
METALS
Sulphur dioxide & sulphuric acid has a corrosive
effect
y Buildings, metals, paper & clothing fabrics
CaCO3 in limestone is converted to the more
water soluble CaSO4 by sulphur dioxide &
sulphuric acid
2(g)4(s)2(g)2(g)3(s) O2a O2O2 O2 a O p
2(g)(l)24(s)4(aq)23(s) OOHa OOHa O p
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ACID RAIN CORROSION OF METALS
Sulphur dioxide increase the rate of corrosion of
metals
Sulphuric acid dissolves the metal protective
oxide layers (eg. Al or Cu) forming sulphates that
are water soluble
4(s)2(g)2(g)(s)FeSOOSOFe p
2(g)4(aq)4(aq)2(s) HFeSOSOHFe p
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EFFECT OF SULPHUR DIOXIDEHUMANS,
PLANTS &ANIMALS
Subject Effect
Humans Aggravate respiratory diseases
(eg. asthma, emphysema &
chronic bronchitis),
Irritation of eyes & respiratory
tract,
Affects heart ,
Reduce lung function,
Death
Plants Bleached spots on leaves,
Yellowing of leaves,Suppressed growth,
Inhibits photorespiration,
Chlorosis (loss of chlorophyll)
Animals Affects central nervous system
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CONTROLLING SULPHUR DIOXIDE
EMISSIONS
Reducing the sulphur content of fuels results in a
decrease in the amount of SO2 released when
fuels are burnt
Sulphur in crude oil is removed by CaO & then
oxidation in air
2(g)(s)2(g)(s)
2(g)(s)(s)(l)
O22 aO3O2 a
O2 a2 aO3
p
p
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CONTROLLING SULPHUR DIOXIDE
EMISSIONS
The SO2 produced is used to make sulphuric acid
by Contact Process
Gaseous SO2 emissions from power plants can beprevented by removing the sulphur dioxide by
scrubbing (using lime)
Limestone reacts with sulphur dioxide to formfine particles of calcium sulphate
4(s)2(g)2(g)(s)
2(g)(s)3(s)
a O2O2 O2 aO
OaOa O
p
p
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CONTROLLING SULPHUR DIOXIDE
EMISSIONS
The calcium sulphate produced can be used to
make sulphuric acid
Other bases such as magnesium oxide &ammonia can be used instead of CaO
y Endproduct can also be used to make sulphuric acid
Fewer nitrogen oxides are formed thus both SO2& NOx atmospheric pollutants are reduced using
scrubbing
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Photochemical Smog
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WHAT IS PHOTOCHEMICAL SMOG
Photochemical smog
y a whitish yellow haze which is a mixture ofsmoke &
fog
y contains chemical species which irritate the
respiratory tract
y causes long term effects on health
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PHOTOCHEMICAL SMOG CONSTITUENTS
Chemical pollutants in photochemical smog
y Nitrogen monoxide (NO)
y Nitrogen dioxide (NO2)
y Hydrocarbons
y Peroxyethanoyl nitrate (PAN)
y Ozone (O3)
y Aldehydes
Primary pollutants in photochemical smog are
nitrogen monoxide (NO) & hydrocarbons
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PHOTOCHEMICAL SMOG
Conditions needed to produced Photochemical
Smog
y A particular combination of atmospheric pollutants
y Sunlight
y Stable temperature inversion
y Land enclosed by hills
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PHOTOCHEMICAL SMOG
Primary pollutants (NO & hydrocarbons)concentrations increase during earlymorningrush hour traffic
y Nitrogen oxide (NO) is then oxidised to Nitrogendioxide (NO2)
Nitrogen dioxide concentrations fall later in theday due to
y Photolysis (complex series of reactions)
y Leads to formation of Ozone, Aldehydes &peroxynitrates
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COMPLEX REACTIONS
Formation of Ozone
Formation of Aldehydes
MOMOOONONO
2NOO2NO
322
22
p
p
p
yy
yy
hf
yy
yyyy
yy
yy
p
p
p
p
222
2222
radicalperoxyl2222
223
HORCHOOORCH
NOORCHNOORCH
ORCHORCH
OHRCHOHRCH
aldehyde
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COMPLEX REACTIONS
Formation of Peroxynitrates
Peroxyethanoyl nitrate (peroxyacetyl nitrate orPAN)
nitratenoylperoxyetha
22
OO
R OONONOR OO
p yy
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PHOTOCHEMICAL SMOG
Nitrous & nitric acids, (HNO2, HNO3) are formed
by reaction of nitrogen oxides (NOx) with water
Nitrogen oxides & hydrocarbons produced in theafternoon rush hour traffic are removed by
reaction with ozone
y Produces an aldehyde or ketone
methanal
aldehyde
yy
yy
yy
p!
p
COHor RCHOO
COOHRCHOOCHRCH
O2NOONO
2
232
223
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EFFECT OF PHOTOCHEMICAL SMOG
HUMANS & PLANTS
Subject Pollutant Effect
Humans NO2 Odour,
Lethal
Ozone Irritation of throat,
Shortness of breath,Irritation of eyes &
nose,
Impaired lung
function, chest pains,
coughing
Unconsciousness,
Death
PAN Reduced Lung
function
HCHO Odour,
Severe distress
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EFFECT OF PHOTOCHEMICAL SMOG
HUMANS & PLANTS
Subject Pollutant Effect
Plants NO2 Leaf lesions,
Inhibits
photosynthesis
Ozone Leaf lesions,Inhibits
photosynthesis
PAN Collapse of young
cells
HCHO Leaf symptoms
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Ozone
Stratospheric Ozone vs Tropospheric Ozone
Good vs Evil
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STRATOSPHERIC OZONE
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STRATOSPHERIC OZONE
Production of stratospheric ozone is by UV
radiation 190 242 nm
Ozone (O3) is a form of oxygen with three oxygenatoms
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STRATOSPHERIC OZONE PRODUCTION
Ozone is produced in stratosphere by
photochemical reactions
Overall Reaction???
OzoneofFormation(g)
ozone
3(g)(g)2(g)(g)
(g)(g)2(g)
MOMOOOOO
p
p
hf
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STRATOSPHERIC OZONE DESTRUCTION
Ozone (O3) produced absorbs UV radiation
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OZONE DESTRUCTION
Ozone can also be removed by other reactions
The oxides of nitrogen enter the atmosphere
y Biological activity
y Fossil Fuel combustion
(g)(g)(g)2
(g)2(g)(g)(g)2
(g)2(g)2(g)3(g)
ONONO
ONOONO
O2NOONO
p
p
p
yy
yy
yy
hf
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STRATOSPHERICVS TROPOSPHERIC
OZONE
Stratospheric Ozone is essential in screening the
Earth from dangerous UV radiation
y Ozone Layer absorbs most UV radiation < 320 nm
y Animals & plants are protected from this radiation
While Tropospheric Ozone????
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STRATOSPHERICVS TROPOSPHERIC
OZONE
Tropospheric Ozone is a dangerous pollutant
High tropospheric ozone concentrations results
from
y Motor vehicle emissions
y Incomplete combustions of fossil fuels
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TROPOSPHERIC OZONE
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TROPOSPHERIC OZONEREACTIONS
All species are in the gaseous state
Nitrogen oxides participate in both the formation
& destruction of ozone
a OzoneofnDestructio
OzoneofFormation
223
32
2
22
O2NOONO
MOMOOONONO
2NOO2NO
p
p
p
p
yy
yy
yy
hf
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TROPOSPHERIC OZONE
Nitrogen monoxide (NO) produced from vehicle
exhausts in morning rush hour traffic leads to a
rise in Ozone (O3) levels
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EFFECT OF TROPOSPHERIC OZONE
HUMANS & PLANTS
Subject Effect
Humans Irritation of throat
Shortness of breath
Irritation of eyes & nose
Impaired lung function, chest
pains, coughingUnconsciousness
Death
Plants Leaf lesions, inhibits
photosynthesis
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OTHER EFFECTS OF TROPOSPHERIC
OZONE
Tropospheric Ozone can cause oxidative cleavage
in the C=C double bond in rubber (polymer)
y Rubber to crack
y Damage to car tyres
Tropospheric Ozone contributes to greenhouse
effect
y Absorbs IR radiation emitted at the Earths surface
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CFCs
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CFCS
Chlorofluorocarbons were used
y Aerosol cans
y Refrigerators
y Plastics
Properties of CFCs
y Lack of reactivity (very stable)
y Low flammability
y Low toxicity
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CFCS TROPOSPHERE VS STRATOSPHERE
Troposphere
y CFCs are unaffected by UV radiation
Stratosphere
y CFCs are susceptible to attack & release chlorine
atoms
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BALANCE OF OZONE STRATOSPHERE
Naturally for millions of years
y Chlorine atoms in the stratosphere react with CH4 to
form hydrogen chloride or
y Chlorine atoms react with ozone to produce chlorine
monoxide (ClO) which then reacts with nitrogen
monoxide (NO) to form chlorine nitrate (ClNO3)
yy
p 34 CHHClCHCl
MClNOMNOClO
NOClNOClO
OClOOCl
32
2
23
p
p
p
yy
yyyy
yy
nitrate
chlorine
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BALANCE OF OZONE STRATOSPHERE
Naturally for millions of years, a balance of ozone in the
stratosphere has been maintained
HCl produced goes down into the troposphere where itdissolves in water & is washed out in rain
ClNO3 cannot react with ozone & is a temporary sink forchlorine atoms
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CFCS PROBLEMS
CFCs
y Large quantity of CFCs reaching the stratosphere
y Length of time they remain in the stratosphere
(unrecativity)
y CFCs produce additional Chlorine atoms (Cl.) in
stratosphere
y More Ozone (O3) is being destroyed than is being
created
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CFCS REACTIONS
CFCs Reactions that lead to a depletion of Ozone
Initiation
y Wavelength of radition required (175 220 nm)
yy
yy
p
p
ClCClCCl
ClCClCCl
23
222
hf
hf
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CFCS REACTIONS
Propogation
y Chlorine atoms (Cl.)is regenerated by reaction with
oxygen atoms & nitrogen monoxide
y Chlorine atoms (Cl.) produced react with more Ozone
leading to a loss of Ozone with absorption of radiation
yyyy
yy
yy
p
p
p
2
2
23
NOClNOClO
importantVeryOClOClO
OClOOCl
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CFCS REACTIONS
Termination
importanteryMClNOMNOClO
HHClHCl
CHHClCHCl
32
2
34
p
p
p
yy
yy
yy
nitratechlorine
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SUMMARY OF REACTIONS
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SUMMARY OF REACTIONS
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EFFECT OF CFCS - STRATOSPHERE
The above reactions leads to
y Thinning of the Ozone Layer
y Increased level of UV radiation reaching Earths
surface
Ozone depletion in stratosphere leads to
y Cooling of stratospherey Increase in temperature of troposphere
y Decrease in ozone levels in stratosphere
y Increase in ozone levels in troposphere
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OZONE HOLES AT THE POLES
Most Ozone is produced in the tropics &
transported to the poles
y Chlorine gas is released from Chlorine nitrate
y Chlorine gas & chlorine nitrate can produce chlorine
atoms that react with ozone
y These reactions occur at the poles (Antartica)
2(g)33(g) ClHNOClNOHCl p
33
2
NOClClNOClClCl
yy
yy
p
p
hf
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CONTROLLING IMPACTS OF CFCS
1. Montreal Protocol (1987)
y 50 nations agree to restrict production &
consumption of CFCs
y Problem = (CFCs remain unreacted for 5080 yrs)
y Problem = Models predict it may take 100 yrs for
existing CFCs to disperse
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CONTROLLING IMPACTS OF CFCS
2. CFCs substitutes
y Hydrofluorocarbons (HFCs) &
Hydrochlorofluorocarbons (HCFCs)
y Problem = HFCs & HCFCs are greenhouse gases
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EFFECTS OF OZONE DEPLETION
Effects related to UV radiation
y More UV radiation (
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EFFECTS OF OZONE DEPLETION
Importance of Plankton (zooplankton &
phytoplankton)
y Beginning of the food chain for all animals living in
the sea
Phytoplankton
y Give out oxygen into the water & atmosphere
y Only need H2O, CO2, salts & sunlight
Zooplankton
y Feed on phytoplankton
y Eaten by fish which are eaten by animals & humans
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Summary of Atmospheric
Pollution
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SUMMARY
Pollution of the atmosphere is caused mainly by
industrial & motor-vehicle emissions
Primary pollutants are the original gases or
particulates emitted
Secondary pollutants are formed by reactions
involving primary pollutants
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SUMMARY
Main primary pollutants are carbon dioxide,
carbon monoxide, sulphur dioxide & nitrogen
oxides
Secondary pollutants, formed mainly by
photochemical processes, are ozone,
peroxyethanoyl nitrate (PAN) & methanal
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SUMMARY
Use of catalytic converters in the car engines
vehichle exhaust system will enable maximum
fuel economy & oxidation of CO & hydrocarbon
emissions
CFCs were used in fridges & aerosols because of
their inactivity. This same inactivity enables
them to reach the stratosphere, where they causedestruction of ozone