atmosphere & atmospheric pollution

8/8/2019 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 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 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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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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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


50/82

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


59/82

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


62/82

CFCs


63/82

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


75/82

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


76/82

CONTROLLING IMPACTS OF CFCS

2. CFCs substitutes

y Hydrofluorocarbons (HFCs) &

Hydrochlorofluorocarbons (HCFCs)

y Problem = HFCs & HCFCs are greenhouse gases


77/82

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

atmosphere & atmospheric pollution

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