greenchemistryteacher spack

8/12/2019 GreenChemistryTeacher SPack

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A TeacherA Teacher s Pack providings Pack providing

background knowledge forbackground knowledge forteachers, lesson plans andteachers, lesson plans andresources for use in classresources for use in class

L isette V ote


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L. H. Vote GCE Green Chemistry Teachers Pack

Introduction

The purpose of this Teachers Pack is to provide teachers with a full resource on Green

Chemistry, covering all the specifications requirements for A-Level chemistry. Green

Chemistry is a new and/or enlarged topic in all the new specifications for teaching in

September 2008, following the new QCA GCE Chemistry Criteria. I reasoned that

many teachers themselves may not have had the opportunity to study environmental

chemistry as it is a relatively modern and current topic; and even if it was studied at

university, there may be some gaps in their knowledge, such as recycling and how it is

done; or they may not be up to date on the chemistry and issues as they stand today.

This resource would therefore allow them to fully understand the subject so they can

be very comfortable teaching it by knowing the background material, beyond what it

expressly required from the specifications. This would allow them, for example, to be

able to explain or answer pupils Green Chemistry-based questions on issues beyond

the syllabus. Furthermore, this pack would provide teachers with lesson plans and

resources, which would be useful when teaching a new and relatively unfamiliar

topic.

This resource therefore comes in two main sections: Firstly, a text-book allowingteachers to become up-to-date on Green Chemistry today. This is based on the

required knowledge in all the A-Level Chemistry specifications (i.e. AQA, Edexcel

and OCR A and B), for both AS and A2, however in much more detail than the pupils

are required to know, in order to provide teachers with the confidence and background

knowledge required to teach these new topics well. The second main section is a

collection of lesson plans and resources on Green Chemistry-based topics. These

lesson plans can be used as just that, a plan for an entire lesson; or ideas and activities

can be used from them and attached to your other lessons where the chemistry might

link together with Green Chemistry. The plans also suggest resources to use, such as

animations, video clips, worksheets, links and PowerPoint presentations; all of which

I have attached to this resource.

The topics I have covered are, Atmospheric Chemistry, including the Ozone Hole; Air

Pollution, including smog, catalytic converters and acid rain; Global Warming,

including the notions of carbon neutral, carbon footprint, biofuels and examples of

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them; and Recycling, including recycling, amongst other methods of disposal of

aluminium, iron, steel and polymers and issues associated with their disposal.

I hope you find this pack useful and practical; and that your pupils enjoyment and

understanding of Green Chemistry is increased.

February 2008

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What is Green Chemistry?

Green Chemistry is based on and ties together a variety of strings of chemistry:

Organic, Inorganic, Physical, Environmental, Biochemistry and Analytical Chemistry.

Green Chemistry and Environmental Chemistry, while often confused are two

separate fields. Green Chemistry encourages environmentally conscious behaviour,

such as reducing and preventing pollution and the destruction of the planet. On the

other hand, Environmental Chemistry is simply the study of chemistry occurring in

the environment. i

The following page lists the Twelve Principles of Green Chemistry, reproduced from

the Royal Society of Chemistry.

i Green Chemistry , Wikipedia, site accessed March 2008http://en.wikipedia.org/wiki/Green_chemistry

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The twelve principles of green chemistry It is better to prevent waste than to treat or clean up waste after it is formed.

Synthetic methods should be designed to maximize the incorporation of allmaterials used in the process into the final product.

Wherever practicable, synthetic methodologies should be designed to useand generate substances that possess little or no toxicity to human health andthe environment.

Chemical products should be designed to preserve efficacy of function whilereducing toxicity.

The use of auxiliary substances (solvents, separation agents, etc .) should bemade unnecessary whenever possible and innocuous when used.

Energy requirements should be recognized for their environmental andeconomic impacts and should be minimized. Synthetic methods should beconducted at ambient temperature and pressure.

A raw material or feedstock should be renewable rather than depletingwhenever technically and economically practicable.

Unnecessary derivatization (blocking group, protection / deprotection,temporary modification of physical / chemical processes) should be avoidedwhenever possible.

Catalytic reagents (as selective as possible) are superior to stoichiometricreagents.

Chemical products should be designed so that at the end of their functionthey do not persist in the environment, and break down into innocuousdegradation products.

Analytical methodologies need to be further developed to allow for real-time,in-process monitoring and control prior to the formation of hazardous

substances. Substances and the form of a substance used in a chemical process should

be chosen so as to minimize the potential for chemical accidents, includingreleases, explosions, and fires.

These principles have been reprinted with permission from Paul T. Anstas and JohnC. Warner Green Chemistry: Theory and Practice , New York: Oxford UniversityPress, 1998


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Table of Contents

1. Atmospheric Chemistry 1

1.1 Planetary Atmospheres 1

1.2 The Earths Atmosphere 2

1.3 Explanation for the Temperature Structure of the Atmosphere 3

1.4 Natural Catalytic Cycles: Problem with the Chapman mechanism 6

1.5 The Ozone Hole 8

1.5.1 Ozone Depletion 8

1.5.2 Why the Depletion is Dangerous 10

1.5.3 Explanation for the depletion 11

1.5.3.1 Polar Stratospheric Clouds 11

1.5.3.2 CFCs converting to Active Forms of Chlorine and Bromine 13

1.5.3.3 The Return of Sunlight: Ozone Destruction 13

1.5.3.4 Summary of Ozone Destruction 14

1.5.4 Current and Future Ozone Levels 15

1.5.5 CFC Substitutes 15

2. Air Pollution 19

2.1 Emitted Pollutants 20

2.2 Removal Processes of Compounds 21

2.3 Smog Formation 22

2.4 UK Emissions Today 25

2.5 Catalytic Converters 26

2.6 Acid Rain 27

3. Global Warming 30

3.1 Greenhouse Effect 30

3.2 Climate Change 30

3.3 Global Warming 31

3.3.1 Greenhouse Gases and How They Work 31

3.3.2 Evidence for Global Warming 31

3.3.3 Global Warming Potential 35

3.3.4 Carbon Neutral, Biofuels and Carbon Footprint 35

3.3.5 Controlling Global Warming and the Kyoto Protocol 37

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4. Recycling 40

4.1 Why Recycle 40

4.1.1 Household Waste 42

4.1.2 Aluminium and Steel 434.1.3 Plastics and Polymers 48

5. Lesson Plans and Resources 55

Lesson Plan: AS Module 1 Combustion of Alkanes: Air Pollution 56

Lesson Plan: AS Module 2 Extraction of Metals, Acid Rain and Recycling 58

Lesson Plan: AS Module 2 Ozone Destruction 59

Lesson Plan: AS Module 2 Global Warming 60

Lesson Plan: A2 Module 4 Disposal and Recycling of Polymers 61Additional Green Chemistry Resources 62

References 63


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1. Atmospheric Chemistry


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1. Atmospheric Chemistry

1.1. Planetary Atmospheres

The Earths atmosphere is the only planet within the solar system which contains such

a large percentage of oxygen; it is an oxidising atmosphere; as can be seen in the table

below.

Table 1: Major atmospheric constituents of the Sun and the Planets within the Solar System andtheir Surface Temperature 1

Planet/Star Most AbundantGas

2nd MostAbundant Gas

3rd Most AbundantGas

SurfaceTemperature (K)

Sun H 2 89% He 11% H 2O 0.1% --Venus CO 2 96.5% N 2 3.5% SO 2 0.015% 732Earth N 2 78.1% O 2 20.9% Ar 0.93% 288Mars CO 2 95.3% N 2 2.7% Ar 1.6% 223

Jupiter H 2 90% He 10% CH 4 0.24% 170Saturn H 2 96% He 4% CH 4 0.2% 130Uranus H 2 82% He 15% CH 4 2.3% 59.4

Neptune H 2 85% He 15% CH 4 1-2% 59.3Titan N 2 82% Ar 12% CH 4 3% 95

Table 2: Mass of the Sun and the planets within the Solar System 2 Planet

/StarSun Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune

Mass(kg)

1.99x10 30

3.30x10 23 4.87x1024

5.97x1024

6.42x10 23

1.90x10 27

5.68x10 26

8.68x10 25

1.02 x10 26

Mercury has a relatively low mass ( see Table 2 above) hence a smaller

gravitational force, and therefore has almost no atmosphere. Its thin

atmosphere is comprised of 98% He and 2% H 2.1

Venus has largely CO 2, which causes a runaway greenhouse effect and

hence its high surface temperature. 1

Mars atmosphere also consists chiefly of CO 2 but as it is of a lower mass than

Venus, its atmosphere is thinner as it has a weaker gravitational force. Thus,

there is not a very strong greenhouse effect. 1

The Outer Planets (Jupiter, Saturn, Uranus and Neptune) have a much lower

surface temperature due to their distance from the Sun. Their atmospheres are

predominately c. 90% H 2 and c. 10% He, and are reducing in nature as they do

not contain oxygen. There are low levels of a range of hydrocarbons in the

atmospheres, most likely to be caused by the photochemistry of CH 4.1

Titan is a satellite of Saturn and the only satellite to posses a massive

atmosphere; which here is of N 2 and some CH 4. Titans atmosphere contains

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photochemical smog: most likely to be due to the oxidation of hydrocarbons.

These aerosols cause the smog to appear as coloured clouds. 1

1.2. The Earths Atmosphere

The moon has c. 1/6 of the gravitational force than the Earth has, so it has virtually no

atmosphere. If the Earths atmosphere did not attenuate incoming solar radiation, the

temperature variation of the atmosphere would look like that of the moons 3 :

Figure 1: The temperature structure of the moons atmosphere and that of th e Earths, if theEarths atmosphere did not attenuate incoming solar radiation 3

The light from the sun heats up the Moons surface, which radiates heat upwards, sothe surface heats the atmospheric layers directly above it. Therefore, there is a high

temperature at the surface, which falls away rapidly as the distance from the surface

increases, as heat transfer is less effective. 1 However, the temperature structure of the

Earth has an S shape:

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Figure 2: Temperature variation with altitude of Earth's atmosphere 4

1.3. Explanation of the Temperature Structure of the Atmosphere

Troposphere decrease in temperature

From the surface to the Tropopause, the temperature decreases, this is due to the same

reason for the temperature structure of the moon (the Sun heats the Earths surface,

which re-radiates heat back up, heating the layers above it, with decreasing intensity

as the altitude increases).

Stratosphere increase in temperature

At 10-15 km the temperature begins to increase throughout the stratosphere. 1 This can

be explained by the absorption of solar radiation:

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the stratosphere. Ozones generation reaches a maximum in the Stratosphere because

it is a balance between number of photons and the concentration of O 2 molecules1:

At higher altitudes : There is a high number of photons (fewer have been absorbed

by the atmosphere), but the atmosphere is thinner, so the pressure low, therefore

there is a low concentration of O 2 molecules too low to create high enough

levels of O 3.

At lower altitudes : Despite the fact there is a higher pressure, hence higher

concentration of O 2, the number of photons is too low as the layers of atmosphere

above it have attenuated the incoming radiation this slows the rate of the first

step in the Chapman mechanism.

In the stratosphere, there is warm air sitting on top of cold air, so it is hard for the coldair to move through it: the air remains stuck in these distinct layers, which is termed

zonally symmetric 1.

Mesosphere decrease in temperature

Again, the air begins to cool here as the altitude increases, as the pressure decreases

and hence the concentration of M and O 2 molecules decrease, so there is very little to

kick-start 1 the Chapman cycle, and generation of ozone is extremely low.

Thermosphere increase in temperature

This begins at about 90 km, at this point the atmosphere is so thin and collisions

between particles are extremely infrequent. This means that most of the particles dont

get the chance to equilibrate once they have absorbed the high energy incoming solar

radiation, and therefore their translational temperatures become very high 1.

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1.4. Natural Catalytic Cycles: Problem with the Chapman mechanism

The Chapman mechanism predicted the right ozone generation mechanism but over-

predicted the production of O 3 by a factor of about 5. 1 This is because the last step in

the cycle:

is slow and there exist catalysts, X, which are species in parts of the atmosphere

which participate in the following cycle to speed up the destruction of ozone. This is

called natural catalytic cycles 1:

23 O2OO +

Species of X are: 3 223

2

23

OOOO:

OXOXO

OXOOX

++

++

++

Net

NO 30-40km e.g. NO

223

22

223

OOOO:

O NOO NO

O NOO

++

++

++

Net

Cl and Br maximum at 45km

HO above 45 km

H above 60 km

Sources of catalysts:

The catalysts are formed via the reactions outlined below. They involve a natural

source gas 1 reacting with another molecule or undergoing photolysis (i.e. the

compound is broken down by sunlight photons ).

Despite the fact that these species catalyse the destruction of ozone, these reactions

dont go on indefinitely, which would destroy the ozone layer. Fortunately,

termination reactions occur and this produces stable (inactive) reservoir

compounds 1 from the active radicals. These reservoir compounds are often the source

gases themselves 1.

Source of NO X:

Firstly, ozone undergoes photolysis to form oxygen and an excited oxygen

radical1

:

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)(OD)O(h O g1

21

3 ++

The source gas, N 2O is produced by soil, which goes on to react with the oxygen

radical to form NO 1:

MHNOMHO NO

2NOO ND)O(

32

21

+++

+

n Step:Terminatio

Source of Cl: 1

34

33

CHHClCHCl

ClCHh ClCH

++

++

n Step:Terminatio

Fortunately, the amount of CH 3Cl emitted into the atmosphere is very low.

However if this amount increases, it would present a problem as this is a very

efficient process ( see Table 3 ).

Source of HO X: 1

22222

222

341

21

OOHHOHO

OOHHOHO

CHOHCHD)O(

OHOHOHD)O(

++

++

++

++

n Step:Terminatio

Table 3: Rates of catalytic cycles

X K 220 / cm3 molecule -1 s-1 k b /k a

H 1.7 x10 -11 25000

HO 2.2 x10 -14 32

NO 3.5 x10 -15 5

Cl 8.7 x10 -12 12794

O 6.8 x10 -16 1

NB: k b /k a

b23

a223

OXOOX

OOOO

k

k ++

++

Rate loss of ozone:d[O 3]/dt=- k a[O][O 3]-k b[X][O 3]

The rates are equal when:k a[O][O 3]/k b[X][O 3]=1

a b k k /][ = O]/[X Natural Chapman cycle

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It can be seen from the above table that one only needs to add c.1 millionth of the

amount of H into the system compared to O for it to have the same effect as the

natural Chapman cycle.

1.5. The Ozone Hole

1.5.1. Ozone Depletion

In the 1970s, the British Antarctic Survey recorded an enormous decrease in ozone in

the Stratosphere over the Antarctic 6 . At first they believed their equipment to be

faulty as they were astonished by this finding 7 .This continued to decrease year on

year 8 , as shown by Figure 4.

Figure 4: Average Ozone Depletion f orOctober over the Antarctic 6

Figure 5: Average Area of the Ozone Hole1980-2006 8

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Figure 6: Graph to show the changes in Ozone Pa r tial Pressure over the South Pole from 1967-2001 3

As can be seen from Figure 6 , since about the mid-1970s there has been a remarkable

decrease in ozone partial pressures. There has also been an observed diminution over

mid-latitudes and in the Arctic 3. Every spring in the Antarctic (i.e. October), the

average ozone levels drop and ozone depletion reaches a maximum at the end of

November. The ozone hole develops seasonally over 6-8 weeks in the stratosphere,completely destroying ozone in some places. This seasonal change can be seen from

the figure overleaf:

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Figure 7: Graph showing the variation in Ozone Partial Pressure at various al titudes in thesummer (October) and winter (July) of 2001 over the Antarctic 9

As can be seen from the July bulge around 15km, this is where the ozone is usually at

its maximum in the stratosphere. In the winter, the ozone level is almost 0 at this

altitude, showing severe depletion.

1.5.2. Why the depletion is dangerous

Low levels or lack of ozone in the stratosphere causes detrimental impacts of humans,

the ecosystem, and the economy at large. This is primarily due to the fact that reduced

levels of ozone means that less of the dangerous, high energy UV-B radiation will be

absorbed ( see Figure 3 ), and so more will impinge upon the earths surface.

Approximately, a 1% decrease of ozone leads to a 2% increase of UV radiation

reaching the earths surface 3.

Humans: Increased levels of dangerous high-energy UVB radiation 17 impinging

upon the earths surface can cause melanoma and non-melanoma skin cancer 17,

eye disorders and cataracts and suppression of the immune system in people of all

races possibly leading to an increase in diseases and infections. According to

Tolba et al :

The percentage increases [of skin cancer] will not be one-to-one: a sustained

ten per cent reduction in ozone would result in a 26 per cent increase in non-

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melanoma skin cancer. All other things remaining constant, this would mean

an increase in excess of 300,000 cases a year, world-wide .17

Plants: Roughly half of the worlds plants are sensitive to UV-B light, and their

leaves shrink and the plant grows less when there is an increase in UV-B light

impinging on the earths surface. Economically, this is also problematic as it can

cause reduce food yields and plants also can change their chemical composition

with increased UV-B exposure, which can affect their quality and nutrient levels. 17

Aquatic ecosystems: Phytoplankton experience a similar detrimental impact of

excess UV-B radiation that terrestrial plants do. This could affect species further

up the food chain and have a detrimental impact on the productivity of fisheries 17,

amongst others. In addition, there could be nitrogen deficiency in rice paddies as:

Increased exposure to UV-B radiation could lead to decreased nitrogen

assimilation by prokaryotic micro-organisms 17

Air quality: Increased levels of surface UV radiation can change the levels of

reactive compounds in the troposphere, such as acids, hydrogen peroxide and

ozone where levels of NO x are high. 17

Materials damage: Photo-oxidation 3 can occur to many materials (wood, plastics

and rubber 17), which is when the materials become oxidized through the action of

UV light. Thus, increased UV light can cause increased damage to these materials.

1.5.3. Explanation for the depletion

1.5.3.1. Polar Stratospheric Clouds

In the Polar Regions in the winter, the temperatures drop so low that a polar vortex

forms. This is when sunlight does not shine upon the region, and it is so dark and coldthat air descends and creates a strong downwards vortex motion 1, or circumpolar

winds in the mid to low stratosphere 6. This isolates the air within the vortex from the

rest of the globe, and no material can get out and material can only enter at 40 km:

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Figure 8: Depiction of the Polar Vortex during the winter over the South Pole 10

In these conditions: no sunlight, and very cold temperatures below -80 0C polar

stratospheric clouds (PSC) can form, these clouds remain there as the vortex isolates

the air so it remains cold. These contain high levels of nitric acid (HNO 3) and ice-

water. 11

Figure 9: Depiction of how CFCs enter the atmosphere 6

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1.5.3.2. CFCs converting to Active Forms of Chlorine and Bromine

CFCs were first created in 1928 as a non-toxic, non-flammable refrigerant, and then

many other uses for them were discovered 7, due to their low reactivity and volatility.

As can be seen from the figure above, CFCs are emitted into the atmosphere by

factories and homes (such as through the use of CFCs in aerosols, refrigerants, in air-

conditioning and as solvents). The UV light in the upper atmosphere can easily break

the C-Cl bonds in CFCs and converts the compounds into the main reservoir species

of chlorine HCl and ClONO 2, as they have a long lifetime, and move down into the

polar vortex. The PSCs provide a surface on which heterogeneous reactions can occur

to convert these two species, and their bromine equivalents, into active forms of

chlorine11

:

3252

352

22

322

232

HNO2OHO N

ClONOHNOHClO N

ClOHHOClHCl

HOClHNOOHClONO

ClHNOClONOHCl

+

++

++

++

++

These heterogeneous reactions allow for the reservoir compounds of catalysts forozone destruction to rapidly convert chlorine and bromine to their active forms.

1.5.3.3. The Return of Sunlight: Ozone Destruction

Remembering this occurs in the winter, as the cold temperatures that occur allow the

formation of the PSCs; when the sunlight returns in the spring (October for the South

Pole), the molecular chlorine readily undergoes photolysis:

ClClCl 2 ++ h

This could now go on to catalyse the destruction of ozone through the cycle:

20km)(c.altitudeat thisslowtooisit-OClOClO

:cyclein thestepfinalthedovortex toin theatomsOenoughnotareereHowever th

OClOOCl

2

23

++

++

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Instead, the cold temperatures encourage the formation of dimers of ClO, which

drives the following cycle:

nDestructioOzone-2O2O: Net)O2(ClO)O2(Cl

OClClh ClOOCl

MClOOClMClOClO

23

23

2

++

+++

+++

This cycle is thought to be the predominant cycle for ozone destruction, accounting

for 70% of destruction in the South Pole.

1.5.3.4. Summary of Ozone Destruction

The greater the amount of CFCs released into the atmosphere, the greater the amount

of chlorine available as CFCs break with a high energy source:

i.e. light at 200 nm: CFCl 3 + h v CFCl 2. + Cl .

This free chlorine then goes on to catalytically destroy ozone. The following figure

depicts how ClO is rapidly created from CFCs in the polar vortex in the winter (i.e. in

the absence of sunlight), and how this destroys ozone in the presence of sunlight (i.e.

in the spring), and ClO levels continue to increase.

Figure 10: Graphs to show a comparison in the variations of ClO and Ozone i n the Antarcticvortex in the winter (28/08/87) and the spring (16/09/87) of 1987 12

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These same factors also cause destruction over the arctic, although because of warmer

temperatures, the loss isnt as great. In addition, the PSCs dont occur as strongly in

the northern hemisphere because the land-ocean distribution is different (the mountain

ranges stir the atmosphere up 11) and more favourable for their formation in the

southern hemisphere, and in the Arctic the polar vortex disperses earlier in thespring 11.

1.5.4. Current and Future Ozone Levels

Currently, the ozone hole is one and a half times the size of the United Sates ( see

Figure 11 ), and is still getting larger. However, levels of CFCs are decreasing. This is

due to legislations controlling the use of CFCs: the Vienna Convention 17 which did

not prevent the use of bromofluoroalkanes13

, and therefore the Montreal Protocol14

that were implemented in 1985 17 and 1989 14 respectively. These legislations were

supported by chemists. The Montreal Protocol aimed to reduce stratospheric halon

levels to the levels they were at before the ozone hole by 2060 11 .

The Montreal Protocol was written so that schedules for the phasing out of

halofluorocarbons could be revised depending on the current scientific and

technological advances 15 . Thus, most recently, in September 2007 a Montreal Summit

was held whereby c.200 countries (including the US and China which had previously

been opposed to the protocol) signed a treaty to accelerate the complete ban of the use

of hydrocarbons by 2020, and developing countries were given until 2030. China

currently has CFC levels equivalent to those that were present in the 60s and 70s in

the UK 3.

With the use of halofluorocarbons being phased out, all CFCs are currently banned

except for medicinal use only13

. In the US, the use of CFC, HCFC or HFC gasesrequires the technician to pass licensing examinations set by the Environment

Protection Agency. 13

1.5.5. CFC Substitutes

Scientists have developed and are currently developing alternatives to CFCs, to meet

the legislations requirement. CFCs have a variety of uses, primarily as cleaning

agents, fire extinguishing agents, foam, and refrigerants 15.

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The CFC substitutes developed include:

HFC-134a, a chlorine free compound used as a refrigerant with an Ozone

Depletion Potential (ODP see overleaf) of zero 16 .

PhostrEx, the fire suppression agent used in light jets, was developed to be

free of CFCs and is now being sold to other airplane manufacturers 13.

HCFC: the H atom increases the reactivity of the compound, so less is

required for its use. In addition, 95% of the compound is destroyed the

troposphere and never reaches the stratosphere 11 , for example CF 3CH 2F.

Other chlorine-free compounds have been developed as well, and their use

is in rapid growth, especially fluorinated and partially fluorinated

hydrocarbons 15, such as CF 2C12. This requires replacing the chlorine with

fluorine. These compounds do not destroy the ozone layer (doesnt react

with O 3) but unfortunately have a high Global Warming Potential (GWP)

and so contribute to climate change.

Therefore, compounds that are developed today not only have to be chlorine-free but

also have to abide by the Kyoto protocol by having a low GWP 15.

Using models, we are able to estimate this future decrease of atmospheric chlorine

level ( see Figure 12 ) and a complete drop by about 2070 1. The ozone hole itself is

hoped to level off by 2019 and eventually start to decrease by 2050 3.

Figure 11: The ozone hole with the area of the United States superimposed 3

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Figure 12: Past and predicted levels of atmospheric chlorine 3

Although this legislation appears to be taking effect, the lifetime of CFCs is very long

and particularly CF 3Br is very potent at destroying ozone ( see Table 4 : bromine has

10 times the ODP of chlorine). In addition, unlike Cl, Br wont react with methane 1:

reactionnoCHBr

CHHClCHCl

4

34

+

++

Therefore it is unable to form a reservoir compound and difficult to get rid of bromine

once it has entered the atmosphere 1. Therefore it could take quite some time before

the anthropogenic sources (i.e. derived from human activity) of Cl and Br are

removed from the atmosphere.

Table 4: Halocarbon abundances, lifetimes and Ozone Depletion Potentials

Halocarbon Abundance 17 (pptv)

Lifetime 1 (years)

Ozone Depletion Potential 1 (=Ozone destroyed by unit mass halocarbon/Ozonedestroyed by unit mass of CFCl 3)

CFCl 3 280 55 1.0

CF2Cl2 484 100 0.8

CF3Br 2 65 10.0

CH 3CCl 3 158 50 0.1

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Finally, it can be seen that global warming did not cause the ozone hole; however

there are links between the two processes 11 :

CFCs are greenhouse gases

The stratosphere is actually cooling due to global warming, so more PSCs

can be formed, increasing the amount of reactions for ozone depletion.

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2. Air Pollution


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2. Air Pollution

Figure 13: Diagram to show the range of chemicals emitted by natural and anthropogenicactivity, as well as depositions, transport and photochemistry 18

The industrial revolution in the 17 th century instigated the development of urban

conurbations and also caused a rapid increase in anthropogenic emissions causing air

pollution 19 . This lead to heavy, stagnant combustion smog 19 (so named as it is a

portmanteau of smoke and fog 20 ) over cities such as London and caused a variety of

serious heath problems including pulmonary disease and heart failure 19. The smog

contained a mixture of Primary Pollutants emitted directly from the combustion

source, especially soot particles and sulphur dioxide (SO 2). Reductions in these

emissions were made leading to a reduction in combustion smog occurances 19.

In the last century, increasing emissions of oxides of nitrogen and sulphur due to

industrial and domestic combustion have lead to acid rain19

.

NOxVOC

&s

4CH

NOxVOC

&s

ryn

DDepositio

Wet deposition

h

Stratosphere

Troposphere

eaS

VOCsalns

me

&X

s,&

- Naturemissio

Flow of ozone frostratospher

DMSCH 3

Termites, cowdomestic emissionsdomestic ruminants

Industrial Activity

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Since the post-war era of the 1950s, both the population and use of motorized vehicles

has rapidly increased. These emissions caused a hazy photochemical smog 19. This also

causes adverse health problems, such as eye irritations, sore throats, asthma and

respiratory diseases 19. It was found that the component of photochemical smog (and

cause of these ailments) were Secondary Pollutants, made from Primary Pollutants.The main components are ozone and PAN (peroxyacetylnitrate - CH 3C(O)O 2 NO 2)

and are formed from the action of primary pollutants (from car exhausts etc) such as

reactive VOCs and nitrogen oxides, with sunshine 19. Every major city in the world

now experiences photochemical smog 19. From the figure above, it can be seen that the

troposphere today has a complex array of emissions and processes.

2.1. Emitted Pollutants 1

VOCs are volatile organic compounds; these contain a large variety of different

organic compounds both emitted from anthropogenic and natural sources. They

absorb IR radiation, as does methane (CH 4), and so contribute to global warming

and they are therefore greenhouse gases.

o VOCs from anthropogenic sources are mainly from the burning of fuels (such

as in industry, for energy supplies and through the usage of cars). Alkanes are

used as fuels and their combustion can be complete or incomplete, so somelight, unburned hydrocarbons are emitted during combustion, such as through

car exhausts. Incomplete combustion causes emission of CO and complete

combustion emits CO 2. Additionally, the light hydrocarbons in fuel evaporate

when refuelling or storing, and others during combustion. A source of light

alkanes is due natural gas leakage and a source of alkenes is biomass burning.

o Natural sources of VOCs are from vegetation (plants, trees, fungi and algae),

which they emit as pheromones (to ward off predators, to attract insects), to

regulate their temperature or even as antifreeze. The VOCs include

hydrocarbons, CO 2 from respiration and CO.

NOx includes NO and NO 2, this is formed due to high temperatures in combustion

(especially in the combustion of fossil fuels) where nitrogen and oxygen react: N 2

+ O 2 + heat NO x. In addition, there are some natural sources of nitrogen, such

as ammonia from fertiliser and manure 23. This causes the formation of smog and

acid rain.

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SO 2 and particulates are also released through anthropogenic processes, as

combustion of hydrocarbons releases soot and ash and combustion of

hydrocarbons containing sulphur releases sulphur dioxide. These are emitted

through car exhausts, and as pollution from industry. In addition sulphur can be

emitted from natural sources, such as volcanoes, the action of bacteria in soils andlightning 23. These can both contribute to smog and SO 2 contributes to acid rain.

2.2. Removal Processes of Compounds 1

Wet deposition involves the incorporation of species into aqueous media such as

mist, rain, sea, and snow. This therefore has to involve soluble species such as the

following inorganic compounds: HNO 3, H 2SO 4, HCl, HONO and SO 2. VOCs

usually are hydrophobic and therefore insoluble and rarely are lost through wetdeposition.

Dry deposition is removal of species through their adsorption onto air mass.

When air mass comes into contact with water, earth or vegetation the emitted

species can either physisorp (through Van der Waals forces) or chemisorp

(through a chemical reaction). The rate of this determined by the flux through the

atmospheric boundary layer (1 km form the Earths surface 3) the rate of

adsorptions. Generally the species are polar and therefore inorganic such asHNO 3, NO 2, HCl, HONO, O 3 and SO 2. Only very polar VOCs are lost through

this process.

Chemical removal is the removal of VOCs through oxidation. This is mainly

done by the OH radical, but also ozone, NO 3 radicals and even direct photolysis.

This is why the troposphere is said to be oxidising. Through oxidation, it reacts

with the species and eventually H 2O and CO 2 get out water is then rained out (a

subcategory of wet deposition) and CO 2 is a greenhouse gas.o The OH radical is created via the mechanism:

++

++


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(O( 1D)) is created by photolysis. However, as the troposphere sits below the

stratosphere, the air in it is at a higher pressure. This leads to a balance

between concentrations of water vapour and M. At these high pressures the

excited O( 1D) is rapidly quenched by M, however the troposphere also has 10-

50,000 times higher water vapour concentrations than in the stratosphere so asmall amount of O( 1D) reacts with water to form OH radicals.

o The OH radical reacts with VOCs (RH) via the reaction:

O HR RHOH 2++

The rates of reaction (and hence lifetime of RH) increases with increasing

number of Hs as there is a greater chance of collision with . However,with a polar atom in the molecule, such as Cl in CH 3Cl, the reaction is a lot

faster as the Cl is electronegative, inducing a dipole in the molecule and

leaving the Hs a lot more positive so they are more reactive. With alkenes, an

addition reaction occurs:

OH

2222 CH(OH)CH M CHCH OH +=+

2.3. Smog Formation 1

The main ingredient of smog is O 31 which is caused by the action of sunlight on NOx

and VOCs. As discussed earlier, VOCs can react very quickly with the OH radical

and in heavily polluted areas, VOCs are often very prevalent especially aromatic

compounds, alkenes and aldehydes as these react very quickly to form smog 1.

Nitrogen oxides (NOx) create ozone in the troposphere. This is unwanted and harmful

to plants and humans respiratory systems, as well as being a major component of

smog. This occurs due to the following mechanisms 1:

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Without NOx:

destroyedisO

OCOOCO : Net

2OOHOHO

MHOMOH

COHOHCO

3

223

232

22

2

++

++

+++

++

With NOx:

producedisO

OCO2OCO: Net

MOMOP)O(

OP)O( NOh NOOH NO NOHO

MHOMOH

COHOHCO

3

322

323

23

2

22

22

2

++

+++

+++

++

+++

++

Figure 14 3 overleaf shows the complete cycle of how ozone is formed and destroyed

via the action of NOx and sunlight. In urban areas the concentration of NOx and

VOCs are always high, however one doesnt see smog on a daily basis as intensesunlight is required to create the OH radicals and photolyse NO 2 (therefore producing

O3), so clear, still, hot days are ideal for smog formation 1.

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Figure 14: Diagram to depict the cycle of formation and destruction of ozone, determined byNOx

Image courtesy of: T. G. Harrison and D. E. Shallcross, Teacher Update 1 Atmospheric Chemistry , University of Bristol,Bristol, 21 st June 2006.

The graph below ( Figure 15 ) shows how production of ozone - hence smog - varies

with NOx concentration. As NOxs are produced from anthropogenic sources (car

exhausts and industry), their concentration is higher in urban areas than rural:

Figure 15: Graph to show the variation of ozone produc tion (hence photochemical smog) withNOx concentration 1

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At low NOx concentrations, there is more ozone than NOx, so ozone is destroyed

by CO. This typically occurs in a marine environment 1.

At zero net production of ozone (the compensation point 1), the amount of

destruction equals the amount of ozone production.

Above the compensation point there is a linear increase in the production of ozonewith increasing NOx concentrations (as explained by the mechanism above).

This reaches a maximum, and at very high NOx concentrations, there is

retardation of ozone production as radical termination reactions occur 1:

MHNOMOH NO 32 +++

(M is an unreactive species in the air which can absorb excess energy from the

reactants)

So we see lower levels of smog with extremely high concentrations of NOx.

Ozone only lasts on the surface for a few hours, so one can monitor the changes in

ozone levels throughout the day. For example, on a sunny day when NOx levels peak

early in the early morning rush hour, ozone levels increase for a few hours afterwards

and then drop in the evening. However, ozone rises slightly into the troposphere and

remains there for a few months which is an unwanted effect as ozone is a greenhouse

gas 3.

2.4. UK Emissions Today

CO and SO 2 levels have decreased since the 1970s 3 o This is because society has made an effort in cleaning up these pollutants,

through legislations such as the Clean Air Act (introduced in 1956). This act

created zones where smokeless fuels had to be burnt, moved power stations to

rural areas (to reduce urban smog), and required industries and factories to

have tall chimneys to disperse air pollution 21 . Since then, power stations and

factories are required to have filters and catalytic converters in their chimneys.

NOx and VOC levels have stayed almost constant, as although cars emissions

have been cleaned up (through the use and improvement of catalytic converters),

the volume of cars has increased 3

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Society has increased their awareness of pollution and its causes since the

industrial revolution. There are continuing efforts to find greener fuels to reduce

these emissions.

Infrared spectroscopy can be used to monitor air pollution through the use of

mobile Fourier transform spectrometers as the major components (CO, CO 2, SO 2, NO 2 and VOCs) can be detected.

2.5. Catalytic Converters

A catalytic converter treats the exhaust of a car before it enters the atmosphere to

remove sources of air pollution.

The main components of car emissions are N 2 gas (due to the fact that the majority ofair in N 2 gas, so this passes through the cars engine), CO 2 and H 2O (both products of

combustion). As combustion is not always complete, trace amounts of CO, VOCs

(unburned fuel that has evaporated), and NOxs. Besides carbon dioxides Global

Warming Potential, the trace gases are most harmful and causes of air pollution.

A catalytic converter is usually 3-way: it has a reduction catalyst, an

oxidation catalyst and a control system (which monitors the exhaust and

feeds back information to fuel injection system) 22 .

The reduction catalyst is the first stage and uses a ceramic (usually)

honeycomb structure coated with platinum and rhodium 22. It reduces NOx

emissions by 22:

o Adsorbing NO and NO 2 at the catalyst surfaceo The NOx then undergoes a chemical reaction whereby it bonds with the

nitrogen, hence breaking the N-O bond so oxygen is free and bonds with

other oxygen atoms to form O 2. The N then reacts with other N atoms on

the catalysts surface and so forms N 2. This is then desorbed from the

catalysts surface as free N 2 gas.

The oxidation catalyst is the second stage and uses a platinum and palladium

catalyst coated again onto a ceramic honeycomb structure 22. It oxidises

unburned hydrocarbons (VOCs) and CO 22 by lowering the activation energy

for combustion of these reactants with the remaining oxygen supply in the

exhaust.o The catalyst adsorbs CO and the VOCs onto the catalyst surface

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o Free O 2 in the exhaust gas passes over the catalyst and the catalyst

therefore aids the oxidation of the CO and VOCs causing a chemical

reaction to form CO 2.

o This CO 2 doesnt adsorb as well onto the catalyst so is released into the

exhaust.

2.6. Acid Rain

Acid rain is caused by NOx and SO 2 converting to nitric acid and sulphuric acid23 .

Rain is normally slightly acidic anyway, having a pH of 5.5 23 due to the fact that

some acids are dissolved in it from natural sources of nitrogen and sulphur as well

as carbon dioxide. However precipitation in polluted areas or downwind from

polluted air is more acidic than usual due to increased levels of NOx and SO 2.These pollutants are emitted into the atmosphere through combustion of

hydrocarbons or hydrocarbons containing sulphur (the released H 2S reacts with

oxygen during the combustion process: 2222 2SOO2H3OS2H ++ )24 .

Acid)(Nitric HNOOH NO:FormationAcid Nitric

SOHHSO

Hydrolysis HSOHOHSO

in water dissolvesdioxideSulphurOHSOOHSO

:ChemistryPhaseAqueous-FormationAcidSulphuric

Acid)(Sulphuric SOHOHSO

SOHOOHOSO

HOSOOHSO

:ChemistryPhaseGas-FormationAcidSulphuric

32

233

322

22(l)2(g)2

4223

3222

22

+

+

+

+

+

++

+

+

+

25

Thus, both are oxidised by the reactive hydroxyl radical ( see Section 2.2 for how

is created). In the presence of water vapour, the sulphur trioxide (SO 3) is

rapidly converted to sulphuric acid

OH25. In clouds, liquid droplets of water react

much more rapidly with sulphur dioxide 25.

These acids are both dissolved into water, precipitated down to earth, and the pollutants may be deposited through dry deposition closer to their source onto

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vegetation and soils, where the above reactions occur to create acids 23. If it is

dissolved into clouds, the acids may travel a long way, even hundreds of

kilometres before it falls 23 therefore pollution recognises no boundaries and acid

rain caused by UK emissions are known to have fallen in Norway and devastated

the forests. In fact, the UK accounts for at least 16% of Norways acid rain26

.

Effects of Acid Rain

of rivers and lakes and so can destroy the ecosystems,

vegetation and organisms within them. pHs below 5 will stop fish eggs from

ria in the soil 27.

diseases such as cancer, bronchitis, emphysema and

The increased acidity

hatching and below that can kills even adult fish 27 . So as acidity increases, the

biodiversity of lakes decreases 27. Acid rain has made certain fish and species of

insects extinct27

. Changes to the soil pH can harm plants and denature

enzymes and bacte

Image taken from: European Environment Agency Websitehttp://reports.eea.europa.eu/2599XXX/en/page009.html

Acid rain can slow the growth of vegetation and forests 27.

There is an increase in the rate of people obtaining lung

asthma 23. This is thought to be caused by the inhalation of

small particulate matter with an effective diameter of

m01 or less (PM10s); including sulphur 23 so acid rain

may be a contributing factor to these human health problems.

Limestone is easily dissolved by acids:

H O

Image taken from:http://upload.wikimedia.org/wikipedia/commons/thumb/5/54/-_Acid_rain_damaged_gargoyle_-.jpg/800px--_Acid_rain_damaged_gargoyle_-.jpg

COCaSOSOHCaCO 224423 +++

So buildings and monuments have becomeeasily eroded 26.

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Reducing Acid Rain

Efforts are being made to reduce acid rain by removal of these nitrogen and sulphur

based pollutants at their source. Sulphur dioxide can be removed from flue gases

using calcium oxide:

32 CaSOSOCaO +

This is then easily converted to CaSO 4, known as gypsum24. Gypsum is a mineral

with many uses: it is an ingredient in plaster (of dry walls) and fertilisers 28 . Most of

the gypsum in the EU market is made from flue gas desulphurisation 24. Through the

enforcement of this process, the United States (for example) has seen a 33% decrease

in SO 2 emissions between 1983 and 200224

.

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3. Global Warming


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3. Global Warming

3.1. Greenhouse Effect

This is a process whereby the whereby the reflection of infrared (IR) radiation by the

Earths surface and incoming IR radiation from the sun is absorbed by greenhouse

gases in the troposphere. Solar radiation reaching the Earths surface is mainly visible

and UV light. The earths surface (vegetation, land and oceans) absorbs incoming

visible and UV light, which heats it up. It then re-radiates 4% of this as heat in the

form of IR radiation 29 . The reason why the earth doesnt rapidly drop in temperature

at night is because greenhouse gases in the troposphere (i.e. the part of the atmosphere

closest to the Earths surface) absorb the radiated IR radiation in the IR window (the

IR region of the spectrum where these gases show strong absorptions) and re-emit it

in all directions as heat, so some of this heat is transferred to the Earth and heats it up.

In addition, when the gases absorb IR radiation, their vibrational modes are excited,

so they vibrate more vigorously and are more likely to collide with other molecules,

transferring their energy. This increases the kinetic energy of other molecules and

raises the average temperature of the troposphere. 60

Figure 16: Figure to show the proportions of radiation emitted, t ransmitted and reflected by theatmosphere and Earth's surface 29

3.2. Climate Change

Climate is the characteristic weather of a region averaged over some period of

time 1. So a change in climate is not the same as a change in weather (which can vary

on a daily basis). Climate change today is referred to as the change in climate that has

been closely observed since the early 1990s and is thought to be caused by global

warming30

.

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3.3. Global Warming

Global warming is a controversial topic that has caused intense and often emotional

debate since the mid 1980s 31 . It refers to the recorded increase of the mean surface

temperature of the Earth, which is thought to be due to an increase in the

concentration greenhouse gases in the atmosphere due to human activity 31. There has

almost definitely been a 1 degree temperature rise in the Earths surface temperature

over the past 100 years 1.

3.3.1. Greenhouse Gases and How They Work

These greenhouse gases include H 2O, CO 2, CH 4 and NOx molecules, and are so-

named because they absorb IR radiation and re-emit the heat in all directions

thereby increasing the temperature of the atmosphere. NB, O 2 and N 2 are not

greenhouse gases since in order to absorb IR radiation there must be a change in the

dipole moment, and O 2 and N 2 are symmetric and so not stretch or bend would cause

a change in dipole moment. The IR radiation is of the correct frequency to be

absorbed by the electrons in the C=O bonds in carbon dioxide, O-H bonds in water

and C-H bonds in methane, causing them to vibrate, bend, rock, scissor and twist (for

example). The electrons have become excited, hence promoting the electrons to

higher vibrational energy levels. When the electrons return to their ground state, they

re-emit the energy with a frequency equal to the frequency of energy gap between the

two levels. 32

The Greenhouse Effect of a given gas how much it heats up the Earths

atmosphere - is dependent upon: 48

Its atmospheric concentration: the greater the concentration of the gas, the more

molecules there are to absorb IR radiation.

Its ability to absorb IR radiation: some gases absorb and re-emit IR radiation more

strongly than others.

3.3.2. Evidence for Global Warming

The carbon dioxide and methane concentrations in the atmosphere are increasing

and they have been increasing rapidly since the 1800s.

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Figure 17: Graph to show the increase in carbon dio xide concentration in the troposphere from1967-1997 1

Methane (CH 4) levels have been increasing exponentially from the 1800s

onwards. This is probably due to thawing of permafrost which contains trapped

methane, increased rice cultivation (methanogenic bacteria live in rice paddies),

leaking of natural gases from pipelines and during transport, and increasing

ruminants 1. However, some of this may be offset by the destruction of wetlands

(hence methanogenic bacteria 1 so it is a balance of the two and the former must

be dominating.

Figure 18: Graph to show the variation in methane concentrations since 1000 A.D. 1

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The concentration of CO 2 was constant until the industrial revolution, when a

sudden increase was observed. This shows it has increased due to the combustion

of fossil fuels 1 as CO 2 is produced in combustion and the industrial revolution

saw a rapid increase 1 in the use and combustion of fossil fuels for power.

Figure 19: Graph to show the change in atmospheric carbon dioxide co ncentrations 1006-2002A.D. measured from Ice Core Data and from 1950s as a Direct Measurement 1

Ice Core Data

DirectMeasurement

INDUSTRIALREVOLUTION

Our global consumption of fossil fuels is still increasing today, as are the CO 2 and

CH 4 concentrations. This coincides with the 3 hottest years on record have

occurred since 1998, and 19 of the 20 hottest years on record have occurred since

1980.

In summary, the carbon dioxide and methane levels are higher than anytime in the

past 1 million years and potentially the past 30 million years 1. Although the levels

are probably in no way close to the highest levels in Earth history, the difference

here is that we know the rate of change of these levels is faster than it ever has

been by a large difference (millions of years versus 200 years). In addition, there

has been an (almost) certain global temperature rise of 1 degree over the past

century, despite of the high heat capacity of the oceans.

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Figure 20: The Combined Global Land and Ocean Surface Temperature Record from 1850 to

2007 33

This graph further depicts the marked increase in temperature over time: 2007 was the8th hottest year on record, 1998, 2005, 2003, 2002, 2004, 2006 and 2001 respectively

were the top 7 33. What is clear is the difference between anthropogenic and natural

climate change. There are variations in the climate, and CO 2 and CH 4 levels over

hundreds of thousands of years. However we have never before seen fast a change

over such a short period of time. The Intergovernmental Panel on Climate Change

(IPCC) was set up to evaluate the risk of climate change and make suggestions to

attenuate those risks. The panel concluded:

" Most of the observed increase in globally averaged temperatures since the mid-20th

century is very likely due to the observed increase in anthropogenic greenhouse gas

concentrations. "34

"From new estimates of the combined anthropogenic forcing due to greenhouse gases,

aerosols, and land surface changes, it is extremely likely that human activities have

exerted a substantial net warming influence on climate since 1750. "34

However, some scientists, such as the European Science and Environment Forum,

disagree that the observed climate change is caused by human activity as the climate

historically has been shown to fluctuate, prior to the onset of industry in modern

times. In addition, the models (and assumptions within them) used has caused

disagreement. 30

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3.3.3. Global Warming Potential

The Global Warming Potential (GWP) of a greenhouse gas is the ratio of global

warming per unit mass of the greenhouse gas to the global warming of CO 2 per unit

mass 35 . It is therefore a measure of the relative strength of the greenhouse gas in

causing global warming.

Table 5: Table to show the GWP and lifetime in the atmosphere of selected greenhouse gases

Global Warming Potential 36 Greenhouse Gas

Lifetime

(years) 35 20 Years 100 Years 500 Years

Carbon Dioxide 1 1 1

Methane 12 62 23 7

Nitrous Oxide 114 275 296 156

CFC-11 35 55 4500 3400 1400

CFC-12 116 7900 8500 4200

3.3.4. Carbon Neutral, Biofuels and Carbon Footprint

Carbon neutral refers to an activity that has no net annual carbon (greenhouse gas)

emissions to the atmosphere. For example:

Bio-ethanol is in theory carbon neutral, as it is made from growing crops, mainly

corn and sugar cane, which takes its carbon from eh carbon dioxide in the air. This

carbon then is used to from the ethanol. When combusted the ethanol forms

carbon dioxide again so there are no net emissions. It produces the same amount

of CO 2 as it takes in from photosynthesis when growing. However, energy is

required to grow the crops (plant and harvest) and then to convert them to ethanol.

Fertiliser and pesticides are also required to grow the crops, however, they are

pollutants. In addition, the crops required for bio-ethanol could compete for land

with other food crops and grazing land for animals, as well as destroying natural

habitats and reducing biodiversity. It could even encourage deforestation. 37

It remains unclear if the total carbon footprint of bioethanol is actually less

than that of fossil fuels

The same principles above can be applied for carbon-neutral petrol and bio-diesel,which is a mixture of methyl esters of long chain carboxylic acids.

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Bio-diesel (again, carbon neutral) is made through a transesterification reaction of

vegetable oils with methanol and a catalyst, such as potassium hydroxide 38 . The

source of the oil is usually rapeseed, palm or soybean. In the U.K. rapeseed is by

far the largest source of oil for producing biodiesel. 39

The three main methods of producing biodiesel are 39:

Base-catalysed transesterification of the oil Most common as most cost-

efficient, requires the lowest temperatures and has 98% conversion

Acid-catalysed transesterification of the oil

Reaction of the oil to from its fatty acids, and then reacting on to form

biodiesel

The reaction is as follows 39, with the esters formed being the biodiesel itself.

Hydrogen is also a carbon neutral fuel it can be used in hydrogen fuel cells,

which uses oxygen as the oxidant.

Methanol can be made by reaction of carbon monoxide with hydrogen. CO and H 2

are collectively called syngas and commercially produced by reacting methane

with water or a limited supply of oxygen.

OHCH2HCO 3

OAlZnO,Cu,

2

32

+

The modern-day catalyst for this reaction produces high selectivity and is a

mixture of copper, zinc oxide and aluminium oxide, at 50-100 atm of pressure at

250 0C. 40 This is a carbon neutral process as any CO produced when combusting

natural gas can be reclaimed to produce methanol so there are no net carbon

emissions into the atmosphere.

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Biofuels

A biofuel is a fuel made from a living things or the waste produced by them, and so is

renewable and potentially carbon neutral 41 . However this is debatable for the reasons

given in the argument for bio-ethanol. A second-generation of biofuels is begin

developed, which will use the cellulose found in plants and will potentially be more

efficient, requiring fewer plants and fuels can be created from a greater range of plants

and plant waste 41, reducing the loss if biodiversity that production of biofuels causes.

The living things that can produce biofuels include 41:

Wood

Biogas (methane) from animal excrements

Ethanol and diesel made form plants and plant waste

Carbon Footprint

A Carbon Footprint is a measure of the impact our activities have on the

environment in terms of the amount of greenhouse gases we produce. It is measured

in units of carbon dioxide. 42

3.3.5. Controlling Global Warming and the Kyoto Protocol

As can be seen from the above discussion, the emissions of greenhouse gases and

pollutants from anthropogenic sources leads to increased atmospheric concentrations

of these gases and hence causing ozone destruction, air pollution, acid rain, and

almost certainly global warming.

Therefore, it is important that we as a society control these emissions to minimiseclimate change resulting from global warming. Possible solutions to reduce the CO 2

levels and emissions are:

Carbon capture and storage: this involves the removal of waste carbon dioxide.

The CO 2 can either be captured post-combustion of fossil fuels from power

stations by removal from the flue gases. The technology required for this is

already in place for other applications. It can also be removed pre-combustion by

separating natural gas (CH 4) into H 2 and CO (collectively called syngas) through

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partial oxidation. Then the CO is further oxidised through the water-gas shift

reaction ( 222 HCOOHCO ++ ) into CO 2, which is then captured. The H 2 then

goes on to be used as a fuel in combustion and is cleaned of carbon. The CO 2 can

be transported through corrosion resistant pipelines which are already in place

for the transport of oil and natural gas. It can then either be converted into a liquidto be injected deep into the oceans; or stored as a gas in empty oil and gas fields

and saline formations; or by reacting it with metal oxides; it will form stable solid

carbonate minerals. 43

Encouraging the more economical use of fuels; such as turning off lights when not

in the room and turning off computers and TVs when not in use, reducing the

amount of vehicles on roads by promoting public transport and by posing green

taxes companies might be encouraged to combine lorry loads. Through the use of alternative fuels, such as hydrogen, wind power, solar power,

wave power, HEP and tidal power; we would be burning fewer fossil fuels and

therefore reducing the amount of CO 2, VOCs and NOxs emitted into the

atmosphere.

By planting more vegetation there would be increased photosynthesis which

would remove carbon dioxide from the atmosphere.

Kyoto Protocol

Our progress in reducing greenhouse gas emissions can be enforced and monitored

through initiatives such as the Kyoto protocol.

The Kyoto protocol is an agreement signed in 1997 by at least 55 developed

countries pledging to cut greenhouse gas emissions to 5% below 1990 levels by

2008-2012. 44

The greenhouse gases they aim to reduce are: CO 2 (carbon dioxide), CH 4

(methane), HFCs (hydrofluorocarbons), PFCs (perfluorocarbons) and SF 6 (sulphur

hexafluoride). 44

Each country had its own specific target, for example EU countries pledged to cut

emissions by 8% and Japan by 5% .44

It does not require developing countries to cut emissions. 44

The US has currently not agreed to the protocol, claiming it will significantly

affect their economy. 44

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However many sceptics say the agreement is almost futile without US support as

they are the worlds largest emitter of greenhouse gases, in addition to the fact

developing countries (increasing polluters as they are currently going through

their own industrial revolution) do not have to cut emissions. Additionally, the

aim to reduce greenhouse gases by 5% is claimed to be no way near enoughaccording to many climate scientists, and about 60% cuts are required to avoid the

risks global warming presents. 44

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4. Recycling


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4. Recycling

4.1. Why Recycle

The worlds resources, such as metals and oil, are running out and finite (non-

renewable), so in order to continue to make use of these valuable substances waste

prevention has to be considered. There are also other social, economical and

environmental problems posed by waste such as where it is stored, inefficient use of

resources, the expense of disposal and creating new products from raw materials,

health risks and risks to the environment 61. For example, landfill sites release

greenhouse gases (especially methane) and other toxic gases, waste can turn toxic and

local habitats are destroyed. By not recycling wood-based products deforestation

increases 49, this leads to an acceleration of global warming and destruction of

ecosystems. To help deal with these issues, society, industry and governments

encourage people and companies to reduce, reuse and recycle their waste and products

they no longer need. There is an ongoing effort to change to renewable resources and

to reduce waste.

Recycling is defined as 45 :

A resource recovery method involving the collection, separation, and

processing to specification of scrap materials and their use as raw materials

for manufacture into new products.

Image taken from: http://www.unpluggedliving.com/wp-content/uploads/2007/08/recycling-image-small.jpg

There is a widely-accepted hierarchy for waste disposal 61 as depicted in Figure 21 . As

can be seen the most preferred solution is prevention so not to use that material, or

reduction of its use. Disposal is the least favoured option as it doesnt make use of any

of the materials properties.

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http://www.unpluggedliving.com/wp-content/uploads/2007/08/recycling-image-small.jpghttp://www.unpluggedliving.com/wp-content/uploads/2007/08/recycling-image-small.jpghttp://www.unpluggedliving.com/wp-content/uploads/2007/08/recycling-image-small.jpg


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Figure 21: Waste Disposal and Prevention Hierarchy

Image reproduced Courtesy of Sligo County Council

The use of renewable resources, energy recovery and recycling can contribute to the

more sustainable use of materials:

Renewable resources can be replenished by natural processes and the rate of

replenishment is equal or greater than the rate of consumption 46 . They often

do not contribute to global warming or are far more environmentally

friendly. For example, in using plant-based substances such as wood to make

wood based products, the trees can be replanted which is essentially a

carbon neutral exercise. In terms of energy, solar energy, tidal energy,

biomass, HEP and wind power are all examples of renewable energy. The

use of renewable resources leads to the more sustainable use of materials as

the resources can be used indefinitely.

Energy recovery also leads to the more sustainable use of materials, as it

ensures the usefulness of even waste products is exploited. For example, if

waste polymers are incinerated, the energy released can be used to drive a

turbine and contribute to the national grid.

Recycling allows for materials to be made into new products, therefore

making use of the substance the product is made from. There is increasingly

greater use of recycling of manufactured materials such as plastics, glass and

metals.

In addition, the chemical industry should endeavour to use industrial

processes that reduce waste products, hazardous chemicals (especially

pollutants or greenhouse gases) and maximise atom economy. If any waste

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products are produced, they should be able to be degraded into safe

substances in the environment, or recycled.

Atom economy is also important in waste prevention. Atom economy is how many

reactant atoms end up in the desired product as compared to waste products and other

by-products 47 . Percentage atom economy is defined as:

100 UsedReactantstheallof WeightMolecular

ProductDesiredof WeightMolecularEconomyAtom% =

This is a more useful parameter than yields when considering green chemistry.

Although it is important to maximise the yield, atom economy is a better way of

measuring efficiencies between different reactions that have the aim of forming the

same product 61. It can provide an extra diagnostic tool in measuring reaction

efficiencies and can sometimes compensate for low yields or poor selectivity. The

chemical industry is encouraged to use this concept when deciding on reaction type

for the production of polymers and medicines. For example, if a lot of CO 2 is

produced as a by-product with a low atom economy then this is a disfavoured

reaction.

Catalysts can be used to lower the energy demand of a reaction, and reduce CO 2 emissions from burning of fossil fuels. 48 Catalysts can be used to make a reaction

have a better atom economy or allow a different reaction to be used with fewer waste

products and better atom economy.

4.1.1. Household Waste

In 2003/04, UK households produced 30.5 million tonnes of rubbish, and only 17% of

that was recycled. This is low compared to some other EU countries: some recycle

50% of their household waste. 60% of rubbish that goes into household bins could be

recycled and up to 50% of waste in household bins could be composted. 49

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Figure 22: Pie Chart to Show the Average Constituents of Household Waste 50

Paper and Board18%

Dense Plastic 4%

Plastic Film 3%

Garden Waste21%

OtherCombustibles

1%Kitchen Waste

17%

Fines 3% Soil and OtherOrganics 3%

Nappies 2%Wood 5%

Glass 7%

Miscellaneous Non-

Combustibles5%

Metal Packaging3%

Scrap

Metal/WhiteGoods 5%

Textiles 3%

4.1.2. Aluminium and Steel

In the UK, aluminium and steel are amongst the most common metal used. Despite

the fact that per capita consumption of steel has dropped since the 1970s, the

consumption of aluminium is still growing 51 . Global production of aluminium

averages to about 24 million tonnes per year and for steel 1.05 billion tonnes in 2004,

an increase on 2003 of 8.8% (and excluding china an increase of 4.5%) 51. This

enormous production volume and requirement for aluminium and steel clearly causes

waste disposal issues when the metal products are no longer needed. Waste metal

makes up 8% of household waste, yet only roughly a third of metal waste is currently

recycled 51. An advantage of recycling metals is that they never loose their properties

no matter how many times they are recycled.

Table 6: Advantages and Disadvantages of Recycling versus Extracting Metals

Pro-Recycling Scrap Metal Pro-Extraction of Metals

Metal ores are non-renewable and therefore will eventuallyrun out recycling will prevent this

Sometimes through the extraction of metals one can obtain amuch purer metal than one could through recycling

Less disruption to the landscape as not quarrying. Whenquarrying for metals it makes large unsightly scars on thelandscape. In addition, it can pollute rivers, and produces a lotof dust which can pollute the air; contributing to globaldimming and respiratory diseases 52

When considering the energy required to recycle the metal,one is not considering the energy required to collect all thescrap metal from different recycling points (e.g. recycling

banks and kerb-side)

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Extracting metals can also damage the habitats and localecosystem of where the extraction is taking place

Therefore, the energy required to transport all the scrapmetal to the recycling plant, and to sort the metals mayrequire more than extraction of metals

Ores are often located in remote mountainous regions 52, so itis expensive to:

Transport the machinery to the region Transport the ore to the extraction plant Hire workers and house them, as not many people would

live in the area and potentially there is nohousing/infrastructure

It would also be difficult to find workers to extract themetals

It is difficult to organise and implement an efficient recyclingscheme as it requires households, industry and companies toall contribute to the UKs new metal supply. Differentcouncils organise this in different ways, operating recycling

banks or kerb-side pick up. However, this can be inefficientwith not all the households metal being recycled and difficultto separate the waste

Reduces the waste entering landfill sites: fewer/smallerlandfill sites are required as metals are not going into it. Thisalso reduces disposal costs 53 . It also reduces the number ofdumped cars 53

Not using up valuable resources: saving the metal ores andsaving resources and chemicals required in the manufacturing

process 53

In extraction, in order to obtain the pure metal from its ore itneeds to be reduced. By recycling, one it not using upexpensive reducing agents, such as titanium metal. If carbon(as coke or charcoal) is used, this is using up another finiteresource which also is polluting. If reducing the metal throughelectrolysis this is also expensive

The recycling process creates jobs 53

One of the major deciding factors is how much energy isrequired to recycle compared to how much energy is used inextracting the metal: in almost all cases, it requires much lessenergy to recycle the material as can be seen from theexamples of steel and aluminium below

All steel cans are 100% recyclable 51

All steel products can be recycled indefinitely (apart fromaerosol cans) so waste disposal problems are reduced

Recycling 1 tonne steel has the following environmental

benefits51

: Saves 1.5 kg of iron ore Saves 0.5 kg of coal Saves 40% of water usage Carbon dioxide is emitted when making steel from iron

ore. As this is a greenhouse gas, this contributes to globalwarming and climate change. Recycling 1 tonne of steelscrap saves 80% of the CO 2 emissions produced

Saves 1.28 tonnes of solid waste Reduces air emissions by 86% (as not processing steel

from iron ore) Reduces water pollution by 76% Saves 75% of the energy needed to make steel from iron

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ore

Recycling 1 tonne aluminium has the followingenvironmental benefits 51:

Saves 6 tonnes of bauxite (aluminiums ore) 51 Saves 4kg of chemical products, as they are not required

to extract aluminium from its ore Produces only 5% of the CO 2 emissions compared with

extracting the metal Aluminium can be recycled indefinitely, as reprocessing

does not damage its structure. Aluminium is the most cost effective material to recycle Saves 95% of the energy required to extract aluminium

In the extraction of copper the following damaging environmentaleffects occur:

The waste from crushing has to be removed The land where the open mine is becomes devastated The waste from froth flotation, called tailings, has to be

removed Sulfur dioxide from smelting can cause acid rain 52 Electrolysis is re quired to extract the copper which is an

expensive process 52

Scrap iron can also be use d in a displacement reaction to extractaqueous solutions of copper 54 . This is advantageous as:

A lot less energy is required than the traditional method ofhigh-temperature reduction of copper oxide with carbon saving money and fossil fuels.

CO 2 is not being formed - which would be released into theatmosphere, contributing to global warming - from thereduction and from using fossil fuels for energy to heat up thereaction mixture for the reduction

Scrap iron is reused and so isnt immediately taking up spacein a landfill site

Issues Involved in the Recycling of Iron and Steel

The following steps are taken when recycling scrap metals:

Collection of scrap metals: Metals are either collected kerbside from

household waste or at recycling collection points 56. Here, people are asked to

separate their waste into types (paper, metal and glass). All the waste metal is

then transported to a central recycling plant.

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Images taken from: http://www.highpeak.gov.uk/environment/recycle/locator.asp and http://www.recycling-guide.org.uk/

Cleaning by incineration: The scrap metal has to be cleaned as it will often

contain dirt, dyes, inks, coatings and other impurities on its surface. For

example in metal packaging, the label is often printed onto the metal. This is

done through incineration : where the scrap metals are heated to very high

temperatures (850-1100 0C) as this is when the hydrocarbons and organic

impurities on the metal is destroyed as well

as odorous gases and dioxins 55 . Aluminium

foil will oxidise in the incinerator releasing

energy 51. This energy drives a turbine to

produce electricity, and in Ireland for

example the hot water from the heat

exchanger is used for district heating 55.

Aluminium cans will melt and fall to the

bottom with the ash. This is easily separated once it has cooled and re-

solidified 51. The ash can then be used as part of the materials required for road

construction 55.

Figure 23: How Incineration Works 55

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Sorting the metal by magnetic properties: Scrap metal is either ferrous or

non-ferrous. Ferrous means it contains iron (and so is magnetic) so this

includes iron and steel. Non-ferrous scrap metal is everything else; for

example, aluminium, nickel, copper, lead, and precious metals. 51 This

magnetic property (they are ferromagnetic or permanent magnets) of ferrousmetal allows the two groups two be easily separated and sorted: giant magnets

are used to attract ferrous scrap metal 56 (iron and steel) and the non-ferrous

metal (and other waste) is left behind for further separation. This allows the

iron and steel to go on and be easily cleaned by the incinerator (if it hasnt

already) and re-melted to turn it into ingots (large blocks) of iron or steel 49.

Images taken from: http://www.wasterec.co.uk/metals.html

Adjusting the composition of new steel: the molten iron is analysed just

before being re-added to the furnace. If the composition of the steel has to be

changed, the oxygen supply (how long and how much) is altered, and

sometimes some pure metal is added in small amounts to alter the

composition 57 , as it can oxidise the different components in steel.

Scrap is used to adjust the temperature of the furnace: To decrease the

temperature of the molten metal in the furnace, more scrap iron is added,

which cools it down. To increase the temperature maybe increased by

increasing the oxygen supply passing over the burners, or adjust the

hydrocarbon fuel supply to the burners or adjusting the temperature of the

regenerated heat from the checkers . 58

Thereafter, the molten

iron or steel is allowed to

cool into ingots and sent

to mills where the ingots

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are rolled out into large sheets of steel or iron. This gives the metal greater

flexibility and strength 49. From this, it can be remoulded into its required

shape to make new metal products.

Images taken from: http://img.alibaba.com/photo/50386658/Stainless_Steel_Ingots.jpg and

http://www.turkeyfryerexpress.com/images/BC1102.jpg

4.1.3. Plastics and Polymers

Plastic is in prevalent use globally; in the UK alone 275,000 tonnes of plastic 49 are

consumed annually (this is about 15 million bottles per day 49). In addition, global

use of plastic is increasing year on year: in Europe for example the annual increase is

4% 49. There is a severe need to recycle plastics:

Plastics are made from hydrocarbon

polymers, which are made from crude oil.

Crude oil is a finite and increasingly

expensive resource, so it will eventually run

out. It is therefore essential to recycle

plastics instead of disposing of them in a

landfill site as it will allow us to use crude oil more sparingly now; in addition

it allows us to make use of plastics even when the crude oil supplies are

exhausted.

Plastics can take 500 years to decompose 49, so it uses up space in a landfill site

and is unsightly. Recycling plastics is the obvious solution to this.

Image taken from: http://practicalaction.org/practicalanswers/product_info.php?products_id=190

Disposal of Polymers

Polymers (including polyalkanes) have many advantages, they are chemically inert,

non toxic as solids, impenetrable to bacteria, waterproof (such as plastics), easy to

mould and process, economical, non-biodegradable so can last a long time, thermal

insulators, electrical insulators, have high strength, can be flexibility, have low

friction, rigid and are of low weights (which is useful for example in car

manufacturing as plastics are lighter than steel and other metals so the car has a lower

weight which causes a large reduction in fuel consumption i.e. an environmentaladvantage) 59 .

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