1
Ozone Conference
Teachers Notes
Knowledge and understanding
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The formation of oxygen as the Earth’s atmosphere evolved resulted in the
development of an ozone layer
This filtered out harmful ultraviolet radiation from the Sun allowing the
evolution of new living organisms
The high temperatures produced by burning fuels can cause nitrogen and
oxygen from the air to react, forming nitrogen oxides
Nitrogen oxides can harm plants and animals directly
Ultraviolet radiation can pass through the skin to deeper tissue
High doses can cause normal cells to become cancerous
When supplied with appropriate information you should be able to use your
scientific knowledge to weigh evidence and form balanced judgements about
some of the major environmental issues facing society.
Introduction
In this Brief students attend a conference on the causes, monitoring and
consequences of ozone formation in the troposphere and ozone layer depletion in
the stratosphere. The first session is on ground-level ozone, where conference
delegates hear three papers. They split up into groups to discuss the papers and
report back to a plenary session. The second session is on the ozone layer, where
they repeat the format of session 1.
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Route through this Brief
Introduction to Session
1
Paper 1
Paper 2
Paper 3
Discussion
Plenary
Data activity
Introduction to Session
2
Paper A
Paper B
Paper C
Discussion
Plenary
Data activity
Conference
report
IBSE links
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Using scientific ideas and models to explain phenomena and developing them
creatively to generate and test theories
Obtaining, recording and analysing data from a wide range of secondary
sources and using their findings to provide evidence for scientific explanations
Using appropriate methods, including ICT, to communicate scientific
information and contributing to presentations and discussions about scientific
issues.
The activity will also provide opportunities for students to:
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Research, discuss and develop arguments
Use real-life examples as a basis for finding out more about science
Recognise the importance of sustainability in scientific and technological
developments.
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Prior knowledge
Before attempting this Brief, students should have some knowledge of chemical
bonding and oxidation reactions and an ability to balance simple chemical equations
would be useful. Students should be aware of the electromagnetic spectrum and the
place of ultraviolet radiation and visible light within it.
Running the activity
A. Students could work in a number of groupings during this Brief. Suggestions
are:
Setting the scene
Preparing summaries of
papers
First session papers
Experiments and
investigations
Discussion groups
Plenary session
Data activity
Second session papers
Discussion groups
Plenary session
Data activity
Conference report
Whole class; teacher-led
Threes, fours or fives
Individuals or pairs
Whole class, teacher introduces
session, groups of 3 or 4 pupils
prepare summaries of papers, 3
pupils deliver papers, rest of class
takes notes
Fours or fives (not the same groups
as those preparing the summaries of
the papers)
Whole class, teacher sums up
Individuals or small groups
Whole class, teacher introduces
session, groups of 3 or 4 pupils
prepare summaries of papers, 3
pupils deliver papers, rest of class
takes notes
Fours or fives, different from the 2
above
Whole class, teacher sums up
Individuals or small groups
Individuals or small groups
Note: Other strategies may be preferred. For example, for Session 1, the whole
class splits into groups – each one tackling one of the three papers (paper 1, 2
or 3). This could be followed by discussion. A similar approach could be taken
with Session 2, with students working on paper A, B, or C.
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B. Timing
The Brief should take about 4 hours to teach. The report writing can be set as
homework.
C. Activities
 The teacher should issue the students with the Student Activity sheet which
outlines the activities and can act as an outcomes checklist. This provides a
summary of what they should produce as they work through the activity and
also acts as a checklist for students to monitor their own progress.
 The teacher sets the scene by telling the students they will be presenting
papers at the ‘Ozone conference’. First, however, they must carefully read
‘their’ paper and then make summary notes for the presentation. These must
be precise and accurate so that other student delegates can understand and
contribute to the discussions which will follow.
Preparing the summaries of the papers
There are six papers to be delivered at the conference. It is suggested that the class
be split into 6 groups, one group per paper, to summarise their allocated paper as
concisely as possible. This process is to provide a sort of abstract of each paper.
The summary should be written on a poster for display during the relevant session.
It is intended that these summaries could be used by the rest of the class to make
notes. Each group should choose someone to deliver the paper at the session. The
chosen speaker can read out the paper, or make her/his own version of it. Either
way, the speaker should rehearse beforehand, perhaps in front of the group, to
practise delivery. Each group as a whole should prepare any illustrations that will be
used in the talk in the form of PowerPoint slides.
First session
This session is on tropospheric ozone. The paper Introduction to the 1st session
is a general introduction to the topic, pointing out that ground-level ozone is harmful
to us, but the ozone layer in the stratosphere protects us from ultraviolet radiation.
This paper is intended for the teacher, who should deliver it or summarise the
content at the start of the session.
The 3 papers delivered by elected students are:
1. The formation of ozone in the troposphere
2. Monitoring ozone levels in Europe
3. Effects of ozone on humans, vegetation and materials
The class should take notes or copy out the summaries as these talks are delivered.
The summaries should also be available, possibly as posters, for consultation
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throughout the discussion session. The class splits into groups to discuss the
content of the papers and to make recommendations for further action to reduce
ozone levels across Europe. This should take about 20 minutes. The class reassembles for a plenary session. Each group reports the recommendations
formulated in the discussion session and the teacher summarises these on a
PowerPoint slide or interactive whiteboard.
Note: the first paper simplifies the role of NOx gases in ozone formation. Nitric
oxide (NO) actually converts ozone to 02. The reaction is:
NO + 03
NO2 + O2
Its effect is overwhelmed by that of NO2, and so it is not mentioned in order to avoid
undue confusion.
Second session
The format is similar to that for the first session. The paper Introduction to the 2nd
session provides a brief explanation of how ultraviolet radiation causes ozone to
form. In fact, free oxygen will react with dioxygen molecules only if other molecules
are present to take up the kinetic energy transferred in the reaction. These other
molecules are usually N2, but they can be anything. This paper is intended for the
teacher to deliver. The 3 papers delivered by elected students are:
A. Monitoring ozone depletion layer
B. The causes of ozone depletion
C. The consequences of ozone depletion
This session proceeds with group discussions, a plenary session and a summary by
the teacher, as before.
The group discussion following the delivery of the papers should focus on what
action should be taken to prevent the ozone layer from being depleted any
further.
In both sessions, students should be aware that any recommendations they make
have economic and social consequences. The alternatives to CFCs are expensive
and there are certain applications for CFCs and halons that don’t have alternatives.
If students decide that drastic reduction in private motor traffic to reduce ground level
ozone in cities is the answer, there must be provision for alternatives. There would
be opposition from all sorts of pressure groups, and there are economic implications
for the oil industry, motor industry, etc and this would mean job losses.
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Ozone Conference
Student Activity Sheets
Setting the Scene
In this activity you will be attending a conference on ozone. You will have short talks
and you may be selected to make a presentation about ground level (tropospheric)
ozone and about the ozone layer (stratospheric ozone. You will also take part in
discussions on how to tackle the problems associated with ozone in these two
regions of the atmosphere.
Science you will learn about in this activity:
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



The formation of oxygen as the Earth’s atmosphere evolved resulted in the
development of an ozone layer
This filtered out harmful ultraviolet radiation from the Sun allowing the
evolution of new living organisms
The high temperatures produced by burning fuels can cause nitrogen and
oxygen from the air to react, forming nitrogen oxides
Nitrogen oxides can harm plants and animals directly
Ultraviolet radiation can pass through the skin to deeper tissue
High doses can cause normal cells to become cancerous
When supplied with appropriate information you should be able to use your
scientific knowledge to weigh evidence and form balanced judgements about
some of the major environmental issues facing society.
Outcome Checklist
You will attend a conference on ozone in the troposphere and stratosphere. You will
take part in presentations and discussions about papers in each session of the
conference. You will also use information from ozone monitoring stations to carry
out one or more data handling investigations. You should make sure you produce
the following items as you work through the activity:
Session 1
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Summary notes on the papers and recommendations for action to reduce
ozone levels across Europe
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Session 2
Summary notes on the papers and recommendations for action to prevent ozone
layer being further depleted
Conference report
A brief report based on summary notes and recommendations.
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Ozone Conference
Introduction to the 1st session
What is ozone?
Almost everyone has heard of the ‘ozone layer’, but many people do not know where
it is and why it matters. Fewer still could answer the question, ‘what is ozone?’
Ozone is a blue, slightly pungent gas, smelling of bleach. It is a form of oxygen, but
a molecule of ozone has 3 atoms of oxygen joined together instead of the usual 2 in
the oxygen molecules we breathe. This small difference is important, because
ozone is poisonous. Ozone can be good for us or bad for us, depending on where in
the atmosphere it is found. Figure 1 shows the lower parts of the atmosphere.
Figure 1. The lower atmosphere
Scientists have divided the atmosphere into different layers or zones. The lowest is
called the troposphere. This is the part of the atmosphere we live in. Above this is
the stratosphere, and this is where the ozone layer occurs. Ozone here is good for
us, because it stops harmful ultraviolet rays from reaching Earth. Ozone in the
troposphere is bad for our health and it can also damage crops and attack a wide
range of materials. The conference you are attending as part of this activity will
provide information about both tropospheric and stratospheric ozone and the
problems our modern way of life are creating with respect to ozone. You will learn
about the effects on health, crops and materials of ground-level ozone. You will also
learn about how the widespread use of certain chemicals us destroying the ozone
layer and so exposing us to the dangers of ultraviolet radiation.
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Ozone Conference
tropospheric ozone - paper 1
The formation of ozone in the troposphere
Introduction
The focus of international attention on ozone has been the problem of the ozone
layer in the stratosphere by various chemicals. However, there is another problem
with ozone that is equally important. This is to do with the level ground-level ozone,
which is as important as the ozone layer depletion.
Photochemical reactions
A number of pollutants in the atmosphere can cause the formation of ozone under
the action of sunlight. The most important of these are the oxides of nitrogen which
are often given the general name of NOx gases. These gases are formed when high
temperatures inside our car engines and furnaces caused nitrogen and oxygen in the
air to react. These NOx gases are able to react to form ozone under the action of
sunlight. Such reactions are called photochemical reactions, and nitrogen dioxide
(NO2) is especially good at doing this.
Figure 1 Photochemical reactions which produce ozone
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Major causes of NOx emissions and how they are being reduced across Europe
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European Environment Agency (EEA) reports that emissions of nitrogen oxides
(NOX) decreased by 42% between 1990 and 2010. In 2010, the most significant
sources of NOX emissions were the 'Road transport' (41%), 'Energy production
and distribution' (22%) and the 'Commercial, institutional and households' and
'Energy use in industry' (both 13%) sectors
The largest reduction of emissions since 1990 has occurred in the road transport
sector. These reductions have been achieved despite the general increase in
activity within this sector since the early 1990s and have primarily been achieved
as a result of fitting three-way catalysts to petrol fuelled vehicles. However,
ambient urban concentrations of NO2 in EU-27 countries in recent years have
not fallen by as much as reported emissions. From 2001 to 2010, NO2 annual
mean concentrations at urban background sites fell by just 10.6% on average
during which time the reported NOX emissions for the EU-27 (countries)
decreased by 24.9%. The difference between trends in NOX emissions and
ambient NO2 concentration is due in part to increased use of diesel vehicles. It is
also due to the increased proportion of NOX emitted directly as NO2 from the
exhaust of more modern diesel vehicles which use catalyst systems for
controlling emissions of other pollutants. As a result of this difference, a number
of member states' NOX emissions could be significantly higher than currently
calculated.
In the electricity/energy production sector reductions have also occurred as a
result of measures such as the introduction of combustion modification
technologies (such as use of low NOX burners), implementation of flue-gas
abatement techniques (e.g. NOX scrubbers and selective catalytic and noncatalytic reduction techniques, and fuel-switching from coal to gas.
The National Emission Ceilings Directive (NECD) specifies NOX emission
ceilings for Member States that must have been met by 2010. In general, the
newer EU Member States have made substantially better progress towards
meeting their respective NOX ceilings than the older Member States of the EU15. Eleven of the twelve post-2004 Member States had reduced their 2010
emissions beyond what is required, with the remaining one reporting
NOX emissions just 2% above the target. In contrast, only four of the EU-15
Member States reported emissions for 2010 within their respective national
ceilings. Of the three non-EU countries having emission ceilings set under the
Gothenburg protocol* (Liechtenstein, Norway and Switzerland), only Switzerland
reported 2010 emissions below the level of their 2010 ceiling.
Environmental context: NOX contributes to acid deposition and eutrophication of
soil and water. The subsequent impacts of acid deposition can be significant,
including adverse effects on aquatic ecosystems in rivers and lakes and damage
to forests, crops and other vegetation. Eutrophication can lead to severe
reductions in water quality with subsequent impacts including decreased
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biodiversity, changes in species composition and dominance, and toxicity
effects. NO2 is associated with adverse effects on human health, as at high
concentrations it can cause inflammation of the airways and reduced lung
function, increasing susceptibility to respiratory infection. It also contributes to
the formation of secondary particulate aerosols and tropospheric ozone in the
atmosphere, both of which are important air pollutants due to their adverse
impacts on human health and other climate effects.
*The Gothenburg Protocol was signed in Gothenburg, Sweden, on 30 November
1999 and entered into force on 17 May 2005.
The protocol is part of the Convention on Long-Range Transboundary Air Pollution
which is itself an international agreement to protect human health and the
environment from air pollution by control and reduction of, local and long-range, air
pollution. The agreement covers Europe, North America and countries of Eastern
Europe, Caucus and Central Asia as it is widely recognised that air pollutants can be
carried long distances, and cross-boundaries, by winds.
The protocol is a multi-pollutant protocol designed to reduce acidification,
eutrophication and ground-level ozone by setting emissions ceilings for sulphur
dioxide, nitrogen oxides, volatile organic compounds and ammonia which were to be
met by 2010.
Revisions are now underway to strengthen the Gothenburg Protocol and create new
targets for 2020. Negotiating sessions are typically held twice a year at the United
Nations office in Geneva.
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Ozone Conference
tropospheric ozone - paper 2
Monitoring Ozone across Europe
A network of ozone monitoring stations can be found across Europe to provide
detailed information about the concentrations of ozone and the changes in these
concentrations on a daily and seasonal basis.
The information provided by these stations has enabled scientists to estimate the
exposure of natural vegetation and to some extent, the human population to ozone in
different countries.
The air quality is described in the following terms:
Air quality
Hourly average ozone concentration (ppb)
Very good
0-49
Good
50-89
Poor
90-179
Very poor
above 180
(ppb = parts per billion)
These are concentrations of ozone above the natural background level. Ozone is
present all the time in low concentrations. This is the background level. Air quality
information is useful, for example, to asthma sufferers, since high ozone levels can
bring on attacks.
Sunlight is needed for NOx gases and organic solvents to react to air to make ozone,
and so the ozone level always rises in the summer months, as can be seen in Figure
1.
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Figure 1 Maximum hourly mean ozone concentrations recorded each month
Ozone levels also vary during the day. Figure 2 shows the variation at one
monitoring station.
Figure 2 The variations in ozone levels at Harwell monitoring station
Since it can be carried along by air currents, some ozone in the atmosphere can
come from elsewhere in the world. Thus it is evident that any measure to curb
pollutants that cause ozone to form must be enforced internationally, and not just in
one or two countries, if they are to be effective
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The European Environment Agency website has data and maps that show regular
monitoring across Europe. For the most up to date information please go to
http://www.eea.europa.eu/themes/air/air-quality
Also useful is a report called ‘Air pollution by ozone across Europe during summer
2012’. In total, 2,107 oz0one monitoring sites reported data for this report. Of which
2,040 were located in EU member states.
The report can be found at
www.eea.europa.eu/publications/air-pollution-by-ozone-across-EU-2012
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Ozone Conference
tropospheric ozone - paper 3
The effects of ozone on humans, plants and animals
Effects on humans
It has been known for a long time that exposure to high concentrations of ozone can
produce significant damage to the lungs. In recent years more attention has been
given to the effects of low levels of ozone, similar to those found outdoors during
summer weather. Research has shown that exposure to the levels of ozone
experienced during summertime, or during photochemical smog can cause
inflammation of the airways inside the lungs and damage the lining of the lungs. The
inflammation of the airways causes some resistance to airflow and reduction of lung
volume. It is likely that such damage will be fully repaired if the 'photochemical
episode' is short. In places such as Mexico City, Athens, Beijing and Los Angeles,
where smogs are much more frequent and ozone concentrations higher, lung
damage could be permanent. The effect of any given concentration of ozone is
considerably increased by exercise, which increases the volume of air inhaled. So
people should not take vigorous exercise when ozone levels are high.
Figure 1 The effects of ozone on Forced Expiratory Volume (FEV)
Figure 1 above shows the results of an experiment in which people were exposed to
different concentrations of ozone for 6 hours while exercising. They were required to
expel as much air from their lungs as possible in one go blowing into a bag - before
and after exposure to ozone. The amount of air expelled is called the Forced
Expiratory Volume (FEV). The reduction in the FEV after exposure shows how much
the capacity of the lungs has decreased.
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These changes in lung capacity could be a real problem for people with asthma.
There are indications that the amount of people suffering from asthma, and the
severity of their asthma, has increased over recent decades. The amount of traffic
has increased rapidly at the same time, producing increased vehicle emissions,
which leads to an increase in ozone levels.
There is evidence to suggest that ozone can increase the sensitivity of hay fever
suffered to pollen. A study showed that symptoms of hay fever (sneezing, sore
eyes, etc) were more severe when ozone levels were above 40 ppb (parts per
billion).
The World Health Organisation and European Union have drawn up guidelines on
ozone levels. These include providing information to the public if ozone rises above
90 ppb, and giving health advice if it goes above 180 ppb. In Los Angeles there are
set courses of action if ozone gets above three different levels:
1. above 200 ppb
2. above 300 ppb
3. above 500 ppb
At level 1 schools and colleges restrict the outdoor activities of students, and at level
3 the general public, schools, commercial, industrial and government activities
operate as though the day is a major national holiday.
Effects on vegetation
Controlled experiments have shown that there is a clear reduction in the yield of
some crops when ozone levels are only slightly higher than normal, i.e. 20-3- ppb.
These crops include wheat, barley, spinach, peas, beans and clover. It is estimated
that in the United States 4 billion dollars-worth of damage is done to crops by ozone
each year. Trees can be damaged by ozone. Research on young trees has shown
that levels of ozone can affect growth of certain types, especially conifers. Ozone
can also make trees less tolerant of the cold or of drought.
Effects on materials
Ozone is very reactive and its effect on polymers is well known. Cracks can
develop, for example, in rubber when a little stress is applied in the presence of very
small amounts of ozone. This can result is an economic loss for a country. Ozone
also attacks cellulose in textiles, reducing their strength as well as fading fabric.
Ozone also damages paints.
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Ozone Conference
Introduction to the 2nd session
How the ozone layer cuts down on the amount of ultraviolet radiation
reaching the surface of the Earth
Oxygen normally exists as molecules of 2 atoms, 02. This is sometimes called
dioxygen. Ozone is another form of oxygen, but with molecules of 3 atoms, O3.
The free oxygen that is released will quickly combine with an O2 molecule to re-form
ozone. In this way ozone is continually being made and destroyed, and all the time
ultraviolet radiation is being used up. This cuts down drastically the amount of UV
that reaches the earth's surface. There are about 5 billion tonnes of ozone in the
stratosphere, which may seem like a vast quantity, but if all the ozone could be
brought down to sea level and spread evenly over the Earth's surface it would be
squeezed into a layer just 3mm thick!
Ozone can also be formed by passing an electrical spark through air. So, some
ozone is made every time lightening strikes during a thunderstorm. This and some
of the ozone formed in the stratosphere reaching the Earth's surface means that
there is a small amount of ozone in the air we breathe all the time. This 'background'
ozone is present in concentrations of 20-30 ppb by volume.
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Ozone Conference
stratospheric ozone - paper A
Monitoring ozone depletion
"The hole in the ozone layer above the Antarctic was this year the second smallest is
has been in 20 years but it still covered an area roughly the size of North America.
The average size of the Earth's protective shield was 6.9 million square miles (17.9
million square kilometres), according to satellite measurement by the National
Oceanic and Atmospheric Administration (NOAA) and the US Space Agency NASA."
(Mail Online, 2th October, 2012)
Ozone is a colourless gas. Chemically, ozone is very reactive; it reacts readily with a
great many other substances. Near Earth's surface, those reactions cause rubber to
crack, hurt plant life and damage people's lung tissue. But ozone also absorbs
harmful components of sunlight, known as ultraviolet B or UB-B. High above the
surface, above even the weather systems, a layer of ozone gas absorbs UV-V,
protecting living thins below.
Concern that stratospheric ozone could be destroyed by some commonly-used
chemical was raised in the mid 1970s, but it was not until 1985 that evidence of
ozone loss was published in the scientific journal Nature. In that year scientists from
the British Antarctic Survey reported the results of work they had done the previous
year at Halley Bay in the Antarctic. They had measured ozone levels using
instruments sent up into the stratosphere on board weather balloons. These
instruments showed that the ozone concentration had fallen below half the levels
previously measured.
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The graphs below show the progress of the ozone hole in 2012. The grey shading
indicates the highest and lowest values measured since 1979.
Maximum value observed in 2012
Minimum value observed in 2012
Every year for the past few decades, during the Southern hemisphere spring,
chemical reactions involving chlorine and bromine cause ozone in the southern pole
region to be destroyed rapidly and severely. This depleted region is the ozone hole.
The area of the ozone hole is determined from a map of 'total column ozone'. It is
calculated from the area of the Earth that is enclosed with a constant value of 220
Dobson unitsi. The value of 220 Dobson Units is chosen since total ozone values of
less than 220 Dobson Units were not found in the historic observations over
Antarctica prior to 1979. Also, from direct measurements over Antarctica, a column
ozone level of less than 220 Dobson Units is a result of the ozone loss from chlorine
and bromine compounds.
i
The Dobson Unit (DU) is the measure for total ozone. If you were to take all the ozone in a column
of air stretching from the surface of the Earth to space, and bring all that ozone to standard
temperature (0°C) and pressure (1013.25 millibars, or 1 atmosphere or atm), the column would be
about 0.3cm thick. Thus, the total ozone would be 0.3 at.-cm. To make the units easier to work with,
the Dobson Unit is defined to be 0.001 atm-cm. This makes the 0.3 atm-cm 300DU
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For day by day changes in the ozone hole go to http://ozonewatch.gsfc.nasa.gov/
Thinning of the ozone layer has several consequences. There is strong evidence to
suggest that reduced levels of ozone in the stratosphere tends to cool the climate.
We haven't noticed this because carbon dioxide and other gases have produced the
Green house effect, which causes the climate to warm up. Calculations have
indicated that ozone later depletion has offset global warming by at least 30% for the
period since 1979:
Ozone depletion
Stratosphere
Cools the stratosphere
CFCs and NOx
Reduce [O3]
Less ozone means more UV
radiation = more skin cancer
Montreal protocol meeting set up
multinational agreement to phase
out CFCs
Versus
Global warming
Troposphere
Warms the troposphere
H20,CO2, CH4, etc
Traps terrestrial thermal infrared
Less infrared out means more heat
in the troposphere
Kyoto protocol meeting set up
multinational agreement to reduce
use of fossil fuels
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Ozone Conference
stratospheric ozone - paper B
The causes of ozone layer depletion
In 1974 Dr F. Sherwood Rowland and Dr Mario Molina of the University of California
published a paper which showed that a common family of chemicals called
chlorofluorocarbons, or CFCs, could cause ozone depletion. These CFCs had been
used since World War 2 in ever increasing amounts in a wide variety of applications.
One of these was as a propellant in aerosols. Propellants are added to, say,
deodorant to 'push' it out of the can when the button is depressed. CFCs were
chosen for this task because they do not react chemically with almost anything they
touch and they are not flammable. Because they are chemically inert they were
thought to be safe.
CFCs were also used to make soft foam for furniture and hard expanded polymers
such as Styrofoam. Styrofoam was used extensively as packing material,
disposable cups and fast food containers. One particular CFC, known as CFC-12 or
Freon, was widely used a refrigerator coolant, and others were used to remove
grease from computer chips and dry cleaning solvents. The work published by
Rowland and Molina caused an initial shock, not least because the manufacture of
CFCs was a multi-million dollar industry, but little or no action was taken because of
lack of evidence that the ozone layer was being destroyed. The findings of the
British Antarctic Survey in 1984 altered all that.
The problem with CFCs is the very chemical inertness that caused them to be used
in aerosols in the first place. Once expelled into the air the CFC molecules can
linger in the lower atmosphere for years before they reach the ozone layer. Once
there, they will eventually be broken down under the action of ultraviolet radiation.
As their name suggests chlorofluorocarbon molecules are made up of differing
proportions of chlorine, fluorine and carbon atoms. To illustrate what happens look
at a CFC molecule with 1 carbon atom, 3 chlorine atoms and a fluorine atom:
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Figure 1 CFCs and ozone depletion (part 1)
Ozone is constantly being broken up and re-formed by ultraviolet radiation in the
ozone layer.
Figure 2 CFCs and ozone depletion (part 2)
The free chlorine can go on to break up another ozone molecule. In fact it can carry
on doing this for perhaps a hundred years before it leaves the stratosphere, breaking
up around one hundred thousand molecules of ozone in the meantime.
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Other chemicals can also do this. They include carbon tetrachloride, an industrial
solvent; 1.1.1.trichloroethane, also a solvent used in adhesives; methyl bromide, a
powerful fumigant used to kill pests in soil, flour mills and cereal stockpiles; and
halons. Halons are another family of carbon-based chemicals, but these contain
bromine, which is a much more powerful ozone depletion agent. It has been
suggested that a quarter of the chlorine in the stratosphere could have been
released by wood-rotting fungi. Major volcanic eruptions can have a noticeable
effect on ozone depletion and there is evidence that sunspot activity could also play
a major role in the development of the ozone layer hole in the Antarctic. Scientists at
NASA have shown that the ozone concentration in the stratosphere is at its lowest
when sunspot activity is at a maximum. It is possible that the increase in particles
streaming out from the Sun in the solar wind has some effect on the formation of
ozone. However, the majority of scientists believe that CFCs, halons and other
chemicals are the main culprits in destroying ozone in the ozone layer.
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Ozone Conference
stratospheric ozone - paper C
The consequences of ozone layer depletion
When the ozone layer was formed millions of years ago, life was able to evolve on
land for the first time. This is because the layer reduced the amount of ultraviolet
radiation form the Sun that reached the ground. Ultraviolet radiation has a range of
wavelengths from 4nm to 400nm (nm = nanometre, one billionth of a metre),
between x-rays and visible light in the electromagnetic spectrum. Ultraviolet
radiation is responsible for the formation of vitamin D and it gives us a suntan. It is
very effective at killing bacteria and so UV lamps are sometimes used in food
storage rooms for this purpose. UV can also be very harmful to humans and
animals, especially in the 290 to 320nm range. This is the waveband known as UVB. It can cause skin cancers and cataracts. It can also damage DNA, causing
mutations to occur, and it can suppress the immune system, impairing the ability of
our bodied to fight off infectious diseases. UV-B can penetrate the ocean to depths
of up to 20 metres, where it can kill plankton (the base of the food chain in the sea)
and harm the larvae of fish, shrimp and crab.
Tests on some 300 plants have shown that two thirds are affected by ultraviolet
radiation. Among those particularly vulnerable are peas, melons, mustard and
cabbage. UV-B is also known to break down polymers used in buildings, paints,
packaging and many other products.
The ozone layer drastically reduces the amount of UV-B that reaches us, and
prevents any ultraviolet radiation with wavelengths below 290 nm getting to ground
level. So, any damage to this layer could have devastating consequences to the
whole world. CFCs and halons are widely blamed for causing ozone layer depletion.
These chemicals take years to get into the stratosphere and then stay around
destroying ozone for decades. So, although the use of ozone depleting chemicals
continues to decline, the chemicals that were discharged into the atmosphere earlier
may still be damaging the ozone layer.
Action on ozone depletion
On September 16, 1987 representatives met in Montreal, Canada, to discuss the
problem of ozone layer depletion. At the end of the conference the delegates signed
a document called The Montreal Protocol on Substances that deplete the ozone
layer, which was an action plan to control the use of CFCs and other chemicals.
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The idea was to freeze the level of CFC and halon production and then begin to cut
down use of CFCs, halons, etc.
As of December 29, 2010 all countries in the United Nations and the European
Opinion have ratified the original Montreal protocol.
While this protocol regulates ozone-depleting substances, scientists continue to keep
a close eye on the evolving state of the ozone in the atmosphere.
Yes, an ozone hole above Antarctica still forms each year - in 2006 it reached its
largest size ever, covering more than 11 million square miles. The ozone layer in
2012 was somewhat smaller than in the past because of the usual variations in the
Antarctic weather conditions. In the long term, worldwide adherence to the Montreal
Protocol and its amendments has scientists expecting that the ozone layer will once
again reach full strength - but they don't expect a return to 1980 global levels until
2050. The ozone hole itself could be completely eliminated by 2065.
While the Montreal Protocol may have averted disaster, the ozone layer remains in
flux, and will stay in the sights of atmosphere-observing satellites for a long time. the
The atmosphere does not have a straight line to recovery. The same chemistry that
creates the Antarctic ozone hole also takes place in the Arctic. The Arctic
stratosphere is not as cold and isolated as the Antarctic, so ozone depletion does not
usually reach the very low levels seen in the ozone hole. In the winter of 2011,
ozone depletion in the Arctic was very large because of colder than usual winter.
Colder temperatures lead to increased presence of polar stratospheric clouds; ice
crystals in these clouds speeds up chemical reactions that break down ozone.
Matt DeLand, chief scientist for Science Systems and Applications, Inc., said satellite
monitoring of the ozone layer has become increasingly important.
"We are seeing that while the overall ozone layer is getting better, we still see
changes in the arctic." DeLand said, "We shouldn't relax." While CFCs have been
regulated, greenhouse gases continue to increase, and these gases may have
unrecognised effects on our ozone layer.