Transcript Environmental Issues

Ozone Layer
and Extinction of Species
Contents
Ozone layer depletion
 Extinction of species and loss of
biodiversity
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Ozone Layer Depletion
Source of ozone
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Consisted of 3 oxygen atoms, unlike
ordinary oxygen molecule (which has 2
atoms).
It has a bluish colour.
Dual role of Ozone
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At near ground level, ozone is an air
pollutant. Even at a low concentration
(ppm), it is irritating to respiratory
system.
It is strongly oxidizing, and is now
commonly used in sterilization of water.
Its presence in the stratosphere is vital
to life on Earth as it can absorb harmful
ultra-violet radiation (known as UVB,
wavelength 270-315nm) from sunlight.
Structure of Atmosphere
Source: NASA
Formation of Ozone in
stratosphere
O2 + (radiation < 240nm) → 2 O
O2 + O + M → O3 + M
Molecule M carries the energy of the
reaction but remain unchanged.
Destruction of Ozone (I)
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Ozone can be destroyed by a number of free
radical catalysts, the most important of which
are the hydroxyl radical (OH·), the nitric oxide
radical (NO·) and atomic chlorine (Cl·) and
bromine (Br·).
Human activity has dramatically increased the
chlorine and bromine. These elements are found
in certain stable organic compounds, especially
chlorofluorocarbons (CFCs), which may find their
way to the stratosphere without being destroyed
in the troposphere due to low reactivity. Once in
the stratosphere, the Cl and Br atoms are
liberated from the parent compounds by the
action of ultraviolet light, and can destroy ozone
molecules through a variety of catalytic cycles.
Destruction of Ozone (II)
Cl + O3 → ClO + O2
ClO + O → Cl + O2
In sum O3 + O → O2 + O2
=>Increase rate of recombination of
oxygen, leading to an overall
decrease in the amount of ozone.
Ozone hole in September
2006
“Largest hole in the record.”
~Size of North America
Source: NASA
Concentration Ozone in Antarctic
region
Consequences of Ozone
depletion
Since the ozone layer absorbs UVB
ultraviolet light from the Sun, ozone
layer depletion is expected to
increase surface UVB levels.
 Possible linked to higher incidence of
skin cancer.
 Lead to decrease of crop yield.
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Montreal Protocol
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The Montreal Protocol on Substances That
Deplete the Ozone Layer is an international
treaty designed to protect the ozone layer by
phasing out the production of a number of
substances believed to be responsible for ozone
depletion. The treaty entered into force on
January 1, 1989.
Due to its widespread adoption and
implementation it has been hailed as an example
of exceptional international cooperation
"Perhaps the single most successful international
agreement to date...".
Ozone Depleting
Substances
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Chlorofluorocarbons (CFCs) were used in
air conditioning/cooling units, as aerosol
spray propellants prior to the 1980s, and
in the cleaning processes of delicate
electronic equipment.
It is calculated that a CFC molecule takes
an average of 15 years to go from the
ground level up to the upper atmosphere,
and it can stay there for about a century,
destroying up to 100,000 ozone
molecules during that time.
Current situation
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CFCs have been replaced to some extent
by the less damaging hydro-chlorofluoro-carbons (HCFCs), although
concerns remain regarding HCFCs also. In
some applications, hydro-fluoro-carbons
(HFCs) have been used to replace CFCs.
HFCs, which contain no chlorine or
bromine, do not contribute at all to ozone
depletion although they are potent
greenhouse gases.
Recovery of Ozone Layer
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Since the adoption and strengthening of the
Montreal Protocol has led to reductions in the
emissions of CFCs, atmospheric concentrations
of the most significant compounds have been
declining. These substances are being
gradually removed from the atmosphere.
By 2015, the Antarctic ozone hole would have
reduced by only 1 million km² out of 25
Complete recovery of the Antarctic ozone layer
will not occur until the year 2050 or later.
A detectable recovery will not occur until
around 2024, with ozone levels recovering to
1980 levels by around 2068.
Extinction and Loss of
Biodiversity
“Earth’s Sixth Mass
Extinction”
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Since 1500 AD, 784 extinctions have
been documented by the International
Union for Conservation of Nature and
Natural Resources.
However, since most extinctions are likely
to go undocumented, scientists estimate
that during the last century, between
20,000 and two million species have
become extinct, but the precise total
cannot be determined more accurately
within the limits of present knowledge.
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The World Conservation Union’s IUCN
Red List contains 15,589 species
threatened with extinction in 2004.
According to a 1998 survey of 400
biologists conducted by New York's
American Museum of Natural History,
nearly 70 percent of biologists believe
that we are currently in the early stages
of a human-caused mass extinction
The same proportion of respondents
agreed with the prediction that up to 20
percent of all living species could
become extinct within 30 years (by
2028).
Cause of extinction of
species
Deforestation
 Habitat destruction, degradation or
fragmentation
 Over-exploitation / hunting
 Human population growth
 Pollution
 Introduction of exotic species
 Climate change
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Some examples of extinct
species
Dodo on a flightless bird living on
A small island in Indian Ocean. They
Are hunted to extinction in late 17th
Century by sailors and dogs brought
By them as food.
Baiji, Chinese River Dolphin
Declared functionaly extinct in 2006
Bali Tiger gone extinct in 1937
Link
Extinction of Species and
Biodiversity
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Extinction of species cause a
irreversible loss of biodiversity.
Importance of biodiversity
Possible new sources of food and
drink in unknown species
 Possible new medicine
 Possible new industrial materials
 Ecosystem provides important vital
resources such as oxygen, fresh
water and food.
 Leisure, cultural and aesthetic value
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Discussion Question
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What can we do in response of the
mass extinction of species?