Ozone depletion

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Ozone depletion

• A vital topic to everyone

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Ozone

• A gas composed of three atoms of oxygen
• bluish gas that is harmful to breathe
• great majority of the ozone is concentrated on
  the stratosphere-------which is known as ozone
  layer.
• Out of each 10 million air molecules, about 2
  million are normal oxygen, but only 3 are ozone.

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• The atomic oxygen quickly combines with further
  oxygen molecules to form ozone
• O2 hv -gt O O (1)
• O O2 -gt O3 (2)
• at ground level, ozone is a health hazard - it is
  a major constituent of photochemical smog.

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• Ozone is also destroyed by the following
  reaction
• O O3 -gt O2 O2 (4)
• The Chapman Reactions

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Uses of ozone

• Ozone absorbs a band of ultraviolet radiation
  called UVB that is particularly harmful to living
  organisms which can cause cancer skin cancer amd
  damage vegetation
• thus it prevents most UVB reaching the ground

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When did the hole first appear?

• It was first observed by ground-based
  measurements from Halley Bayon the Antarctic
  coast, during the years 1980-84

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Ozone Hole over Antarctica This model shows the
ozone hole during the summer over Antarctica.
Within the model, height represents ozone
concentration.
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The Science of Ozone depletion
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• the release of chlorofluorocarbons (CFCs) into
  the atmosphere could reduce the amount of ozone

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• Although the UV radiation splits the ozone
  molecule, ozone can reform through the following
  reactions resulting in no net loss of ozone
• O3 hv -gt O2 O (3)
• O O2 -gt O3 (2) as above

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• destruction of ozone are
• HCl ClONO2 -gt HNO3 Cl2 (1)
• ClONO2 H2O -gt HNO3 HOCl (2)
• HCl HOCl -gt H2O Cl2 (3)
• N2O5 HCl -gt HNO3 ClONO (4)
• N2O5 H2O -gt 2 HNO3 (5)

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• Remember that these reaction can only take place
  in the surface
• Molecular chlorine is easily photodissociated
  (split by sunlight)
• Cl2 hv -gt Cl Cl

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• The production of active chlorine requires
  sunlight, and sunlight drives the following
  catalytic cycles thought to be the main cycles
  involving chlorine and bromine, responsible for
  destroying the ozone

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• (I) ClO ClO M -gt Cl2O2 M
• Cl2O2 hv -gt Cl ClO2
• ClO2 M -gt Cl O2 M
• then 2 x (Cl O3) -gt 2 x (ClO O2)
• net 2 O3 -gt 3 O2

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• and
• (II) ClO BrO -gt Br Cl O2
• Cl O3 -gt ClO O2
• Br O3 -gt BrO O2

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• net 2 O3 -gt 3 O2
• the above equation is known as 'catalytic
  cycles'. A catalytic cycle is one in which a
  molecule significantly changes or enables a
  reaction cycle without being altered by the cycle
  itself.

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• The production of active chlorine requires
  sunlight, and sunlight drives the following
  catalytic cycles thought to be the main cycles
  involving chlorine and bromine, responsible for
  destroying the ozone

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What is the process of ozone depletion?
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What is ODS?

• ODS is...
• Known as ozone depleting substances
• including
• CFCs, HCFCs, halons, methyl bromide, carbon
  tetrachloride, and Methyl Chloroform

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What is CFCs?

• Chloroflurocarbon
• a compound consisting of chlorine, fluorine, and
  carbon
• very stable in the stratosphere
• broke down by strong violet light in the
  stratosphere and release chlorine atoms that
  deplete the ozone layer

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Effect of Ozone depletion

• How much do you know

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Effect

• Effects on Human and Animal Health
• Effects on Terrestrial Ecosystems
• Effects on Aquatic Ecosystems
• Effects on Air Quality
• Effects on Materials

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Human and animal

• increase in the risk of cataract and skin cancer
• increases in UV-B radiation associated with ozone
  depletion are likely to lead to
• increases in the incidence and/or severity of a
  variety of short-term and long-term health
  effects
• Effects on the immune system(may be beneficial)

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• Depressed resistance to certain tumors and
  infectious diseases
• potential impairment of vaccination responses
• increased severity of some autoimmune and
  allergic responses
• decreases in the severity of certain immunologic
  diseases/conditions such as psoriasis and nickel
  allergy. (beneficial)

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Effects on Terrestrial Ecosystems

• Damage to the terrestrial organisms including
  plants and microbes.
• increased UV-B exerts effects more often through
  altered patterns of gene activity.
• affect food quality for humans and grazing animals

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Aquatic life

• solar UV-B and UV-A have adverse effects on the
  growth, photosynthesis, protein and pigment
  content, and reproduction of phytoplankton, thus
  affecting the food web
• .

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Air quality

• Increased UV-B will increase the chemical
  activity in the lower atmosphere (the
  troposphere). Tropospheric ozone levels are
  sensitive to local concentrations of nitrogen
  oxides (NOx) and hydrocarbons.
• additional UV-B radiation reduces tropospheric
  ozone in clean environments (low NOx), and
  increases tropospheric ozone in polluted areas
  (high NOx).

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• increase the concentration of hydroxyl radicals
  (OH) and result in faster removal of pollutants.

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Materials

• Physical and mechanical properties of polymers
  are negatively affected by increased UV-B in
  sunlight. Increased UV-B reduces the useful
  lifetimes of synthetic polymer products used
  outdoors and of biopolymer materials such as
  wood, paper, wool and cotton.

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What did the world do?
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1970s

• Ban on the use of CFCs as aerosal propellant in
  several countries
• However, production of CFCs and other
  ozone-depleting substances grew rapidly after the
  other ozone-depleting substances grew rapidly
  afterward as new uses were discovered

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1980s

• Worlds nations became increasingly concerned
  that OSD would harm the ozone layer.
• In 1985, the Vienna Convention was signed.
• Expected that by 1998 , the production of the
  CFCs/ODS products would reduce by half

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1990s

• Decided to completely end production of
  halons(which is ODS) by the beginnings of 1994
• end production of CFCs in 1996

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What can we small people do about it?

• No, in fact, we play an important role to
  prevent the situation form worsening!

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At home

• Repair air conditioners
• this step prevents ozone-depleting refrigerants
  from escaping. Make certain the refrigerant is
  recovered
• If you purchase a new air conditioning system or
  heat pump, purchase one that uses
  non-ozone-depleting refrigerant. See a fact sheet
  on this topic.

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• Remove the refrigerant from refrigerators, air
  conditioners, and dehumidifiers before disposing
  of the,
• If you suspect or witness unlawful releases of
  refrigerant or other improper service practices,
  you can report to the authorities concerned.

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If you are car-owners

• Repair all leaks in the a/c system
• About 80 million cars on the road today use CFC
  refrigerants in their air-conditioning (AC)
  systems. If leaky systems were repaired, it would
  prevent the release of about 30 million pounds of
  CFCs this year.
• Ask about converting your car to a substitute
  refrigerant if the a/c system needs major repair

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bare in mind that

• Everyone have the responsibility to protect our
  earth.

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Will the Ozone Layer Recover? Can We Make More
Ozone?

• ANS recovering in 50 years
• WHY?

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Thanks for watching!!!
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Reference materials

• http//www4.nationalacademies.org/beyond/beyonddis
  covery.nsf/web/ozone?OpenDocument
• www.epa.gov
• http//www.atm.ch.cam.ac.uk/tour/index.html
• http//www.nas.nasa.gov/Services/Education/Resourc
  es/TeacherWork/Ozone/Ozone.homepage.html

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• http//www.epa.gov/docs/ozone/title6/609/cons2.htm
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