Ozone Depletion

Protest against ozone depletionhttp://archive.greenpeace.org/~ozone/gallery/sshow/sshow.html

Video showAnswer the questions on p. 1

Importance of the ozone layerNear ground level (trochosphere) - pollutionForm photochemical smog and acid rainIn the stratosphere (15 - 50 km) - ozone layer screen out harmful Ultra-violet radiation from the sun.

Our atmosphere [1]Troposphere: The lowest layer (about 15 km from the ground)Contains normal air composed of N2, O2, water vapour, CO2, etc.Temperature decreases with altitude

Stratosphere:Above the troposphereTemperature increases with altitudeContains a lot of ozone (ozone layer):Found in the stratosphere between 10 - 50km above the ground Protects us from the harmful effects of UV of certain wavelengthsDecrease in ozone concentration Increase in UV-B radiation reaching the earth surface

Formation of ozone layer

O2 + sunlight O + O

O + O2 O3

Ozone formation [2]Ozone (O3)Chemically forms when UV hits on stratosphereOxygen molecules dissociate into atomic oxygenAtomic oxygen quickly combines with other oxygen molecules to form ozoneO2 O + OO + O2O3

Ozone formation [3]Ozone (O3)A pollutant on ground levelA component of photochemical smogImportant for our survivalAbsorbs some of the potentially harmful UV radiation which can cause skin cancer and damage to vegetation Split and regenerate repeatedlyHighest concentration in the upper atmosphereConcentration decreases at lower altitudes

Ozone formation [1]Ozone (O3)Made up of three oxygen atomsOccurs naturally as a layer in the stratosphereThe layer is thinnest around the equator and the concentration increases towards the polesThe amount of ozone above a point on the earths surface is measured in Dobson units (DU)~ 260 DU near the Tropicshigher elsewhere

What is CFCs? [1]Chlorofluorocarbons (CFCs)Composed of elements chlorine, fluorine, and carbonDeveloped in 1930 by DuPontCFCs were welcomed by industries:Low toxicityChemical stabilityCheapUsage:As refrigerantsAs blowing agentsFor making flexible foamAs cleaning agentsAs propellants

What is CFCs? [2]CFCs are used in aerosol sprays (Sources: http://www.yahoo.com) CFCs were used as refrigerants in the past (Sources: http://www.yahoo.com )

Present situationStratospheric ozone over Antarctica:Has been depleted over the last 15 yearsThe ozone hole:enlarginglarge enough to cover most of the North Americawould take at least 50 years to restore

Destruction of ozone layerChlorine atoms from CFCs attack the ozone, taking away ozone and forming chlorine monoxide (ClO).O3 + Cl O2 + ClOChlorine monoxide then combines with another oxygen atom to form a new oxygen molecule and a chlorine atom.ClO + O Cl + O2The chlorine atom is free to destroy up to 100,000 ozone molecules

Causes of ozone depletionDetails are not fully understoodCatalyzed by halocarbons (carbon compounds containing fluorine, chlorine, bromine and iodine)Examples: CFCs and ClONO2Halogen atoms catalyze ozone layer depletion by destroying ozone molecules and forming oxygen molecules.Much more serious in Antarctica than other regions on the planet

Consequences of less ozoneBecause CFCs has long life span and very stable, it continuous to attack the ozone layer and more UV-B reach our earth.

HealthSunburn, eye diseases (cataract), skin cancer.Reduce our immune system other diseases

Impacts on human healthSkin CancerCataracts and Other Eye DamagesSuppression of Immunity

Food supplyReduce photosynthesis - crops affected.Kills plankton fish

Impacts on other animalsReduces plankton populationReduces penguin populationReduces the percentage of hatching of frog eggs

Air pollutionForming photochemical smog

Degrades building materials

What has been done? [1]Ban the use of CFCs as aerosol propellants The Vienna Convention on the Protection of the Ozone Layer in 1985 Governments committed themselves to protect the ozone layer and to co-operate with each other to improve understanding of ozone crisis. The Montreal Protocol on Substances that deplete the Ozone Layer Adopted by Governments in 1987 Aims to reduce and eventually eliminate the emissions of man-made ozone-depleting substances.International cooperation:

What has been done? [2]

SunWise School Program by EPA of the USPhaseout of production of CFCsSubstitutes for CFCs

1. How do scientists monitor the ozone level in the stratosphere? Are the measurements accurate?Monitoringa. 1970s - 67 measuring stations at ground level - uneven distribution - too short to identify statistically significant trends. - calculations contain inherent uncertainties incomplete scientific description built in the computer programme.b. 1979 - Total Ozone Mapping Spectrometer on satellites (TOMS) - global data available

2. How serious is the problem Of ozone depletion? Seriousness of ozone depletion: 1992 - average ozone concentration is 2-3% lower than before Northern parts of Europe and Canada 20% lower in 93 winter Antarctic - 50-90% lower every winter

3. Are there any proofs that CFCs cause the depletion of ozone? Chlorine monoxide which is an intermediate formed in the destruction of ozone.

4. Why was there such a great difference in terms of the attitudes of policy makers in the US and Europe towards the warning of scientists about CFCs in the 70's? Attitudes of policy makersUS - NAS and EPA support scientists warning of the problem and recommend banning wide coverage in the media increased public concern

Britain - Environmental Depths report with a cautious tone, against the need for precipitate action public debate of lower profile

5. Will the Montreal Protocol save the ozone layer?

Montreal Protocol -- came too late -- countries which had signed the Protocol had not taken any immediate and practical action. -- the chemicals already produced will continue to seep into the atmosphere and attack the ozone layer.-- Many countries refused to cut down the use of CFCs (e.g. China / India) unless they get some financial help in meeting their demand.

6. What do you think make policy makers sign the Montreal Protocol?

Public pressure because of growing public, scientific and political concern.

7. Why are there exceptions for developing countries for the Protocol?

Exceptions for developing countriesbecause they do not have the technology to switch to alternatives, refuse to sign the protocol.- to encourage them to participate in the protocol. - growing domestic needs and potential markets for CFCs.

8. Why don't developing countries agree to the standards of the Protocol? What can be done to make them cut their use of CFCs?

Financial and technological aids can help LDCs to cut CFCs use

9. What are the reactions of business to the Montreal Protocol?

Reactions of business- finding substitutes- developing new technologies- surprising results: save money & improve performance

10. Other than stopping CFC production, what other remedial work should be done? Are there any obstacles to these?

Other remedial workto develop systems for recovery & recycling the chemicals already used.

Obstacles- technical challenge, diplomatic challenge

11. What are the alternatives for CFCs? Are they expensive? Who will promote the use of these alternatives?

Alternatives for CFCs- ammonia, propane, water- cheap because abundant and not patented- scientists and business which foresee the advantage of using such alternatives (energy saving, cheap), but not chemical companies

12. Are there any relationships between the Greenhouse Effect and ozone depletion?Similarities between GHE and Ozone Depletion issue- long-term environmental impact which affect future generations, e.g. food supply- prediction of future impact involves scientific uncertainties

- global problem - difficult to impose environmental regulations- clash with economic interests or conflicts among countries- no immediate action to deal with the problem although many conference concerning about this problem.

13. Contrast the reactions of policy makers towards the issue of global warming and ozone depletion. Why do you think there's such a difference in attitudes? - Policy makers have taken action for the ozone issue before there is scientific proof (1985: Vienna Convention; proof came in 1987) but not GHE - reasons: - image of a hole in the sky, through which pour deadly cancer-causing rays exerted a powerful hold on the public imagination great pressure on policy makers to do something

- effect of ozone depletion already felt with reports of increase in cancer risk e.g. in Australia- effects of GHE do not create so much disturbance among average citizens; melting of ice, flooding, species extinction: seem not to be direct effects on individuals' well-being

DiscussionNaturally, there is a balance of ozone formation and depletion. What disturb this balance?What are the functions of the ozone layer?How to reduce emission of ozone depleting substances? Do you agree that people living in the southern hemisphere are more prone to skin cancer than those living in the northern hemisphere? Why?

Relevant websites [1]US Environmental Protection Agency (http://www.epa.gov)The Science of Ozone Depletion (http://www.epa.gov/students/ozone_depletion.htm)United States Environmental Protection Agency: Ozone Depletion Home Page (http://www.epa.gov/docs/ozone/)USA NASA (http://www.nasa.gov)NASA-Stratospheric Ozone Depletion Tutorial (http://www.nas.nasa.gov/About/Education/Ozone)Union of Concerned Scientists (http://www.ucsusa.org)Ozone Depletion (http://www.ucsusa.org/ozonedepletion/ozone.sciupdate.html)

Relevant websites [2]The National Oceanic and Atmospheric Administration (NOAA) (http://www.al.noaa.gov)WMO/UNEP Scientific Assessment of Ozone Depletion 1994 (http://www.al.noaa.gov/WWWHD/pubdocs/Assessment94.html)Hong Kong Cyber Campus (http:/www.hkcampus.net/main.phtml)Ozone depletion (http://cwc.hkcampus.net/~cwc-fkc/Ozone%20Depletion.files/frame.htm)Chemistry Summer Project Work (http://ucc.hkcampus.net/~ucc-ckt/ozone/first.htm)