Ozone Depletion

Vishal ShuklaVishal ShuklaIndiaIndia

Importance of the ozone layer

Near ground level (trochosphere) - pollution

Form photochemical smog and acid rain

In 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 troposphere- Temperature increases with altitude- Contains 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 wavelengths• Decrease 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 stratosphere Oxygen molecules dissociate into atomic oxygen

Atomic oxygen quickly combines with other oxygen molecules to form ozone

O2 O + O

O + O2 O3

Ozone formation [3]

Ozone (O3) A pollutant on ground level

– A component of photochemical smog

Important for our survival– Absorbs some of the potentially harmful UV radiation

which can cause skin cancer and damage to vegetation

Split and regenerate repeatedly Highest concentration in the upper atmosphere Concentration decreases at lower altitudes

Ozone formation [1]

Ozone (O3) Made up of three oxygen atoms Occurs naturally as a layer in the stratosphere The layer is thinnest around the equator and the

concentration increases towards the poles The amount of ozone above a point on the earth’s

surface is measured in Dobson units (DU)– ~ 260 DU near the Tropics– higher elsewhere

What is CFCs? [1]

Chlorofluorocarbons (CFCs) Composed of elements chlorine, fluorine, and

carbon Developed in 1930 by DuPont CFCs were welcomed by industries:

– Low toxicity– Chemical stability– Cheap

Usage:– As refrigerants– As blowing agents– For making flexible foam– As cleaning agents– As propellants

CFCs are used in aerosol sprays CFCs were used as refrigerants in the past

Present situation

Stratospheric ozone over Antarctica:– Has been depleted over the last 15 years– The ozone hole:

enlarging large enough to cover most of the North America would 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 + ClO

Chlorine monoxide then combines with another oxygen atom to form a new oxygen molecule and a chlorine atom.

ClO + O Cl + O2

The chlorine atom is free to destroy up to 100,000 ozone molecules

Causes of ozone depletion Details are not fully understood Catalyzed by halocarbons (carbon compounds

containing fluorine, chlorine, bromine and iodine)– Examples: CFCs and ClONO2

Halogen 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 ozone

Because CFCs has long life span and very stable, it continuous to attack the ozone layer and more UV reach our earth.

Impacts on human health

Skin Cancer Cataracts and Other Eye Damages Suppression of Immunity

Food supply

Reduce photosynthesis - crops affected.

Kills plankton fish

Impacts on other animals Reduces plankton population Reduces penguin population Reduces the percentage of hatching of

frog eggs

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 US

Phaseout of production of CFCs Substitutes 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 makers

US - 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 countries- because 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 work- to 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

Discussion Naturally, 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)