The Ozone Depletion

Course: LLBSubject : Environment Laws

Unit: 3

Course: LLBSubject : Environment Laws

Unit: 3

Ozone Depletion

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

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 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 + ClOChlorine 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-B reach our earth.

Health

• Sunburn, eye diseases (cataract), skin cancer.

• Reduce our immune system other diseases

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

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)

http://archive.greenpeace.org/~ozone/gallery/sshow/sshow.html

Thank You