Plan ► What is ozone? ► Where is it found? ► What is its origin? ► Importance ► Ozone depletion ► Impacts ► Solutions: protecting the ozone layer

Ozone (O 3 ) ► A triatomic molecule, consisting of 3 oxygen atoms ► Pale blue poisonous gas ► Sharp, irritating odour ► Low T  forms a liquid ( C) and a solid ( C)

Tropospheric ozone ► In the ground layer of the troposphere ► 10% of ozone in earth’s atmosphere ► The two major sources of natural ground-level ozone:  hydrocarbons, which are released by plants and soil 2) small amounts of stratospheric ozone, which occasionally migrate down to the earth's surface.  No threat to the health of humans or the environment.

But… ► Ozone is also a byproduct of certain human activities (automobiles, fossil fuel power plants, certain industries, photocopying...)  becomes a problem at ground level ► 'bad' ozone ► Since 1900 the amount of ozone near the earth's surface has more than doubled.

-Pollutant -Constituent of smog

Impacts ► Greenhouse gas  contributes to global warming ► Pollution in the troposphere ► Irritating, reactive molecules  damage forests and crops;  destroy nylon, rubber, and other materials;  injure or destroys living tissue.

Ozone layer ► a layer in Earth's atmosphere which contains relatively high concentrations of ozone (O 3 )  much higher than the concentrations in the lower atmosphere but still small compared to the main components of the atmosphere  If the ozone layer were brought down to the Earth's surface, air pressure and temperature conditions would compress the ozone into a layer 2 to 5 mm thick! ► Over 90% of ozone in earth's atmosphere

► Absorbs 97-99% of the sun's ultraviolet light ► Located in the lower part of the stratosphere ► From 15km to 35km above Earth's surface

Origin of Ozone ► Ozone-Oxygen Cycle - a continuing process ► Photochemical mechanisms ► Researched by the British physicist Sidney Chapman Sidney Chapman

Importance ► Like a good pair of sunglasses, the ozone layer acts like a natural filter, blocking out most of the sun's harmful UV (ultraviolet) rays. ► Without the ozone layer, more people would get sunburns, skin cancer and cataracts. ► Plants and animals would also be affected (e.g. excess UV radiation damages the plants' ability to carry out photosynthesis). (e.g. excess UV radiation damages the plants' ability to carry out photosynthesis). ► Our planet's own protective sunscreen.

Ozone layer Depletion ► In recent years the thickness of this layer has been decreasing, leading in extreme cases to holes in the layer, especially over the poles ► The first ‘surprise’ – 1985 when researches discovered that 50% of the ozone over Antarctica was being destroyed in spring-summer when there was much sunlight

Causes of Ozone depletion ► “Although natural phenomena can cause temporary ozone loss, chlorine and bromine released from man-made compounds such as CFCs are now accepted as the main cause of this depletion” Drs. M. Molina and S. Rowland in 1974  CFCs discovered in 1930s  Cheap to make  became popular as  coolants in air conditioners  Coolants in refrigerators  Propellants in aerosol spray cans

Impacts of Ozone depletion ► Ecological effects ► Impact on the oceans ► Plankton- phytoplankton as well as = production of oxygen ► Zooplankton are highly sensitive to UV  Original food source for all other living organisms in the oceans.

 Causes different types of skin cancer  Impact on land plants  Increased effects of air pollution  Damage to materials

Solutions ► International action The Vienna Convention, 1985, 20 nations ► Intentions to reduce the use of CFCs. ► Before clear evidence ► 1985 – the discovery of the Antarctic hole, enhanced scientific research

 The Montreal Protocol on Substances that Deplete the Ozone Layer – 1987  Since 1987 over 180 nations have ratified a landmark environmental treaty.  The Protocol’s chief aim is to reduce and eventually eliminate the production and use of man-made ozone depleting substances, or ODS.  By agreeing to the terms of the Montreal Protocol, the nations committed to take actions to protect the ozone layer, hoping in the long- term to reverse the damage that had been done by the use of ozone depleting substances.

Summary of Montreal Protocol Control Measures Ozone Depleting Substances Developed Countries Developing Countries Chlorofluorocarbons (CFCs) Phased out end of 1995 a Total phase out by 2010 Halons Phased out end of 1993 Total phase out by 2010 Carbon tetrachloride Phased out end of 1995 a Total phase out by 2010 Methyl chloroform Phased out end of 1995 a Total phase out by 2015 Hydrochlorofluorocarbons (HCFCs) Freeze from beginning of 1996 b 35% reduction by % reduction by 2010 Freeze in % reduction by 2015 at 2015 base level Total phase out by 2020 c Total phase out by 2040 Hydrobromofluorocarbons (HBFCs) Phased out end of 1995 Methyl bromide Freeze in 1995 at 1991 base level d Freeze in 2002 at average 25% reduction by base level 50% reduction by % reduction by 2005 e 70% reduction by 2000 Total phase out by 2015 Total phase out by 2005

► Use non-ozone depleting alternative refrigerants  The major substitutes  Hydrochlorofluorocarbons (HCFCs)  Hydrofluorocarbons (HFCs) ► Recycle refrigerants ► Raise awareness

► Even given immediate action, it will take years for the ozone layer to return to 1985 levels. ► It will take another years for full recovery to pre-1950 levels.