Ozone Depletion
The ozone layer protects the Earth from the ultraviolet rays sent down by the sun. If the ozone layer is depleted by human action, the effects on the planet could be catastrophic.
Ozone is a bluish gas that is formed by three atoms of oxygen. The form of oxygen that humans breathe in consists of two oxygen atoms, O2. When found on the surface of the planet, ozone is considered a dangerous pollutant and is one substance responsible for producing the greenhouse effect.
Ozone is present in the stratosphere. The stratosphere reaches 30 miles above the Earth, and at the very top it contains ozone. The suns rays are absorbed by the ozone in the stratosphere and thus do not reach the Earth.
The highest regions of the stratosphere contain about 90% of all ozone.
In recent years, the ozone layer has been the subject of much discussion. And rightly so, because the ozone layer protects both plant and animal life on the planet.
The fact that the ozone layer was being depleted was discovered in the mid-1980s. The main cause of this is the release of CFCs, chlorofluorocarbons.
Antarctica was an early victim of ozone destruction. A massive hole in the ozone layer right above Antarctica now threatens not only that continent, but many others that could be the victims of Antarctica's melting icecaps. In the future, the ozone problem will have to be solved so that the protective layer can be conserved.
Causes of Ozone Depletion- Ozone depletion occurs when the natural balance between the production and destruction of stratospheric ozone is tipped in favour of destruction
-Although natural phenomena can cause temporary ozone loss, chlorine and bromine released from man-made compounds such as CFC’s are now accepted as the main cause of this depletion
-Chlorofluorocarbons (CFC’s) was likely to be the main source of ozone depletion. However, this idea was not taken seriously until the discovery of the ozone hole over Antarctica in 1985.
-CFC’s are not "washed" back to Earth by rain or destroyed in reactions with other chemicals. They simply do not break down in the lower atmosphere and they can remain in the atmosphere from 20 to 120 years or more.
-As consequences of their relative stability, CFCs are instead transported into the stratosphere where they are eventually broken down by ultraviolet rays from the sun, releasing free chlorine.
-The chlorine becomes actively involved in the process of destruction of ozone.
- Ozone is converted to oxygen, leaving the chlorine atom free to repeat the process up to 100,000 times, resulting in a reduced level of ozone
- Bromine compounds, or halons, can also destroy stratospheric ozone. Compounds containing chlorine and bromine from man-made compounds are known as industrial halocarbons.
Impacts of Ozone Depletion
Ultraviolet (UV) radiation from the Sun can cause a variety of health problems in humans, including skin cancers, eye cataracts and a reduction in the ability to fight off disease. Furthermore, UV radiation can be damaging to microscopic life in the surface oceans which forms the basis of the world’s food chain, certain varieties of vegetation including rice and soya crops, and polymers used in paints, clothing and other materials.
A loss of ozone in the stratosphere because of mankind's pollution with ozone depleting chemicals such as CFCs will increase the amount of UV radiation that reaches the Earth's surface. As a consequence, health disorders, damage to plant and aquatic life, and degradation of materials will probably increase. Ozone depletion may even affect the global climate.
A loss of ozone in the stratosphere will increase the amount of UV radiation reaching the Earth's surface. If stratospheric ozone decreases by 10% during the spring and summer, the UV radiation dose increases by about 12%. Unlike the skin, which can adapt to UV radiation by becoming browner and thicker, the eye does not have any such defence mechanisms. On the contrary, research shows that eyes become more sensitive with increased exposure to UV radiation. Increased exposure to UV radiation from ozone depletion is expected to increase the number of people experiencing cataracts and other eye disorders. A 1% decrease in stratospheric ozone may result in 100,000 to 150,000 additional cases of blindness due to eye cataracts worldwide.
The effects of ozone depletion are not limited to humans only, as it can affect animals and plants as well. It can affect important food crops like rice by adversely affecting cyanobacteria, which helps them absorb and utilize nitrogen properly. Phytoplankton, an important component of the marine food chain, can also be affected by ozone depletion. Studies in this regard have shown that ultraviolet rays can influence the survival rates of these microscopic organisms by affecting their orientation and mobility.
Materials Damage
Ozone depletion will cause many materials to degrade faster. These materials include PVC (used in window and doorframes, pipes and gutters), nylon and polyester. They are all composed of compounds known as polymers. Synthetic polymers, naturally occurring biopolymers, as well as some other materials of commercial interest are adversely affected by UV radiation from the Sun.
Today's materials are somewhat protected from UV radiation by special additives. Therefore, any increase in UV levels as a result of ozone depletion will accelerate their breakdown, limiting their useful outdoor lifetime. UV radiation is mainly responsible for photo-damage ranging from discoloration to loss of mechanical integrity in polymers exposed to sunlight.
The use of higher levels of conventional light stabilisers in polymer-based materials is likely to be employed to minimise the effects of increased UV levels reaching the Earth's surface. However, it is not certain how resistant such light stabilisers are themselves to increased levels of UV radiation. In addition, their use will add to the cost of plastic products in target applications. With plastics rapidly displacing conventional materials in numerous applications, this is an important consideration particularly in the developing world.
It is not certain yet how other materials, including rubber, paints, wood, paper and textiles will be affected by increased UV radiation resulting from ozone depletion.
The increasing concern for the causes and effects of ozone depletion led to the adoption of the Montreal Protocol, in the year 1987, in order to reduce and control the industrial emission of chlorofluorocarbons. International agreements have succeeded to a great extent in reducing the emission of these compounds, however, more cooperation and understanding among all the countries of the world is required to mitigate the problem.
Measuring Ozone Depletion
The most common stratospheric ozone measurement unit is the Dobson Unit (DU). The Dobson Unit is named after the atmospheric ozone pioneer G.M.B. Dobson who carried out the earliest studies on ozone in the atmosphere from the 1920s to the 1970s. A Dobson Unit measures the total amount of ozone in an overhead column of the atmosphere. Dobson Units are measured by how thick the layer of ozone would be if it were compressed into one layer at 0 degrees Celsius and with a pressure of one atmosphere above it. Every 0.01 millimetre thickness of the layer is equal to one Dobson Unit.
The average amount of ozone in the stratosphere across the globe is about 300 DU (or a thickness of only 3mm at 0°C and 1 atmospheric pressure!). Highest levels of ozone are usually found in the mid to high latitudes, in Canada and Siberia (360DU). When stratospheric ozone falls below 200 DU this is considered low enough to represent the beginnings of an ozone hole. Ozone holes of course commonly form during springtime above Antarctica, and to a lesser extent the Arctic.
Atmospheric lifespan of some ozone-depleting gases
 | ||
Gas | Formula | Average lifetime in atmosphere (yrs) |
|---|---|---|
| ||
CFC11 | CFCl 3 | 65 |
| ||
CFC12 | CF 2 Cl 2 | 130 |
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CFC113 | C 2 F 3 Cl 3 | 90 |
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Halon1301 | CF 3 Br | 110 |
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nitrous oxide | N 2 O | 150 |
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methane | CH 4 | 10 |
Management responses
In December 2003, the Ozone Protection Act 1989, was amended by the Australian Parliament. The amended Act is now called the Ozone Protection and Synthetic Greenhouse Gas Management Act 1989, and extends its scope in several areas. It incorporates synthetic greenhouse gases used as replacements for ozone depleting substances into the import, export and manufacturing licence system, but without any quotas or phase-outs. It empowers the Australian Government to develop national end-use controls on the purchase, sale, handling and disposal of these gases, replacing current State and Territory requirements. The amended Act also allows the Australian Government to implement the Beijing Amendment to the Montreal Protocol, banning the import and manufacture of bromochloromethane, and banning trade in certain ODS with non-Protocol countries. Further information is available from the Ozone Protection - Australian Government.
Current management responses to ozone depletion in Tasmania have largely occurred through the State's involvement in national programs and the development of Statewide legislation.
* The Environmental Management and Pollution Control Act 1994 (EMPCA) controls the use of ozone depleting substances, and their sale and purchase are restricted to authorised persons. Records of these transactions must be reported to DPIWE on an annual basis.
* The National Pollutant Inventory (NPI) is providing useful information on the scale of emissions in Tasmania. The NPI requires reporting to DPIWE from industrial facilities that exceed certain thresholds of pollutant emission. Reporting was made mandatory in Tasmania in 2002 (under Section 43 of the EMPCA), and from July 2001 reporting against 90 substances has been required (DPIWE 2002).
* National and Tasmanian Greenhouse Gas Inventories report on greenhouse gas emissions, including some ozone depleting substances (e.g. nitrous oxide, and methane).
Limited information is available on the Tasmanian involvement in the various national programs and strategies listed below.
* The Australian Halon Management Strategy (AHMS) meets our international obligations under the Montreal Protocol to provide a framework for the responsible management of Australia's halon stocks to 2030 and the ultimate elimination of their use. Under State and Territory legislation, the continued use of halon in non-essential equipment was banned in most jurisdictions from December 1995 (see Tasmania's EMPCA) (Environment Australia 2002).
* The development and operation of the National Halon Bank (NHB) has ensured the safe recovery, storage and destruction of halon in Australia (Environment Australia 2002).
* In accordance with the requirements of the Montreal Protocol, national controls on methyl bromide and HCFCs were introduced on 1 January 1996. A licence is now required for the manufacture, import or export of these substances (Environment Australia 2002).
* A Draft National Methyl Bromide Response Strategy has been developed by the Methyl Bromide Consultative Group and coordinated by Environment Australia (Environment Australia 2002).
* The Australian Chlorofluorocarbon Management Strategy was released in 2001. This Strategy outlines Australia's efforts since ratification of the Montreal Protocol in 1989 as well as its ongoing commitment to maintaining a leading role in the phase-out and responsible management of CFCs stocks in the region, in line with its international obligations (Environment Australia 2002).
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