2.1 Stratospheric ozone depletion

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Priority Rating: 5

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Description

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Depletion of stratospheric ozone (O₃), commonly known as 'the hole in the ozone layer', is an issue of international concern. Most ozone is found in the stratosphere (upper part of the atmosphere), more than 10 to 16 kms from the surface of the Earth (Fahey, 2003). The natural distribution of ozone around the Earth is not uniform, as seasonal winds and formation patterns contribute to lower concentrations at the equator and higher concentrations at the poles. Ozone in the stratosphere protects life on Earth as it limits penetration of ultraviolet radiation through the atmosphere, but it is considered a pollutant in the troposphere (close to the ground).

The ozone molecule is highly reactive and prone to splitting into oxygen atoms (O) and oxygen molecules (O₂) in the presence of ultraviolet radiation. Ozone can reform naturally, but it is usually a slow process. In the 1970s it was discovered that some human made chemicals could destroy ozone at a much faster rate, and by the early 1980s a hole in the ozone layer had formed above Antarctica (Fahey, 2003). Increases in concentration of ozone-depleting chemicals can change the balance of ozone production and destruction, which has resulted in a large area over Antarctica having very little or no ozone present during spring. Ozone-depleting chemicals include chlorofluorocarbons (CFCs), halons, carbon tetrachloride, methyl chloroform, hydrochlorofluorocarbons and methyl bromide. In the past, these chemicals were commonly used as refrigerants, foam blowing agents, industrial cleaning solvents, fire retarding chemicals and pest fumigants. The Montreal Protocol (which came into effect in 1989) provided a worldwide plan to phase out use of ozone-depleting substances.

Without adequate ozone protection, ultraviolet radiation reaches the Earth's surface and can increase the incidence of sunburn, skin cancers and cataracts, and can damage the immune system in humans and animals. Ultraviolet light can also disrupt plant photosynthesis and marine food chains. Some parts of WA are particularly susceptible to ultraviolet radiation due to predominantly clear atmospheric conditions and proximity to Antarctica - resulting in ambient ultraviolet radiation which is 10-15% higher than for comparable locations in the Northern Hemisphere (McKenzie et al., 1996, cited in Gies et al., 2004).

Objectives

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• To protect health, amenity and the environment by ensuring emissions of stratospheric ozone-depleting substances are reduced or eliminated.

Condition

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Indicator A3: Trends in stratospheric ozone concentration.

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The amount of ozone in the atmosphere is measured in Dobson units (DU). The average thickness of the atmospheric ozone layer over Perth varies from month to month, but is generally between 260 and 330 DU (Figure A1.1). In Perth, the maximum ozone thickness occurs in September and October, and the minimum in February, March and April. It is too early to detect trends in ozone layer data during the months of lowest layer thickness.

This differs from the data collected in Antarctica, where the hole in the ozone layer is largest in August, September and October (National Aeronautics and Space Administration, 2006). The United Nations Environment Program's most recent assessment showed that ozone depletion in spring remains substantial in the Antarctic region. Daily local total ozone column thicknesses are 60-70% less than in the period prior to formation of the ozone hole, with minimum values of about 100 DU seen every year since the early 1990s (United Nations Environment Programme, 2006).

Figure A1.1: Average decadal seasonal variation in ozone layer thickness, measured at Perth Airport, 1970s-2000s.

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Data source: Bureau of Meteorology - Ozone layer thickness at Perth airport [ver. 2006].

Data from southern parts of Australia (including Perth) and New Zealand shows a decline of about 4% in summer ozone concentration per decade between the late 1970s and 2000 (Manins, 2001).

Indicator A4: Size of the 'hole in the ozone layer' over Antarctica.

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There is recent evidence that the 'hole in the ozone layer' over Antarctica in 2006 was the largest on record (National Aeronautics and Space Administration, 2006). From 21-30 September 2006, the average area of the hole was 27.4 million km² - the largest average area ever observed (Figure A1.2). The largest daily average ozone hole occurred during the same period, equalling a day in 2000 where the hole reached 29.5 million km². However, cold weather conditions are likely to have also influenced the size of the ozone hole, as well as the action of ozone-depleting substances (National Aeronautics and Space Administration, 2006).

Figure A1.2: Image of the hole in the ozone layer on September 24 2006, equal record for single-day largest hole size.

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Data source: National Aeronautics and Space Administration (2006). Note: purple colours indicate very little ozone cover (i.e. the area of the 'hole') while blue, yellow and green indicate progressively thicker ozone layers.

While the largest hole in the ozone layer was seen in 2006, the average size of the ozone hole has been generally increasing over time (Figure A1.3).

Figure A1.3: Average size of the 'hole in the ozone layer' over time, 1979 to 2006.

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Data source: National Aeronautics and Space Administration - minimum, maximum and average areas of hole in the ozone layer [ver.2007].  Note: All data was collected by the Earth Probe Total Ozone Monitoring System (EP TOMS) except 1993 and 1994 (Meteor 3 TOMS) and 2005 and 2006 (OMI). Data from EP TOMS was unreliable between 2002 and 2004, and corrections have been made to these data.

Indicator A5: Trends in ultraviolet radiation for Western Australia.

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Analysis of satellite data sets from 1979 to 1992 shows that trends for ultraviolet radiation, ozone and cloud cover were not uniform over Australia (Udelhofen et al., 1999). During this period ultraviolet radiation levels showed a 4% increase over tropical Australia, increased marginally over the mid latitude areas and either decreased or remained constant over the southern portions of Australia. These patterns of ultraviolet radiation were in part a result of complex interactions between cloud cover changes and ozone depletion, but were due principally to cloud cover variations. Cloud cover over the tropics decreased by approximately 8% from 1979 to 1992, thus leading to an increase in ultraviolet radiation. In contrast, cloud increased over the southern regions by 4% and resulted in a slight decrease in ultraviolet radiation.

It should be noted that the data for 1979 to 1992 is the only data on ultraviolet radiation levels to have been analysed so far for Australia. In this period, programs to reduce use of ozone-depleting substances had not yet begun. A follow-up study covering the period from 1992 to present is planned to commence in summer of 2007-08, through a collaboration of the Australian Radiation Protection and Nuclear Safety Agency and the Bureau of Meteorology. It is likely there will have been further increases in ultraviolet radiation reaching Earth's surface since 1992 (P Gies, Australian Radiation Protection and Nuclear Safety Agency, pers. comm.).

Pressures

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Ozone-depleting chemicals are responsible for causing the hole in the ozone layer. These chemicals include chlorofluorocarbons (CFCs), halons, carbon tetrachloride, methyl chloroform, hydrochlorofluorocarbons (HCFCs) and methyl bromide. Though the production of ozone-depleting substances was restricted by the Montreal Protocol, ozone-depleting chemicals still exist in refrigerators and air conditioners. In addition, many ozone-depleting substances have relatively long lifetimes in the atmosphere. Many developing countries have significant stores of these chemicals and lack the necessary resources and institutions for preventing illegal trade and the unauthorized production and consumption of ozone-depleting substances (United Nations Environment Programme, 2006; National Aeronautics and Space Administration, 2005). However, total phasing out of these chemicals is expected between 2010 and 2040. This has largely been achieved in WA, although several exceptions are allowed under the Australian Chlorofluorocarbon Management Strategy (Environment Australia, 2001a).

Indicator A6: The concentration of ozone-depleting substances over Australia.

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The concentrations of all ozone-depleting gases were seen to rise steadily after measurements were initiated in the late 1970s (Figures A1.4, A1.5 and A1.6). Most have begun to decline in concentration, demonstrating the benefit of a global reduction in use of ozone-depleting substances. The Montreal Protocol phased out CFC-11 (primarily used in aerosol spray cans) in developed countries. Consequently, atmospheric levels of this gas have been falling since the mid 1990s (Figure A1.4).

In comparison, CFC-12 concentrations have stabilised (Figure A1.5). This gas, used in refrigerants and air conditioners, took longer to phase out than those used in aerosols and has a longer chemical lifetime in the atmosphere. Atmospheric concentrations of methyl chloroform (Figure A1.6) show a dramatic reduction from the mid 1990s. The compound was used as an industrial solvent and in dry cleaning and has a much shorter chemical lifetime.

Figure A1.4: Monthly averaged atmospheric concentrations of chlorofluorocarbon 11 at Cape Grim Tasmania.

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Data source: CSIRO Atmospheric Research and Australian Bureau of Meteorology - Cape Grim Baseline Air Pollution Station monthly averaged atmospheric chlorofluorocarbon 11.

Figure A1.5: Monthly averaged atmospheric concentrations of chlorofluorocarbon 12 at Cape Grim Tasmania.

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Data source: CSIRO Atmospheric Research and Australian Bureau of Meteorology - Cape Grim Baseline Air Pollution Station monthly averaged atmospheric chlorofluorocarbon 12.

Figure A1.6: Monthly averaged atmospheric concentrations of methyl chloroform at Cape Grim Tasmania.

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Data source: CSIRO Atmospheric Research and Australian Bureau of Meteorology - Cape Grim Baseline Air Pollution Station monthly averaged atmospheric methyl chloroform.

Although the atmospheric concentrations of ozone-reducing chemicals are generally declining, much of the damage to the ozone layer has been done, and minimum ozone concentrations are likely to occur between 2000 and 2010. Recovery of the ozone layer to 1980 levels is likely to occur around 2050.

Current responses

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Montreal Protocol: an international commitment came into force in 1989 (and was amended in 1990 and 1992) to protect the stratospheric ozone layer. It stipulates the phasing out of production and use of ozone-depleting substances, with varying timelines depending on the chemical and the status of developing countries.

Australian Chlorofluorocarbon Management Strategy: was published by Environment Australia (2001a). It provides a framework for the responsible management and use of CFCs in Australia. The strategy recognises some continuing need for these chemicals in pharmaceutical and laboratory uses, but commits to their gradual phasing out.

Environmental Protection (Ozone Protection) Policy 2000: this WA policy aims to minimise the discharge of ozone-depleting substances into the environment, and has been extended to cover use of alternative refrigerants (where relevant). This has been done to prevent current stocks of ozone-depleting substances from being released to the atmosphere by tradespeople that are not accredited, or with inadequate training and/or equipment working on systems that contain these substances.

United Nations Environment Programme: has published several assessments of the environmental effects of ozone depletion (United Nations Environment Programme, 1998; World Meteorological Organization, 2002).

Ozone Protection and Synthetic Greenhouse Gas Management Act 1989 (and associated regulations and amendments): was implemented by the Commonwealth Government to meet its commitments under the Montreal Protocol.

CSIRO Marine and Atmospheric Research: analyses information about a wide range of greenhouse gases and ozone-depleting substances.

Ultraviolet index forecast: The Bureau of Meteorology has developed a model to predict the amount of ultraviolet exposure and the times of day at which it will occur for 45 WA locations. It is designed to help people minimise their exposure to dangerous levels of ultraviolet radiation.

Implications

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As a result of the Montreal Protocol and its amendments, the concentrations of ozone-depleting substances in the troposphere peaked around 1995 and are decreasing in both the troposphere and stratosphere. It is estimated these gases reached peak levels in the Antarctica stratosphere in 2001. However, some ozone-depleting substances have very long lifetimes in the atmosphere (more than 40 years). As a result, the ozone hole is predicted to very slowly decrease in area by about 0.1 to 0.2 percent for the next five to 10 years. This slow decrease is masked by large year-to-year variations caused by Antarctic stratosphere weather fluctuations. Scientific research predicts a slow recovery of the ozone layer by the year 2065 (World Health Organisation and United Nations Environment Program, 2006).

Increased ultraviolet radiation reaching the Earth's surface can have significant detrimental impacts on animal and plant life. The radiation damages cells, causing damage to DNA and can lead to cell death or mutation and cancers. Radiation can also cause photochemical reactions in freshwater and marine waters, forming radicals (such as peroxide and hydroxide) that can cause further biological damage. Marine ecosystems in the Southern Ocean are most at risk. Zooplankton and phytoplankton, the foundation of the marine food chain, are particularly susceptible to certain types of ultraviolet radiation and impacts have flow-on effects to fish stocks and larger organisms such as whales. On land, increased ultraviolet light can cause significant damage to native vegetation and agricultural crops, such as reduced plant height, reduction in foliage area and changes to tissue composition (Caldwell et al, 2003). Like humans, some native animals and livestock may be susceptible to skin cancers. Australia has a predominately fair-skinned population and exposure to high doses of ultraviolet radiation can lead to high rates of skin cancer due to changes to the DNA caused by ultraviolet radiation (Gies et al., 2004). Increased exposure is also likely to damage the immune system and lead to increased risk of infection. Consequently, the Australian community is learning to embrace a 'Sun Smart' culture when outdoors (i.e. wearing sunscreen and protective hats, sunglasses and clothing, etc).

Suggested responses

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2.3 Maintain existing programs to ensure that ozone-depleting substances are not released: existing responses have virtually eliminated ozone-depleting substances in WA, but ongoing vigilance is required.