9. Stratospheric ozone depletion

indicator policy issue DPSIR assessment
average ozone column in March any improvements already? state
total potential chlorine and bromine concentrations in the troposphere any improvements already? state
increase in UV radiation public interest indicator: how serious is the problem? state
radiative forcing of ozone-depleting substances what is the remaining effect of ozone-depleting substances on climate change? driving force
production of ozone-depleting substances are ozone-depleting substances phased out according to the schedule? is discouraging the use of HCFCs successful? driving force
contribution to multilateral fund to assist developing countries to implement the Montreal Protocol can we ensure that developing countries meet their targets? response

The thickness of the ozone layer above Europe has decreased significantly since the beginning of the 1980s and is declining at a rate of up to 8 % per decade. The gradual fall in chlorine concentrations in the troposphere (on their way to the stratosphere) shows that international policies to control ozone-depleting substances are having success. Production and sales of ozone-depleting substances in EEA member countries have fallen significantly since 1989. However, the long life of these substances in the atmosphere means that recovery of the ozone layer may not be complete until after 2050. The remaining policy challenges for European countries are to tighten control measures, to reduce the production and use of HCFCs and methyl bromide, to manage banks of existing ozone-depleting substances, and to support developing countries in their efforts to reduce their use and subsequent emissions of ozone-depleting substances.

Stratospheric ozone protects the earth’s surface from damaging short-wave ultraviolet (UV) radiation. Ozone is produced in the upper stratosphere by short-wave sunlight, which together with chemical reactions dissociates the ozone again to create a dynamic balance between production and loss. Anthropogenic emissions of inert compounds containing chlorine and bromine affect this balance. A single chlorine or bromine atom can destroy thousands of ozone molecules before being removed from the atmosphere.

Compounds causing significant ozone depletion include chlorofluorocarbons (CFCs), carbon tetrachloride, methyl chloroform, halons, hydrochlorofluorocarbons (HCFCs), hydrobromofluorocarbons (HBFCs) and methylbromide. They are used as solvents, refrigerants, foam blowing agents, degreasing agents and aerosol propellants, fire extinguishers (halons) and as agricultural pesticides (methyl bromide). The extent to which an ozone-depleting substance affects the ozone layer (i.e. its ozone-depleting potential) depends on the compound’s chemical characteristics. Other factors that affect the ozone layer include natural emissions, large volcanic eruptions, climate change and the greenhouse gases, methane and nitrous oxide.

The dramatic depletion of stratospheric ozone in polar regions is caused by a combination of anthropogenic emissions of ozone-depleting substances, stable circulation patterns, extremely low temperatures and solar radiation. Reactions on the surface of polar stratospheric cloud particles, which form at low temperatures, start a series of chemical reactions that destroy large numbers of ozone molecules in the polar spring, i.e. March/April in the Arctic and September/October in Antarctica.

The total amount of ozone over Europe is the main indicator of the state of the ozone layer above EEA member countries. The ozone column (a measure of the thickness of the ozone layer) has decreased significantly since the beginning of the 1980s (Figure 9.1); the observed trend in March is approximately -8 % per decade. The global trend in the whole winter/spring period at northern mid-latitudes is -5.4 % per decade (WMO, 1999).

Figure 9.1: Average ozone column over Europe in March

Source: RIVM
Notes: The ozone column is the amount of ozone in a column that reaches from the ground to the top of the atmosphere. Monthly average ozone data derived from satellite instruments (Nimbus 7 TOMS, Meteor3 TOMS and GOME) averaged from 35ºN to 70ºN and from 11.2ºW to 21.2ºE. Different instruments used in different years. 1 Dobson unit = 0.01 mm ozone column thickness at standard earth surface temperature and pressure.

The thickness of the ozone layer over Europe (March averages) has decreased significantly since the beginning of the 1980s by up to 8 % per decade.

The first international agreement aimed at protecting the ozone layer was the 1985 Vienna Convention. The Montreal Protocol of 1987 (and subsequent Amendments and Adjustments) aims to eliminate the production and use of ozone-depleting substances worldwide. EU measures and policies to protect the ozone layer include Council Regulation 3093/94/EC, which is in the process of being revised and strengthened (European Commission, 1999a). Current challenges in the EU include:

  • ensuring full compliance with the Protocol by developing countries, as well as in Russia and other countries with economies in transition;
  • reducing remaining production of ozone-depleting compounds for essential uses and to supply developing countries;
  • stopping the ‘dumping’ of second-hand equipment CFC-using in developing countries;
  • taking action against CFC and halon smuggling;
  • reducing emissions of halons and CFCs from existing equipment, especially in developed countries;
  • discouraging the use of HCFCs as replacements for CFCs
  • preventing the increased use of methyl bromide in developing countries;
  • preventing the production and marketing of new ozone-depleting substances.

9.1. Total potential chlorine and bromine concentrations in the troposphere

The effect of the measures taken is noticed first in the lower part of the earth’s atmosphere: the troposphere. The relevant indicator showing this effect is expressed in terms of ‘potential chlorine or bromine concentration’ and is derived from the concentrations of individual substances (taking into account the number of halogen atoms in each compound) in the troposphere. This gives a direct indication of the potential impact of these compounds on the ozone layer.

As a result of international policies, the total potential chlorine concentration in the troposphere has fallen since 1994 (Figure 9.2). The main reason for this decline is a large decrease in the concentration of methyl chloroform. The concentration of some CFCs is decreasing, while the increase in concentration of other CFCs is levelling off. However, concentrations of HCFCs (used as an alternative to CFCs) are increasing.

The concentration of potential chlorine in the stratosphere is expected to reach its maximum level by about 2000. Contrary to earlier expectations, the total potential bromine concentration is still rising due to increased concentrations of halons.

Figure 9.2: Total potential chlorine and bromine concentrations in the troposphere

Source: RIVM; ALE/GAGE/AGAGE network; NOAAA/CMDL network
Notes: Total potential chlorine/bromine is defined as the sum of the concentrations of all chlorine/bromine species in the troposphere, multiplied by the number of chlorine/bromine atoms per molecule. The sum of the bromine compounds is multiplied by the bromine efficiency factor of 60 for total potential bromine to account for the different ozone-depleting efficiency of bromine.

Although total potential chlorine concentrations in the troposphere reached their maximum around 1994, total potential bromine concentrations in the troposphere are still increasing.

Because ozone-depleting substances have a very long lifetime in the stratosphere, detectable recovery of the ozone layer due to the Montreal Protocol is not expected before 2020. Complete recovery is not expected to occur until after 2050 (WMO, 1999). Over the polar regions, extensive ozone depletion will continue to be observed in spring in the coming decades.

Ground-based measuring stations have recorded increases in the amount of UV radiation in recent years. Modelled estimates (Figure 9.3) show the percentage increase in UV radiation at wavelengths that cause human skin to turn red. These satellite-derived UV data and ground measurements generally agree.

Increased levels of UV radiation will continue until ozone recovery is complete, but the damaging effects of UV on human health and ecosystems are likely to persist even longer. Skin cancers, for example, only appear many years after exposure to UV. However, the general increase in cases of skin cancer in Europe over the past 50 years is most likely due to changes in lifestyle leading to more exposure to the sun. The anticipated effect of an increase in UV radiation will be superimposed on this effect. Public health campaigns encouraging people to reduce their exposure to the sun may offset the adverse effects of ozone depletion (United Kingdom Stratospheric Ozone Review Group, 1999).

Figure 9.3: Increase in UV radiation in Europe, 1980-1997

Source: EEA, 1999; RIVM
Note: The map shows the increase in the yearly dose of UV radiation during the 17 year period, calculated using observed total ozone values from TOMS satellite instruments and assuming clear sky conditions.

Observations suggest that UV radiation has increased above Europe.

9.2. The interaction between climate change and ozone depletion

Some ozone-depleting substances, e.g. CFCs and HCFCs, are also potent greenhouse gases. Stratospheric ozone depletion and climate change (see Chapter 8) therefore have common sources. Ozone is also a greenhouse gas, but most of the warming effect comes from troposheric ozone.

CFCs, HCFCs and related compounds contribute about 13 % to the total radiative forcing (the net extra radiation giving rise to global warming) from all greenhouse gases (Figure 9.4).However, their emissions are not regulated under the Kyoto Protocol (see Sections 8.2 and 8.3) because they are already controlled under the Montreal Protocol. HFCs, which are increasingly used as substitutes for ozone-depleting substances, are also potent greenhouse gases. HFCs are covered by the Kyoto Protocol rather than the earlier Montreal Protocol.

The radiative forcing of ozone-depleting substances is still increasing, but less than in the 1980s. There are a number of reasons for this. The phasing-out of methyl chloroform under the Montreal Protocol is largely responsible for the decrease in total potential chlorine. However, methyl chloroform contributes less to radiative forcing than CFCs and HCFCs. In addition, the contribution from CFCs is levelling off as a direct result of the Montreal Protocol and the radiative forcing of HCFCs is increasing as their concentration in the troposphere increases.

Figure 9.4: Radiative forcing of ozone-depleting substances at a global level

Source: RIVM
Note: Radiative forcing is based on global average tropospheric concentrations (Figure 9.2) and WMO radiative forcing parameters.

The radiative forcing of ozone-depleting substances is still increasing. This is because the radiative forcing of HCFCs is increasing, while that of CFCs is levelling off.

9.3 European production of ozone-depleting substances

The production of CFCs, carbon tetrachloride, methyl chloroform and halons in Europe fell substantially between 1989 and 1997, while production of HCFCs increased (Figures 9.5 and 9.6). The sale of ozone-depleting substances shows a similar pattern. This overall decline in the production and sale of ozone-depleting substances in EEA member countries is a direct result of the Montreal Protocol and EU regulations. Halon production in the EU has been banned since 1994 and production of CFCs, carbon tetrachloride and methyl chloroform since 1995. Limited production and use of certain compounds (mainly CFCs) is still allowed for designated essential uses (e.g. metered dose inhalers for medical purposes) and for use to meet the basic needs of developing countries. Production for sale to developing countries accounts for the increase in 1997. HCFCs and methyl bromide may still be produced and sold in the EU subject to mandatory limits.

The production of ozone-depleting substances in EEA member countries was about 32 % of global production in 1989 and about 25 % in 1996. In all member countries, use of ozone-depleting substances has fallen faster than required under the Montreal Protocol.

Global production and emissions of ozone-depleting substances have also decreased significantly. However, existing equipment and products still contain large amounts of CFC and halons –generating emissions when these are released. Emissions of ozone-depleting substances can occur within a few months of production (e.g. during the manufacture of open cell foams) or after several years (e.g. from refrigerators, closed-cell foams and fire extinguishers).

Smuggling and illegal production of ozone-depleting substances is estimated at 10 % of 1995 global production. These illegal activities will delay the recovery of the ozone layer by several years.

Figure 9.5: Production of ozone-depleting substances in EEA member countries

Source: European Commission 1999b; UNEP, 1998
Notes: Production is defined as actual manufacture in the EU for dispersive uses, but excluding: imports; production for use as a raw material for the production of other chemicals; and used material recovered, recycled or reclaimed. Production data is weighted according to ozone-depleting potential (ODP).

Figure 9.6: Production of HCFCs in EEA member countries

Source: European Commission, 1999b; UNEP, 1998

Production of ozone-depleting substances in EEA member countries has decreased by almost 90 %. However, production of HCFCs — with low ozone-depleting potential but high global warming potential — is increasing.

9.4 Technology transfer to developing countries

Europe’s successes and the recovery of the ozone layer will be jeopardised unless developing countries also meet their commitments under the Montreal Protocol. These came into effect in 1999.

In 1990, a multilateral fund was established by the Parties to the Montreal Protocol to help developing countries implement the Protocol. Developed countries contribute to this fund, while developing countries can apply for financial assistance for particular projects.

EEA member countries contributed US $371.6 million to the multilateral fund between 1991 and 1998. This amount is about 45 % of total global payments to the fund (Figure 9.7). The total amount spent so far by the fund (US $936 million) is expected to result in the phasing out of the use of 122 million ODP kg (more than twice the 1997 production in EEA member countries) and the phasing-out of the production of about 42 million ODP kg of ozone-depleting substances.

Figure 9.7: Relative contribution of EEA member countries to multilateral fund to assist developing countries implement the Montreal Protocol, 1991-1998

Source: UNEP, 1999

EEA member countries have together contributed around 45 % of the total multilateral fund to help developing countries reduce their emissions of ozone-depleting substances.

Methyl bromide: supporting developing countries

Twelve years after being signed, the Montreal Protocol is viewed as a success. Methyl bromide, which has an ozone-depleting potential of 0.6 compared to CFCs, was added to the list of controlled substances in 1992. The Copenhagen Amendment requires the phasing out of methyl bromide in developed countries by 2005 and in developing countries by 2015.

Methyl bromide is still used throughout the developing world as a fumigant to control pests in soils, structures and commodities. However, alternatives for 90 % of methyl bromide applications have been found . often as part of integrated pest management, but few have yet been implemented.

GTZ, the German Agency for Technical Co-operation, is advising developing countries on possible substitutes for methyl bromide. GTZ emphasises non-chemical alternatives such as crop rotation and biocontrol. GTZ is also helping with the disposal of old stocks of methyl bromide; for example, it recently helped the Sudanese government dispose of over eight tonnes of methyl bromide.
Source: UNEP

9.5 Indicator improvement

Harmonisation of data reportingon current production and sale of ozone-depleting substances to both the European Commission and the United Nations Environment Programme (UNEP) would remove some inconsistencies from the indicators.Data on individual EU Member States is not available.

For the future, improved breakdowns for contributions by European countries to the multi-lateral fund to help developing countries implement the Montreal Protocol would be desirable.Analysis of the effectiveness of this policy instrument in helping to reduce the production and consumption of ozone-depleting substances in developing countries would also be useful.

For the future, improved indicators and analysis of the interactions between climate change and ozone depletion should be developed. Radiative forcing, which is presented here, is just one example of such an indicator. Another interesting interaction is the temperature fall in the stratosphere due to greenhouse gas emissions and its effect on the ozone layer at mid-latitudes and polar regions. However, this interaction is more difficult to assess.

9.6. References and further reading

EEA (1999). Environment in the European Union at the turn of the century. European Environment Agency, Copenhagen.

European Commission, DG Research (1997). European research in the stratosphere. EUR 169986 EN. European Commission, Brussels.

European Commission (1999a). ‘A Common Position for a revised Council Regulation on substances that deplete the ozone layer 5748/99.’ Official Journal C123/03.

European Commission (1999b). Statistical factsheet — ozone-depleting substances. European Commission, Brussels.

WMO (1999). Scientific assessment of ozone depletion: 1998. World Meteorological Organisation Global Ozone Research and Monitoring Project — Report 44. World Meteorological Organisation, Geneva.

UNEP (1998). Production and consumption of ozone-depleting substances 1986-1996. United Nations Environment Programme, Nairobi, Kenya.

UNEP (1999), UNEP/OzL.Pro/ExCom/27/48 (Annex I, Page 5). United Nations Environment Programme, Nairobi, Kenya (

United Kingdom Stratospheric Ozone Review Group (1999). Stratospheric ozone 1999. Department of the Environment, Transport and the Regions, London, UK.


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