Energie und Umwelt IER - Universität Stuttgart und Umwelt Prof. Dr.-Ing. Rainer Friedrich IER Reduzierung der Ozonkonzentration in der Stratosphäre ... 400.000 19 3 …

Energie und UmweltProf. Dr.-Ing. Rainer Friedrich

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Reduzierung der Ozonkonzentration in der Stratosphäre (‘Ozonloch’)


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Troposphärischer (2, 4, 6 und 8 km Höhe) und stratosphärischer (20, 22, 24 km Höhe) Ozontrend 1976-1990 am Hohenpeissenberg bei

München


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Spektrale Energieverteilung der Sonnenstrahlen1.Ausstrahlung einer Oberfläche mit 6000 K (Sonne)2.Sonnenstrahlung außerhalb der Atmosphäre (extraterrestrisch) 3.Sonnenstrahlung unterhalb der Ozonschicht 4.Sonnenstrahlung an der Erdoberfläche unter einer wasserdampffreien Atmosphäre 5.dasselbe mit durchschnittlicher Wasserdampfabsorption


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O2 + hν (λ<242 nm) 2 O2 [ O + O2 O3 ]

-----------------------------3 O2 2 O3

Ozone Production in the Stratosphere


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The role of CFC´s

Cl + O3 ClO + O2

O3 + hν O + O2

ClO + O Cl + O2---------------------

2 O3 + hν 3 O2

1) Production of chloro-radicals: CFCl3 + hν CFCl2 + Cl

2 Cl + 2 O3 2 ClO + 2 O2

ClO +ClO + M Cl2O2 + M

Cl2O2 + hν 2 Cl + O2---------------------

2 O3 + hν 3 O2

2) Destruction processes of ozone:

However, due to quenching processes using NO2, ClO is removed from the processes above:

HO + NO2 + M HNO3 + M

ClO + NO2 +M ClONO2 + M

⇒Thus the ozone concentration remains relatively high


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The ozone hole - The role of CFC´s

Cl + O3 ClO + O2

O3 + hν O + O2

ClO + O Cl + O2---------------------

2 O3 + hν 3 O2

1) Production of chloro-radicals: CFCl3 + hν CFCl2 + Cl

2 Cl + 2 O3 2 ClO + 2 O2

ClO +ClO + M Cl2O2 + M

Cl2O2 + hν 2 Cl + O2---------------------

2 O3 + hν 3 O2

2) Destruction processes of ozone:

Quenching processes:

HO + NO2 + M HNO3 + M

ClO + NO2 +M ClONO2 + M

⇒Radical reservoirs

Photolysis of the quenchingproducts

HNO3 + hν OH + NO2

ClONO2 + hν ClO + NO2


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The ‘ozone hole’ = reduction of concentration of ozone above the Antarctic in September and October

During the polar winter (no solar radiation, < - 80° C) polar stratospheric clouds (PSC) with frozen water and HNO3molecules are formed

e.g. by the following reaction that is fast on ice surfaces: ClONO2 + HCl Cl2↑ + HNO3 (ice)

-> as soon as sunlight is available (end of Sept.), photo dissociation of Cl2 starts: Cl2 + hν 2 Cl .

-> However NO2 ( reaction HNO3 + hν OH + NO2 ) is not yet formed, as HNO3 is still hold in ice -> no quenching reaction

-> ozone is destroyed.


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Chlorofluorocarbons CFCs

- Developed in 1928 by Thomas Midgley as refrigerants

- Stable, non-flammable, non-toxic chemicals- Physical properties ideal for many uses such as

aerosols, refrigeration, air-conditioning, blowing agents for foam packaging and insulation, solvents, dry-cleaning, etc.

- Rapid growth in sales from the 1940s onwards until ..


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CFC-11 CClF3CFC-12 CCl2F2CFC-113 CCl3CF3CFC-114 CCl2FCF3CFC-115 CClF2CF3

HCFC-22 CHClF2 HFC-32 CH2F2HCFC-123 CHCl2CF3 HFC-125 CHF2CF3HCFC-124 CHClF2CF3 HFC-134a CH2FCF3HCFC-141b CH3CCl2F HFC-143a CH3CF3HCFC-142b CH3CClF2 HFC-152a CH3CHF2HCFC-225ca CHCl2CF2CF3 HFC-227ea CF3CHFCF3HCFC-225cb CHClFCF2CClF2 HFC-236fa CF3CH2CF3

HFC-245fa CF3CH2CHF2HFC-245ca CHF2CF2CH2FHFC-245eb CF3CHFCH2FHFC-365mfc CF3CH2CF2CH3

Chlorofluorocarbon (CFCs)

Fluorocarbon Alternatives to CFCs


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CFC Production – total by 1972 over 5 Mio t

0

50.000

100.000

150.000

200.000

250.000

300.000

350.000

400.000

1931

1935

1939

1943

1947

1951

1955

1959

1963

1967

1971

CFC-11CFC-12


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Chlorofluorocarbons CFCs

- 1972 CMA Fluorocarbon Program Panel set up to look at „the effect (if any) of CFCs on the atmosphere“

- Atmospheric measurements found traces of CFCs in „clean air“

- 1974 Rowland and Molina hypothesis: CFCs broken down by UV in the stratosphere. Cl atoms enter into a catalytic cycle that breaks down ozone

- 1980s US aerosol ban, European production cap- First signs of Antarctic Ozone Hole - 1987 Montreal Protocol


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CFC Production to 1988

0 50.000

100.000 150.000 200.000 250.000 300.000 350.000 400.000 450.000 500.000

1931

1936

1941

1946

1951

1956

1961

1966

1971

1976

1981

1986

CFC-11CFC-12


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Fluorocarbon alternatives to CFCs

- Hydrochlorofluorocarbons (HCFCs) and Hydrofluorocarbons (HFCs) developed from the mid-1970s onwards

- Unprecedented amount of environmental testing- Less than 25% take up as alternatives to CFCs- Mostly in refrigeration, air-conditioning and foam-

blowing- Aerosol and solvent markets went almost entirely

over to non-fluorocarbon alternatives: hydrocarbons, ammonia, water, alternative technologies


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International Regulations on Fluorocarbons

- 1987 UN Montreal Protocol and later amendments

- Regulate consumption of CFCs and HCFCs- 1992 UN Framework Convention on Climate

Change (UNFCCC) adopted at Earth Summit in Rio

- 1997 Kyoto Protocol negotiated as amendment to UNFCCC – came into force in 2005

- Aims to reduce emissions of CO2 and five other greenhouse gases: CH4, N20, PFCs, SF6 and HFCs


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Montreal Protocol

- Developed countries phase out CFCs, methylchloroform, carbon tetrachloride by 1996

- Can produce CFCs up to 15% of 1986 baseline for developing countries and own essential uses

- Freeze HCFC production in 1996; phase out by2030

- Developing countries can produce and purchaseCFCs and carbon tetrachloride until 2010 and methyl chloroform until 2015

- Freeze HCFC consumption in 2015, phase out by 2040


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CFC phase out-schedule in developed countries

1987 1990 1992 1990 1994

Original Montreal Protocol

London Montreal Protocol

Copenhagen Montreal Protocol

U.S. Clean Air Act

Amendments

European Community Schedule

1990 100%1991 100% 100% 85%1992 100% 100% 80%1993 80% 80% 75% 50%1994 80% 80% 25% 25% 15%1995 80% 50% 25% 25% 0%1996 80% 50% 0% 0%1997 80% 15%1998 80% 15%1999 50% 15%2000 50% 0%


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Ozone depletion potentials


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0

50.000

100.000

150.000

200.000

250.000

300.000

350.000

400.000

450.000

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

Met

ric T

ons

(10^

3 kg

)

CFC-11

CFC-12

CFC-113

CFC-114

CFC-115

HCFC-22

HCFC-124

HCFC141bHCFC142b

HFC-134a

HFC-125

HFC-143a

Fluorocarbon production data reported to AFEAS (2005)


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Energie und Umwelt IER - Universität Stuttgart und Umwelt Prof. Dr.-Ing. Rainer Friedrich IER Reduzierung der Ozonkonzentration in der Stratosphäre ... 400.000 19 3 …