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Une nouvelle menace pour la couche d’ozone ?

Bruno FRANCO

Based on Mahieu et al.: Recent Northern Hemisphere stratospheric HCl increase due to

atmospheric circulation changes, Nature, 515, 104-107, doi:10.1038/nature13857

(2)

-> The largest O3 production occurs in the tropical stratosphere

=> Production/destruction of stratospheric O3 normally in balance

Photolysis

B.Franco : Assemblée générale AGO, ULg, 4 Décembre 2014

Sources: Fahey, D.W., and M.I. Hegglin: WMO 2010

Sources: Fahey, D.W., and M.I. Hegglin: WMO 2010

(3)

Global satellite maps of total O3 in 2009

=> During polar night, O3 accumulates and the poles

act as a reservoir

Sources: Fahey, D.W., and M.I. Hegglin: WMO 2010

(4)

=> But since the 1950s…the CFCs

(5)

Chlorine Source Gases entering the stratosphere in 2008

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Organic chlorine (CCly) = ∑ CFCs + HCFCs + CCl4 + … Inorganic chlorine (Cly) = HCl + ClONO2 + (ClO + HOCl + …)

+

Cl

+ H+ + O--+ NO 2

=> at mid-latitudes

-> HCl and ClONO2 as a reservoir of UNREACTIVE chlorine

Sources: Fahey, D.W., and M.I. Hegglin: WMO 2010

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-> At the beginning of winter

(8)

-> But over high-latitudes... the PSCs

Polar Stratospheric Clouds

HCl + ClONO2 + … Cl2

During the polar nights

Low-temperature surface reactions (≈ 15 – 25 km altitude; T° < -78 °C)

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-> But over high-latitudes... the PSCs

Polar Stratospheric Clouds

HCl + ClONO2 + … Cl2

During the polar nights

Cl + ClO +

=> Production of REACTIVE chlorine

HNO3 Low-temperature surface reactions

(10)

-> Chlorine catalytic cycle

(11)

-> At the beginning of spring

(12)

CFCs

HCFCs

HFCs & PFCs

(13)

Within the framework of the Network for the Detection of Atmospheric Composition Change

(NDACC; see www.ndacc.org)

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(15)
(16)

CF4 (PFC) ≈ 50,000 yr lifetime !!! Phased out by the Montreal Protocol

Phased out by the Montreal Protocol amendments

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Cly ≈ HCl + ClONO2

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Cly ≈ HCl + ClONO2

CCly = CFCs + HCFCs + CCl4 + … 3.5 yr

(19)

-> Monitoring of HCl at Jungfraujoch Global total tropospheric chlorine HCl time series at Jungfraujoch

(20)

-> Monitoring of HCl at Jungfraujoch Global total tropospheric chlorine HCl time series at Jungfraujoch 3-D SLIMCAT chemical transport model Recent HCl upturn

(21)

-> Recent HCl upturn: hypothesis?

(22)

-> Transfer between stratospheric chlorine reservoirs?

Cly ≈ HCl + ClONO2 HCl

(23)

-> Recent HCl upturn: hypothesis?

« Rogue » emissions of HCl precursors?

- Unregulated by the Montreal Protocol

(24)

-> Monitoring of HCl at Jungfraujoch

Global total tropospheric chlorine from in situ measurement networks HCl time

series at Jungfraujoch

(25)

-> Recent HCl upturn: hypothesis?

« Rogue » emissions of HCl precursors?

- Not monitored by measurement networks

Transfer between stratospheric chlorine reservoirs?

(26)

-> Monitoring of HCl at Jungfraujoch Global total tropospheric chlorine HCl time series at Jungfraujoch 3-D SLIMCAT chemical transport model Recent HCl upturn

SLIMCAT run with constant 2000 meteorological forcing

(27)

-> Investigation of the recent HCl upturn

8 FTIR NDACC sites

3 satellite missions (GOZCARDS data) - Ny-Ålesund (79 °N) - Thule (77 °N) - Kiruna (68 °N) - Jungfraujoch (47 °N) - Tsukuba (36 °N) - Izana (28 °N) - Wollongong (34 °S) - Lauder (45 °S)

- Aura/MLS (Microwave Limb Sounder v3.3)

- HALOE (HALogen Occultation Experiment v19)

- ACE-FTS (Atmospheric Chemistry Experiment –

Fourier Transform Spectrometer v2.2)

2 3-D chemical transport models

- SLIMCAT

National Centre for Atmospheric Science, University of Leeds

- KASIMA

(28)

Lati

tude

s

-> HCl relative rates of change for 8 NDACC sites

Ground-based measurements Satellite data

SLIMCAT simulation SLIMCAT run with constant 2000 meteorological forcing

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Lati

tude

s

-> HCl relative rates of change for 8 NDACC sites

Northern

Hemisphere

sites

(30)

-> Evolution of stratospheric HCl from satellite observations

≈ 30 km altitude

(upper stratosphere)

≈ 20 km altitude

(lower stratosphere)

(31)

-> Evolution of stratospheric HCl from satellite observations

≈ 30 km altitude

(upper stratosphere)

≈ 20 km altitude

(lower stratosphere)

Southern Hemisphere Northern Hemisphere

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-> Evolution of stratospheric HCl from satellite observations

≈ 30 km altitude

(upper stratosphere)

≈ 20 km altitude

(lower stratosphere)

Southern Hemisphere Northern Hemisphere

(33)

-> Evolution of stratospheric HCl from satellite observations

≈ 30 km altitude

(upper stratosphere)

≈ 20 km altitude

(lower stratosphere)

Southern Hemisphere Northern Hemisphere

(34)

-> Evolution of stratospheric HCl from satellite observations

≈ 27 km altitude

(upper stratosphere)

≈ 19 km altitude

(lower stratosphere)

Southern Hemisphere Northern Hemisphere

E Mahieu et al. Nature 515, 104-107 (2014) doi:10.1038/nature13857 Sources: Fahey, D.W., and

(35)

-> Spatial distribution of the HCl concentration and age-of-air changes

Between 2010/2011 and 2005/2006

(36)

-> Spatial distribution of the HCl concentration and age-of-air changes

Between 2010/2011 and 2005/2006

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-> Spatial distribution of the HCl concentration and age-of-air changes

Between 2010/2011 and 2005/2006

(38)

-> Spatial distribution of the HCl concentration and age-of-air changes

Slowdown in the

Northern Hemisphere atmospheric circulation

More aged air to the lower stratosphere

Larger relative conversion of source gases to HCl

(39)

Conclusion

- The Montreal protocol is still on track

=> HCl over the 1997 – 2011 period = -0.5 %/yr

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Conclusion

- The Montreal protocol is still on track

=> HCl over the 1997 – 2011 period = -0.5 %/yr

=> overall reduction of the stratospheric chlorine loading

- Short-term dynamical variability

=> influence on other stratospheric tracers? => causes still unindentified

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