Stratospheric Chemistry and Processes. Sophie Godin-Beekmann LATMOS, OVSQ, IPSL

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1 Stratospheric Chemistry and Processes Sophie Godin-Beekmann LATMOS, OVSQ, IPSL 1

The Stratosphere Layer just above the troposphere Altitude depends on latitude and season (higher in the tropics and summer) ~10% of atmospheric mass Positive

2 The Stratosphere Layer just above the troposphere Altitude depends on latitude and season (higher in the tropics and summer) ~10% of atmospheric mass Positive gradient of temperature due to solar UV radiation absorption by molecular oxygen and ozone Slow mixing in the vertical Chemical processes linked to the presence of ozone 2

The ozone layer Ozone vertical distribution

of ozone Absorbs UVB radiation 280 320 nm Heats

atmosphere molecules: ~8 km Ozone formation in

3 The ozone layer Ozone vertical distribution Ozone column abundance 90% 10% Main properties of ozone Absorbs UVB radiation nm Heats the stratosphere Strong oxidant All ozone molecules compressed to P ~1 atm. and T=0 C: Layer of 3 mm thickness (300 DU) All atmosphere molecules: ~8 km Ozone formation in the atmosphere ~500 millions years ago allowed life to emerge from the ocean 3

Ozone equilibrium: chemical processes Production O 2 O 2 + hn O + O l < 242 nm O + O 2 + M O 3 + M (+DQ) R1 R2 Chapman mechanism proposed in 1930 by Sydney Chapman Loss O 3 +

4 Ozone equilibrium: chemical processes Production O 2 O 2 + hn O + O l < 242 nm O + O 2 + M O 3 + M (+DQ) R1 R2 Chapman mechanism proposed in 1930 by Sydney Chapman Loss O 3 + hn O + O 2 O + O 3 2 O 2 l < 310 nm R3 R4 Chapman mechanism successful in reproducing general shape of ozone layer but: explains only 20% of the loss of Ox in the stratosphere 4

5 Ozone loss: catalytic cycles R4 reaction (O + O 3 -> 2O 2 ) too slow in chapman mechanism: Other mechanisms introduced to explain the loss of O x via Catalytic cycles O 3 + X XO + O 2 O + XO X + O 2 net: O + O 3 2 O 2 NO x HO x ClO x BrO x Catalytic cycles can occur 1000 times N 2 O CH 3 Cl & CFCs: CF 2 Cl 2 CF 3 Cl H 2 O CH 4 Methyl bromide & Halons Catalytic agents produced from source gases transported to the stratosphere by dynamic processes N 2 O, CH 4, H 2 O, CH 3 Cl, CH 3 Br CFCs, Halons 5

6 Overview of chemical processes Example: NO x cycle N 2 O + hn N 2 + O 1D R1 or N 2 O + O 1D N 2 + O 2 R2 NO + NO R3 R3: only 5% of N 2 O loss but only source of NO x radicals Catalytic cycle NO + O 3 NO 2 + O 2 NO 2 + O NO + O 2 Net O + O 3 2 O 2 Rapid exchange of NO-NO 2 NO x family Formation of reservoir species limits efficiency of the cycles: HO 2 + HO 2 H 2 O 2 + O 2 ClO + NO 2 + M ClONO 2 + M NO 2 + OH + M HNO 3 + M BrO + NO 2 + M BrONO 2 + M Cl + CH 4 HCl + CH 3 6

7 Fragile ozone equilibrium Atmospheric abundance of main atmospheric species Ozone controled by species 1000 time less abundant!! abundance of radical species 44 N, zenith angle: 60 Reprobus model HO x ClO x NO x BrO x 7

8 Efficiency of catalytical science Efficiency of main catalytic cycles Ozone photochemical lifetime Lower stratosphere: ozone controlled by dynamical processes 8

by the meridional stratospheric circulation Total ozone

9 Ozone equilibrium : dynamical processes Mainly produced in the tropics, ozone is transported towards the poles by the meridional stratospheric circulation Total ozone climatology Brewer-Dobson circulation Planetary waves 9

10 The perturbed ozone layer Antarctic Ozone hole October

11 First alerts on the ozone layer 1970s: controversy on the impact on ozone of a fleet of stratospheric supersonic transports 1974: article of Molina and Rowland The SST project is abandoned (except for the UK-French Concord) Catalytic destruction of ozone by chlorofluorocarbons (CFC) 1979: aerosol sprays are banned by USA, Sweden, Canada 11

12 Substances depleting the ozone layer (SDO) Halons Chlorofluorocarbons (CFC) patent in 1928 by DuPont (USA) - Main CFC: CFC-11 (CCl 3 F), CFC-12 (CCl 2 F 2 ) Long lifetime -> transported in the stratosphere by atmospheric dynamical processes Applications : refrigeration, air conditioning, blowing agents... wonder chemicals! Organic brominated gases Main halons: halon-1211 and halon-1301 Applications : dry cleaning, fire extinguishers Natural sources of chlorine and bromine in the stratosphere CH 3 Cl (methyl chlorid) et CH 3 Br (methyl bromid): emitted by terrestrial and oceanic ecosystems. 12

.. First report on the state of the ozone layer But signature

13 Early 1980s Evolution of knowledge on impact of CFCs on ozone Effect of CFC on ozone CFC emissions grow again... First report on the state of the ozone layer But signature of the Vienna Convention for the protection of the ozone layer in

Ozone hole discovery in Antarctica Syowa At Syowa,

, Large Losses of total ozone in Antarctica reveal

14 Ozone hole discovery in Antarctica Syowa At Syowa, total ozone and sonde measurements show also large decreases in Spring Chubachi et al., QOS, 1984 Farman et al., Large Losses of total ozone in Antarctica reveal seasonal ClO x /NO x interaction, Nature, 1985 TOMS Total Ozone monthly average Stolarski et al., Nature,

Elucidation of ozone destruction mechanisms Before 1985 : Ozone theory based on chemical processes in gaseous phase only Antarctica : ozone loss rate : ~5 % per day, not explainable by theory

15 Elucidation of ozone destruction mechanisms Before 1985 : Ozone theory based on chemical processes in gaseous phase only Antarctica : ozone loss rate : ~5 % per day, not explainable by theory Hypothesis : Chemical reactions at the surface of polar stratospheric clouds: Activation of chlorine compounds(solomon, 1986) Very fast catalytical cycles (Molina & Molina, 1987) O 3 August ClO pôle Scientific proof September Anderson et al., 1991 NASA campaign: Airborne Antarctic Ozone expedition 1987 ER-2 stratospheric plane 15

Polar ozone destruction mechanism I n darkness In the light of the rising spring sun 1 2 Formation of polar stratospheric clouds: HNO 3 Activation of Cl x : ClONO 2 HOCl N 2 O 5 H 2 O HNO 3 Cl2,HOCl

16 Polar ozone destruction mechanism I n darkness In the light of the rising spring sun 1 2 Formation of polar stratospheric clouds: HNO 3 Activation of Cl x : ClONO 2 HOCl N 2 O 5 H 2 O HNO 3 Cl2,HOCl H 2 O HCl cold, isolated polar vortex -80 C Formation of ClO x : Cl 2 + hn HOCl + hn 2Cl OH + Cl Cl + O 3 ClO + O 2 Catalytic ozone depletion: ClO + ClO Cl 2 O 2 Cl 2 O 2 + hn 2Cl + O 2 Cl + O 3 ClO + O Complete total O 3 destruction between 14 and 20 km Stratosphere 9 km Troposphere Antarctica 2060:12.8b:1/96:blm Ingredients for the formation of the ozone hole: 1. Increase chlorine and bromine content in the stratosphere (Cl y x 5) 2. Isolated polar air masses in winter (polar vortex) 3. Very low temperatures(< - 80 C) 16

Polar stratospheric clouds CALIOP backscatter Main PSC particles: Supercool ternary solution (STS), Nitric Acid trihydrate (NAT) and ice Main heterogeneous

17 Polar stratospheric clouds CALIOP backscatter Main PSC particles: Supercool ternary solution (STS), Nitric Acid trihydrate (NAT) and ice Main heterogeneous reactions: depolarisation Peter, Convert chlorine and bromine reservoir species into more reactive forms - HCl, HNO 3 and H 2 O remain in the particles 17

+ ClO Br + Cl + O Cycles need ClO > 1 ppbv to be

18 Polar chemistry Denitrification and dehydration observed by MLS Main catalytic cycles ClO + ClO + M ClOOCl +M BrO + ClO Br + Cl + O Cycles need ClO > 1 ppbv to be efficient Antarctic winter-spring 2006 Destruction rate: ~5 % /day 18

19 The Montreal Protocol Signed in 1987 entered into force in 1989 Regulation of CFC and brominated halons emissions -> Substitutes less toxic for the ozone layer (First HCFC then second HFC that don t contain chlorine) Technology transfer towards developing countries Regular reports on the state of the ozone layer and substitutes productions: the evolution of the protocol depending on scientific results Multilateral fund for technological transfers : ~ 4 billions dollars in 2014 Reference for the creation of IPCC in 1988 related to climate change

20 Montreal Protocol Amendments «Science driven» protocol : CFC HCFC

21 Ozone Destruction in the Arctic? Polar Stratospheric Clouds Formation of stratospheric clouds but polar vortex in the Arctic less isolated and warmer: polar ozone loss weaker and more variable

22 Arctic ozone loss Various international campaigns to quantify ozone loss : AASE, EASOE, SESAME, THESEO-SOLVE, RECONCILE Various measurements and methods (more difficult to distinguish chemical loss from dynamical loss): Match, passive ozone tracer Arctic ozone loss in 1999/2000 compared to typical Antarctic ozone loss WMO,

23 Chlorine activation in cold arctic winters HCl ClO O 3 AURA MLS measurements of HCl, ClO and O 3 Santee et al., /

24 Ozone depletion at global scale Total ozone trends Trend vertical profile Ground-based Satellite WMO, 1998 Fioletov et al., 2002 No trends in the tropics Mid-latitude ozone trends due to dilution of polar ozone loss, chemical in situ processes and change in meteorology 24

Effect of volcanic stratospheric aerosols Aerosol integrated backscatter 694.

25 Effect of volcanic stratospheric aerosols Aerosol integrated backscatter nm El Chichon Pinatubo Lidar (Garmisch) Sage II Mt Pinatubo eruption, June 1991 Significant injection of ~20 MT of SO 2 that converted into H 2 SO 4 aerosol droplets Main heterogeneous reactions on strat aerosols Increases sensitivity of ozone to ClOx and decreases sensitivity to NOx High chlorine levels: decrease of O 3 Low chlorine: increase of O 3 Pinatubo aerosol effect on ozone A few % temporary decrease 25

26 Present state of the ozone layer 27 years after enforcement of Montreal Protocol 26

27 Evolution of CFC and halons content EESC: Evolution of stratospheric halogen content weighted by the toxicity of species towards ozone 27

28 Evolution of Antarctic ozone hole Ozone hole area Minimum d ozone Ozone hole: Recurrent seasonal feature in Southern Hemisphere since

29 Ozone evolution at global scale Annual ozone anomalies (with respect to means) WMO,

30 Evolution of polar ozone Ozone minimum values in March (Arctic) and October (Antarctic) Record Arctic ozone loss in : major warming in Antarctica 30

31 Record Arctic ozone depletion 2011 IASI total ozone 25 % additional ozone loss due to denitrification Low ozone also explained partly by low ozone transport to the pole Manney et al., Nature 2011 also Sinnüber et al., 2012; Kuttipurath et al.,

32 Looking for ozone recovery due to decrease of ODS 32

Quantification of ozone variability Multiple regression models TOZ(t)=TOZ + a EESC EESC(t)+Sa i Proxy i (t) + residual(t) Main proxies used - QBO (30 & 10 hpa) - NAO or ENSO

33 Quantification of ozone variability Multiple regression models TOZ(t)=TOZ + a EESC EESC(t)+Sa i Proxy i (t) + residual(t) Main proxies used - QBO (30 & 10 hpa) - NAO or ENSO index - Solar flux - Eddy heat flux averaged over N or S (BDC) - aerosol optical depth - EESC or PWLT (piecewise linear trend with turning point around ~1996) 33

34 Influence of proxies (polar regions) ± 4 DU ± 5 DU ± 10 DU Linear relationship between Spring/Fall ozone ratio and eddy heat flux Weber et al., 2011; Weber et al.,

35 Ozone recovery in Antarctica 1 st stage recovery 2 nd stage recovery Yang et al., JGR, 2008 Identification of second stage recovery claimed by Salby et al., GRL, 2011; JGR, 2011; Kuttipurath et al., 2013, and Knibbe et al., 2014 De Laat (2015) use «big data approach» to trace recovery, e.g. MC on period, proxy, etc..: 30 60% of the regressions result in statistically significant positive springtime ozone trend over Antarctica Solomon et al., 2016 Significant recovery in September increases in ozone column amounts and vertical profile decreases in the area of the ozone hole 35

, ACP, 2015 error bars: black: std of weighted average red: Joint distribution light blue: drifts taken into account no

36 Ozone recovery in the upper stratosphere? Past changes in the vertical distribution of ozone : Analysis and interpretation of trends Harris et al., ACP, 2015 error bars: black: std of weighted average red: Joint distribution light blue: drifts taken into account no significant upward trends different conclusion from WMO, 2014 NDACC Alpine station (OHP, Hohenpeissenberg, Bern) more than 2 decades of measurements temporal instrumental artefacts vs geophysical signals: 3%/decade range in trends Godin-Beekmann et al., 2016

BDC : Decrease of ozone in the LS in the 1980s (e.g. Randel and Thompson, 2011; Sioris et al, 2014, Shepherd et al.

37 Global ozone trends ODS decrease Climate change effect: Acceleration of Brewer-Dobson circulation -> decrease of ozone in tropics -> increase of ozone in extratropics WMO, 2014 Contrasted trends observed in Evidence for an increase of the lower branch of the BDC : Decrease of ozone in the LS in the 1980s (e.g. Randel and Thompson, 2011; Sioris et al, 2014, Shepherd et al., 2014) but: Hiatus in upwelling since 2002 from SAGEII + SCIAMACHY + SHADOZ ozone observations (Aschmann et al., 2014) Increase of ozone in the troposphere?

38 Main drivers of ozone long term changes 38

Ozone changes and climate transport Sun drives radiative, dynamical and chemical processes affecting ozone and temperature Stratospheric temperature determined by concentrations of radiatively active

39 Ozone changes and climate transport Sun drives radiative, dynamical and chemical processes affecting ozone and temperature Stratospheric temperature determined by concentrations of radiatively active gases (ozone, long-lived greenhouse gases, H 2 O) and aerosols via absorption of SW and LW radiation Transport determines amounts of stratospheric ozone and related long-lived compounds Temperature influences temperature-dependent reaction rates 39

Forecasted evolution of EESC Equivalent effective stratospheric chlorine mid-latitudes Polar Total chlorine abundance at Jungfraujoch (x10 15 mol.cm -2 ) Newman et al.

40 Forecasted evolution of EESC Equivalent effective stratospheric chlorine mid-latitudes Polar Total chlorine abundance at Jungfraujoch (x10 15 mol.cm -2 ) Newman et al., acp, 2007 Rate of decline depends on atmospheric lifetime of halogen compounds In the Polar regions age of air larger than in mid-latitude regions Return date to 1980 : Mid-latitudes 2040 Polar regions

41 Source gases evolution IPCC 2007 WMO, GHG report abundance relative to year 1750 of CH 4 and N 2 O: CH 4 : 256% N 2 O: 121% CFC and HCFC abundances regulated by the Montreal Protocol 41

42 Evolution of stratospheric aerosols Tenfold increase of aerosols due to large volcanic eruptions (e.g. El Chichon, Pinatubo) induces a temporary ozone decrease (in the presence of large ODS levels) Since 2000: temporary increase of background aerosol due to small volcanic eruption 20 S 20 N Vernier et al., GRL, 2011 Radiative forcing (RF) of volcanic eruptions for the years of ~ W m -2 (Solomon et al., 2011) Looking for new stratospheric aerosol background: volcanos vs impact of asian pollution NH mid-latitudes & OHP (44 N, 6 E) SAOD 17-30km Khaykin et al., 2016 Non volcanic period: 17% increase 42

Evolution of stratospheric temperature Global mean temperature anomalies from multiple data sets 10 25 km SSU temperature anomalies Global-mean lower stratosphere cooled by 1 2 K from 1980

43 Evolution of stratospheric temperature Global mean temperature anomalies from multiple data sets km SSU temperature anomalies Global-mean lower stratosphere cooled by 1 2 K from 1980 to 1995 Upper stratosphere cooled by 4 6 K from 1980 to about No significant long-term trend since Cooling of stratosphere due to stratospheric ozone depletion and GHG increase 43

44 Effect of stratosphere cooling on ozone Homogeneous chemistry 45 N for equinox conditions (end of March) 40 km 20 km Slows ozone destruction rates, e.g. O + O 3 2O 2 at 40 km -> ozone increase Heterogeneous chemistry Potential increase of PSC in polar regions Larger effect in the Arctic region (unsaturated ozone loss) 44

Stratospheric water vapor No recent increase in stratospheric water vapor at global scale Mechanisms driving long-term changes in stratospheric water vapor

45 Stratospheric water vapor No recent increase in stratospheric water vapor at global scale Mechanisms driving long-term changes in stratospheric water vapor not well understood. Hartman et al., 2013, WMO, 2014 Effect on ozone Increase in HO x Increases temperature threshold for PSC formation in polar regions 45

46 Simulation of ozone recovery by climate models 46

47 Future ozone evolution: summary Shepherd and Jonsson, acp, 2007 ODS O3 destruction CO 2 cools the stratosphere + impact on circulation (GHG) N 2 O O 3 destruction (NO x cycle) CH 4 O 3 destruction + impact on circulation Fleming et al., 2011, Portmann et al.,

48 Tropical regions Ozone less sensitive to ODS Sensitive to BDC Decrease in stratosphere? Increase in troposphere? Observations? Eyring et al., JGR,

Polar ozone Antarctic: return of October total

49 Polar ozone Antarctic: return of October total column ozone to 1980 projected after mid century Arctic: return of March-mean Arctic total column ozone projected in RCP: Climate change dominates polar ozone evolution after 2050 Larger sensitivity in NH 49

50 Some take home messages Montreal protocol successful in reducing the amount of ozone depleting substances (ODS) in the atmosphere but the return to pre-1980 levels will take decades The ozone layer should return to pre-1980 levels by depending on latitudes and climate change effects Models predict by 2100 a super-recovery of ozone at mid-latitude and polar regions and an under-recovery in the tropics In the polar regions: competition between stratospheric cooling and decrease of ODS in the next decade. Also changes in meteorologic variability Future threat to the ozone layer: geoengineering by sulfate aerosols injection into the stratosphere Evaluation of future ozone levels needs an adequate ozone monitoring system: issues both in satellite and ground-based observing systems 50

51 Thank you! Polar Stratospheric Cloud observed at Haute- Provence Observatory on February 3,

SCIAMACHY book. Ozone variability and long-term changes Michel Van Roozendael, BIRA-IASB

SCIAMACHY book. Ozone variability and long-term changes Michel Van Roozendael, BIRA-IASB SCIAMACHY book Ozone variability and long-term changes Michel Van Roozendael, BIRA-IASB 1928: start of CFC production 1971: 1 st observation of CFC in the atmosphere (J. Lovelock) 1974: identification