Isotope exchange between CO2 and O3 in the stratosphere: atmospheric and laboratory

measurements

Thomas RöckmannInstitute for Marine and Atmospheric Research UtrechtInstitute for Marine and Atmospheric Research UtrechtUtrecht UniversityUtrecht UniversityThe NetherlandsThe Netherlands

RobinaShaheen, USCD, La Jolla, CA, USAChristof Janssen, UPMC, Paris, France

OutlineOutline

Stratospheric observationsStratospheric observations

Proposed mechanismProposed mechanism

Laboratory experimentsLaboratory experiments

Conclusions and outlookConclusions and outlook

Stratospheric COStratospheric CO22 datadata

30 40 50 6015

20

25

30

35

40

45

s lope = 1.18

M DF tr opospheric CO 2 Th iem ens et a l., 1991 Th iem ens et a l., 1995

δ17 O

(‰

)

δ 18O (‰)

30 40 50 6015

20

25

30

35

40

45

s lope = 1.65 s lope = 1.18

M DF tr opospheric CO

2 Th iem ens e t a l., 1991 Th iem ens e t a l., 1995 Thiem ens et a l ., 1995b Zip f et a l., NA SA repor t A lexander et a l, 2001 Läm merzahl et a l, 2001 re jected

δ17 O

(‰

)

δ 18O (‰)

Boering 2004

Kawagucci, 2008

The link to ozoneO3 + hν→O(1D) + O2CO2+ O(1D) →CO3* →CO2 + O(3P) [Yung et al., 1991]

→CO2 + O(1D) [Perri et al., 2003]

Statistical exchange: Yung et al., 1991, 1997Mesospheric source: Thiemens et al., 1995, Liang et al., 2007MIF in CO3* complex: Wen&Thiemens, 1993, Johnston et al., 2000MDF in CO3* complex: Barth &Zahn, 1997

40 60 80 100 120 140 160

20

40

60

80

100

120

~ T=250K

~ T=188K

slope = 0.60

slope = 1.65

Strat CO2 Trop CO2 Strat O3

δ17 O

(‰)

δ18O (‰)

Possible influence of mesospheric O(1D)

Liang et al. 2007

Mesospheric O2 source: Lyman α photolysis

Internal and external factors in CO2 + O(1D) exchange

External: • O3enrichment (symmetric / asymmetric ?)• Fractionation in photolysis (O3→ O(1D))• O(1D) quenching• Non-quenching exchange

O(1D) reactant

nternal: •ractionation in CO3* complex (formation/dissociation)

Distribution of oxygen isotopes in O3

overall enrichment: 3E = 2A + S

asymmetric symmetric

measurements (Morton et al., JGR, 1990)

02468

10121416

100 150 200 250 300 350 400T (K)

E50,

E49

(%)

E50

E49

6 + 86 → 6866 + 76 → 676from theory

(Gao & Marcus, 2002)or experiment

(Janssen et al., 1999) making reasonable assumptions on 17O

calculate temp. dep.

Schematic view of fractionation process

Isotope equilibrium point studies

0 1500 3000 4500 6000 75000

20

40

60

80

100

120

140

δ 17O δ 18O

δ i O

(‰ )

Time (minutes)

Temporal evolution δ (t) = δeq – (δeq-δi) exp (-t/ teq)

Use δ values of CO2versus O2

Triangulation approach

0 40 80 120 1600

40

80

120

160

δ17 O

‰ (

fCO

2 - fO

2 )δ18O ‰ ( fCO2 - fO2 )

CO2-O3 mixture CO2-O2 mixture

-80 -40 0 40 80 120 160

-40

0

40

80

120

160

δ17 O

‰ (

fCO

2 - fO

2 )

δ18O ‰ ( fCO2 - fO2 )

δ17O = 0.56 δ18Oδ17O = 0.99 δ18Oδ17O = 2.95 δ18O

δ17O = 0.37 δ18Oδ17O = 1.09 δ18Oδ17O = -3.0 δ18O

Triangulation results

Isotope equilibrium well-definedNow examine dependency on reaction parameters

Chakraborty et al., 2003

CO2-O3 mixture CO2-O2 mixture

Link to asymmetric O3

Result: mass dependent fractionation between asymmetric O3 and CO2,eqOnly 1 measurement, low T (280K?)

Ratio of reactants: O2/CO2

0.1 1 10 10060

70

80

90

100

110

120

130

140

150

δ i O

O2 (

CO

2)

Ratio

δ 17O δ 18O δh(18O) = 146 + 4‰

δh(17O) = 142 + 4‰

δl(18O) = 64 + 11‰δl(17O) = 58 + 11‰

CO2 O2

External effect: CO2 affects O3 isotopic composition (better quencher)Non-quenching exchange?

Internal effect: 1:1 change -> MIF in CO3# complex?

T-dependence of Isotope Equilibrium

Asymmetric O3, T dependence:d17O: ~0.4‰/Kd18O: ~0.7‰/K

But: large corrections (errors) on T measurementRepeat with better T controlAlso pressure dependency!

Conclusions/outlookConclusions/outlook

Stratospheric COStratospheric CO22 possesses the highest possesses the highest oxygenoxygen--33--isotopeisotope--slope in natureslope in nature

Affects tropospheric reservoirAffects tropospheric reservoirTracer for Tracer for ““photochemical agephotochemical age””Origin of the OOrigin of the O22 isotope anomalyisotope anomaly

What is the exact slope in the stratosphere? What is the exact slope in the stratosphere? Variability close to tropopause?Variability close to tropopause?Decrease of slope at high altitudes?Decrease of slope at high altitudes?

Dynamics of the exchange processDynamics of the exchange processOrigin of slope 1.7?Origin of slope 1.7?Mass (in)dependent effect in COMass (in)dependent effect in CO33 complex?complex?External processes External processes –– relation to Orelation to O33??

INTRAMIFINTRAMIFINitialTRAining in Mass Independent FractionationA Marie Curie Initial Training Network

13 PhD projects

Utrecht UniversityUniversity of East AngliaUniversity of CopenhagenUniversity Pierre et Marie Curie, Paris,CEA-LSCE, ParisUniversity Joseph Fourier, GrenobleUniversity of Bern

http://www.phys.uu.nl/~intramif/

YeungYeung et al.: et al.: ΔΔ4747 measurementsmeasurements

vortex

mid-lat

Additional process: Additional process: Mesospheric photochemistry?Mesospheric photochemistry?Heterogeneous chemistry?Heterogeneous chemistry?

COCO22 + O(+ O(11DD) exchange:) exchange:Towards random Towards random distribdistrib..

Stratospheric CO2 dataInternal and external factors in CO2 + O(1D) exchangeDistribution of oxygen isotopes in O3Chakraborty et al., 2003