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Investigation of the oxygen isotope exchange between carbon dioxide and ozone via O(_1hn1D) [Elektronische Ressource] / presented by Robina Shaheen

128 pages
DISSERTATIONsubmitted to th e Combined Faculty for t he Natural S ciences and for M athmeticsof the Rup erto-Carola Univ ersity of Heidelberg, Germanyfor th e de gree ofDo ctor of N atural Sci encespresented b yMS in Chemistry: Robi na Shah eenborn in F aisalabad, Pakis tanOral examination: 28.10.2005iInvestigation of the Oxygen Isotope Exchange Between Carbon Dioxide and Ozone 1via O(D) Referees: Pr of. Dr. Tho mas Rö ckmann Prof. Dr. Wolf gang K rätschmeriiErklärung g emäβ § 7 (3 ) b) und c ) de r P romotionsordnung:a) Ich erkläre hiermit, dass ich die vorgelegte Diss ertation selbst verfasst und mich dabeikeineranderen a ls de r von m ir ausdrücklich b ezeichneten Q uellen b edient ha be.b) Ich erkläre hiermit, dass ich an keiner anderen Stelle ein Prüfungsverfahren beantragtbzw. die Diss ertation in dieser oder anderer Form bereits anderweitig als Prüfungsarbeitverwendet od er ein er anderen Fakultät a ls Dissertation vor gelegt ha be.________________________ Robina Shahe eniiiAbstractCarbon dioxide in the middle atmosphere shows an increasing enrichment in the heavy17 17oxygen isotopes with altitude which preferential enrichment for O according to O =1.718 17 18O. This is contrary to tropospheric CO where O ~ 0.5 O. These isotope enrichments2are transferred from O into CO , but details of the mechanism are not understood yet.
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DISSERTATION
submitted to th e
Combined Faculty for t he Natural S ciences and for M athmetics
of the Rup erto-Carola Univ ersity of Heidelberg, Germany
for th e de gree of
Do ctor of N atural Sci ences
presented b y
MS in Chemistry: Robi na Shah een
born in F aisalabad, Pakis tan
Oral examination: 28.10.2005
iInvestigation of the Oxygen Isotope Exchange
Between Carbon Dioxide and Ozone
1via O(D)
Referees: Pr of. Dr. Tho mas Rö ckmann
Prof. Dr. Wolf gang K rätschmer
iiErklärung g emäβ § 7 (3 ) b) und c ) de r P romotionsordnung:
a) Ich erkläre hiermit, dass ich die vorgelegte Diss ertation selbst verfasst und mich dabei
keineranderen a ls de r von m ir ausdrücklich b ezeichneten Q uellen b edient ha be.
b) Ich erkläre hiermit, dass ich an keiner anderen Stelle ein Prüfungsverfahren beantragt
bzw. die Diss ertation in dieser oder anderer Form bereits anderweitig als Prüfungsarbeit
verwendet od er ein er anderen Fakultät a ls Dissertation vor gelegt ha be.
________________________
Robina Shahe en
iiiAbstract
Carbon dioxide in the middle atmosphere shows an increasing enrichment in the heavy
17 17
oxygen isotopes with altitude which preferential enrichment for O according to O =1.7
18 17 18
O. This is contrary to tropospheric CO where O ~ 0.5 O. These isotope enrichments2
are transferred from O into CO , but details of the mechanism are not understood yet. A3 2
systematic study was carried out using O and CO gases of different isotopic composition.2 2
Results show the existence of a photochemical isotope equilibrium between O and CO,2 2
17which is independent of the initial isotopic composition and shows equal enrichments for O
18
and O. Additi onal experiments were conducted to investigate the effect of temperature,
pressure and O/CO ratio. Dat a revealed that the magnitude of enrichment at photochemical2 2
equilibrium depends on pressure and on O/CO ratios with a decrease in enrichment at higher2 2
pressures. Also, the enrichment in CO showed a positive temperature dependence. The2
measurement of asymmetric O in one experiment yields additional insight into the isotope3
*exchange mechanism and shows the absence of anomalous fractionation steps in the CO 3
intermediate. The experimental data were modeled with the chemical kinetics software
Facsimile. In addition, a large set of new measurements of the isotopic composition of
stratospheric CO are presented, extending the e arlier d ata do wn to the tropopause.2
Zusammenfassung
In der mittleren Atmosphäre zeigt Kohlendioxid eine An reicherung in den schweren
17Sauerstoffisotopen, die mit der H öhe zunimmt wobei O bevorzugt in CO zu finden ist. Es2
17 18ergibt sich der ungewöhnliche Zusammenhang O =1.7 O. Für troposphärisches CO 2
17 18
dagegen gilt: O ~ 0.5 O. Di ese Isotopenanreicherungen werden von O in CO3 2
übertragen, aber die Details des Isotopentransfers sind noch nicht verstanden. In dieser Arbeit
wurde eine systematische Studie unter Verwendung von O und CO unterschiedlicher2 2
Isotopenzusammensetzung durchgeführt. Di e Er gebnisse zeigen ein photochemisches
Isotopengleichgewicht zwischen O und CO , das unabhängig von der anfänglichen2 2
17 18
Isotopenzusammensetzung ist und ähnliche An reicherungen für O und O aufweist. Weitere
Experimente zum E influss von Temperatur, Druck und Mischungsverhältnis wurden
durchgeführt. Die Anreicherungen im photochemischen Gle ichgewicht sind abhängig vom
Druck und dem O/CO Verhältnis und nehmen mit zunehmendem Druck ab. Sie zeigen2 2
außerdem eine positive Temperaturabhängigkeit. Di e Messung von asymmetrischem Ozon in
iv
ddddddddeinem Experiment liefert zusätzliche E insichten in den Isotopenaustauschprozess und zeigt,
*
dass keine anomalen Isotopeneffekte im intermediären CO Komplex auftreten. Di e3
experimentellen Da ten wurden mit de r Soft ware Facsimile modelliert. Zusätzlich werden neu e
Isotopenmessungen von stratosphärischem CO vorgestellt, die die vorhandenen Messungen2
bis zur T ropopause v ervollständigen.
vWho created se ven he avens in ha rmony.
Thou c an't s ee no fa ult in Beneficent One 's c reation; then look again:
can't thou se e any rift.
(Al -Qu ran 67:3)
viTable of Contents
1 I ntroduction..............................................................................................................................3
1.1 Objectives.........................................................................................................................6
2 Background and Th eory...........................................................................................................8
2.1 I sotope e ffects...................................................................................................................8
2.1.1 E quilib rium mas s-dependent isotop e fractiona tion..................................................9
2.1.2 Kinetic mass-d ependent isotop e fractionati on........................................................12
2.1.3 Anomalous or m ass ind ependent isotop e fractiona tion..........................................13
172.1.4 Mass dep endent fractionati on lin e: sl ope a nd O d efinition................................15
2.2 CO in th e atmosphere....................................................................................................172
2.2.1 Stratosph eric CO ...................................................................................................192
2.2.2 I mplication of th e s tratospheric CO anomal y202
2.3 Ozone ..............................................................................................................................21
2.3.1 I sotope e ffect i n oz one............................................................................................22
2.3.2 Pressure and t emperature e ffect..............................................................................24
2.3.3 Ozone in atmosphere..............................................................................................25
3 Experimental T echniques.......................................................................................................26
3.1 I sotope Ratio Mass S pectrometry...................................................................................26
3.1.1 Principle..................................................................................................................26
3.1.2 Sample Inlet............................................................................................................28
3.2 Analysis of CO isotopes................................................................................................292
3.2.1 Ce O exch ange system312
3.2.2 Preparation of t he Ce O reactant.............................................................................322
3.2.3 Ca libration o f C eO exch ange system....................................................................332
3.3 Produ ction of M IF CO from O....................................................................................342 2
3.4 CO and O isotope exc han ge expe riments...................................................................362 3
3.5 Photol ysis c onstants........................................................................................................38
3.5.1 T ime profil e of O fo rmation..................................................................................393
3.5.2 T ime profil e fo r O disso ciation413
3.6 CO extr action method ..................................................................................................422
3.7 N O correction................................................................................................................472
4 Photoch emical Equi libr ium between Carbon D ioxide an d Ozone ........................................49
4.1.1 B lank e xperiments50
4.1.2 T emporal e volution of CO and O isotopi c ex change...........................................502 3
4.2 Photo ch emical eq uilibrium between CO and O........................................................522 3
4.3 Discussion......................................................................................................................55
5 T emperatu re and Pr essure Dependence of th e Isotope Exchan ge Reaction...........................63
5.1 T emperatu re ef fect .........................................................................................................63
5.1.1 B lank e xperiments..................................................................................................63
5.1.2 L ow temperatu re exp eriments w ith th e Oriel lamp................................................63
5.1.3 L ow temperatu re exp eriments w ith th e Pur itech l amp64
5.2 Photoch emical eq uilibrium (triangulation expe riments) a t low t emperatu re.................68
5.3 Enrichment in CO as a fun ction of p ressure and O /CO ratio......................................702 2 2
5.4 Effect of ot her g ases on t he CO -O isotop e exch ange...................................................732 3
5.4.1 E ffect of N.............................................................................................................732
5.4.2 E ffect of NO..........................................................................................................742
5.5 Effect of phot olysis w avelength ....................................................................................75
5.6 Discussion......................................................................................................................76
1
D6 Stratospheric Carbon Dioxide ...............................................................................................83
6.1 L ong te rm stability of th e extr action s ystem .................................................................83
6.2 Ev alu ation of d ata qualit y..............................................................................................84
6.3 Stratosph eric CO samples .............................................................................................852
6.4 Discussion.....................................................................................................................88
7 Photoch emical B ox Mod el....................................................................................................90
7.1 G eneral d escription.........................................................................................................90
7.2 Mod eling of ozone r ate co efficients...............................................................................94
7.3 Simulation of l ab expe riments........................................................................................96
7.4 I mplications of l aboratory results to st rato spheric CO................................................1012
7.5 Mod el sensitivity test102
7.6 Discussion....................................................................................................................103
8 Summar y and Conclusions .................................................................................................108
9 Biblio graphy........................................................................................................................111
10 App endix I.........................................................................................................................118
11 Acknowledgements............................................................................................................121
2 1 I ntroduction
1 Introduction
Th e study of atmospheric dynami cs such as stratosphere-troposphere exchange and
strato spheric mixing processes has focused on concentration measurements of inert trace
gases with long life time such as CO, NO and halogenated compounds such as SF , CF and2 2 6 4
the chlorofluorocarbon s (CFCs) [Boering et al.1996, M aiss et al. 1996]. M ass independent
anomalies obse rved in the multi- oxygen isotopic measurements of stratospheric and
mesospheric CO offer another potential tracer of upper atmos phere dynamics [Boering et al.2
2004, Alexande r et al. 2001, Lämmerzahl et al. 2002, Thiemens et al. 1995a, b]. The anomal y
can also be used as a tracer of terrestrial gross carbon fluxes on a decadal to millienial time
scales[Hoa g et al. 2005, Luz et al. 1999 ] because it is directly related to gross primar y
productivity. Howev er, a prerequisite for the qua ntitative application of three-isotope
technique to study strato spheric trans port and chemistry is a thorough understandin g of the
anomalous isotop e excha nge mecha nism, whi ch is still missing.
Most isotopic fractionation processes such as diffusion, evaporation -condensation and kinetic
effects depends on the ma sses of the molecules involved. For oxygen with three stable
17 18 17 18isotopes, this le ads to a correlation b etween O and O as O ~ 0.5O. H ere th e c ommonly
17 16 18 16
used delta ( ) valu es denote the relative devia tions of the isotope ratios O/ O and O/ O
17 18( R and R, respectively) in a sample (R ) from a standard mat erial (R ) in permill (‰), e.g.s st
17 17 17O = (R / R -1)*1000‰.s st
Fractionation processes which do not ob ey this relation are called "anomalous " or "m ass
17 18independent" (for details se e s ec. 2.1.3 ). On a three isotope plot of O (ordinate) versus O
(abscissa) mass dependent fractionati on processes define a line with slope of ~0.5 that passes
through the origin (Vienna Stand ard Me an Ocean Wate r). A mass independently fractionated
compound will not lie on this mass dependent fractionat ion (MD F) line as shown in Figure
1.1.
Sinc e the startling discovery of the anomalous fractionation in ozone [M auer sberger 1981,
1987], in the stratosphere and laborato ry [Thie mens and Heidenreich 1983] anomalous
compositions have been obs erved in many other atmospheric trace species such as NO, CO,2
-2
HO, SO [Brenninkmeijer e t al.2003] (for d etails see s ec. 2.1.3 ). 2 4
3
dddddd1 I ntroduction

140
S tratospheric O
3
S tratospheric CO120 2
Tropospheric C O
2
Tropospheric O
2
100
80
60
MDF lin e
40
20
0
0 20 40 60 80 10 0 120 14 0 160 180
18
O (‰)
SMOW
17 18 17 18Figu re 1.1: Three isotope plot with MDF line ( O ~ 0.5 O). S tratospheric ozone ( O ~ 0.6 O)
17 18
[Kranko wsky et al. 2000], stratospheric CO ( O ~ 1.6 O) [L ämmerzahl et al. 200 2]. Tropospheric CO and2 2
O are also shown for c omparison. 2
Tropospheric CO possesses a ma ss dependent isotopic composition (Figure 1.1) tha t is2
controlled by the bios phere, mostly through exchange with wat er within leaf stomata [Fr anc y
and Tans 1987] and soil water [Tans 1998]. How ever upon entering the stratosphere, CO2
1acquires a mas s independent anoma ly from O via O(D) through the following sequence of3
reactions:
1O + h g (O D) + O l < 310 nm (R1 ) 3 2
1 *CO + O(D) g CO (R2)2 3
* 3
CO g CO + O(P) (R3)3 2
* 1
COg CO + O(D) (R4)3 2
Th e surprising obs ervation is that the isotope anomal y in strato spheric CO is unique. In2
17 18contrast to ozone and various other subst ances related to ozone, where the O and O
17 18
enrichments are approximatel y equal, stratos pheric CO follows the relation O ~ 1.7 O,2
which has the highest three isotope slope obs erved in a natu ral system [Lämmerzahl et al.
17 18
2002]. This means tha t O is pr eferentially in corporated in to CO compa red to O. 2
4
dddddddnddd
17
O (‰)
SMOW

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