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| Titel |
Laboratory Measurements of High Resolution Photoabsorption Cross-Sections of Isotopologues of SO2 |
| VerfasserIn |
Douglas Blackie, Glenn Stark, James R. Lyons, Juliet C. Pickering, Peter L. Smith, Anne P. Thorne |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250057398
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| Zusammenfassung |
| The timing of the oxygenation of the Earth’s atmosphere is a central issue in understanding
the Earth’s paleoclimate. The discovery of mass-independent fractionation (MIF) of sulphur
isotopes deposited within Archean and Paleoproterozoic rock samples has given rise to a
possible marker, through the transition between MIF in older rock samples ( > 2.4 Gyrs) to
mass-dependent fractionation (MDF) in younger samples, for the rise in oxygen
concentrations in the Earth’s atmosphere [Farquhar,2003]. Laboratory experiments
[Farquhar,2001][Pen,2008] suggest isotopic self shielding during the gas phase photolysis as
the dominant mechanism for MIF. Self shielding is present for SO2 at wavelengths shorter
than 220 nm where it undergoes partial predissociation. The UV absorption of SO2 is
dominated by the ËC 1B2 - ËX 1A1 electronic system which consists of strong vibrational
bands extending from 170 - 230 nm. In an atmosphere consisting of low O2 and O3
concentrations, such as that predicted for the early Earth, UV radiation would penetrate deep
into the ancient Earth atmosphere in the 180 - 220 nm range driving the photolysis of
SO2.
We have conducted the first ever high resolution measurements of the photo absorption
cross sections of several isotopologues of SO2, namely 32SO2, 33SO2, 34SO2 and 36SO2. The
cross sections are being measured at Imperial College at initial resolutions of 1.0 cm-1, and
place special emphasis on the high relative accuracy of the measurements (< 3%), vital for
accurately modelling atmospheric processes. Further measurements at resolutions
of < 0.5 cm-1 are scheduled for inclusion in photochemical models of the early
Earth’s atmosphere. The models will be used to more reliably identify the processes
responsible for the sulphur isotope ratios found in ancient rock samples [Lyons,
2007]. 1.0 cm-1 resolution measurements of the four isotopologues of SO2 will be
presented in addition to preliminary < 0.5 cm-1 photo absorption cross section
measurements.
References:
Farquhar J & Wing BA, Earth and Planetary Science Letters, 213:1-13, 2003.
Farquhar J, Savarino J, Airieau S & Thiemens MH, JGR, 106:32829, 2001.
Pen A & Clayton RN, Geochimica et Cosmochimica Acta Supplement, 72:734,
2008.
Lyons JR, GRL 34:L22811, 2007. |
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