High‐precision spectroscopy of 32S, 33S, and 34S sulfur dioxide: Ultraviolet absorption cross sections and isotope effects

Danielache, Sebastian O.; Eskebjerg, Carsten; Johnson, Matthew S.; Ueno, Yuichiro; Yoshida, Naohiro

doi:10.1029/2007jd009695

Cited by 110 publications

(173 citation statements)

References 53 publications

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“…These shifts were based on vibrational wavefunctions calculated using a single ab initio SO 2 excited potential energy surface (11,12). However, SO 2 has a score of electronic states in the relevant energy region with multiple curve crossings, giving rise to the complicated pattern seen in the experimental results (13). For example, three vibronic peaks of the three isotopologues are found between 200 and 205 nm (Fig.…”

Section: Effect Of Atmospheric Uv Shielding On Isotopic Fractionationmentioning

confidence: 99%

“…Recent theoretical studies have examined the UV absorption spectra of SO 2 isotopologues (11) and have suggested that SO 2 self-shielding may have caused the Archean MIF record (12). However, the theoretical spectra necessarily contain several approximations and do not agree with recently obtained isotopologue-specific experimental spectra (13). The most straightforward way to determine the MIF effect is via direct measurement of UV absorption by SO 2 isotopologues.…”

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confidence: 99%

“…In a recent article, we presented the absorption spectra of three SO 2 isotopologues from 190 to 330 nm (13). Based on these spectra, we present here the multiple isotope fractionation factors for SO 2 photolysis as a function of wavelength.…”

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confidence: 99%

“…1 and Fig. S1) (13). Averaged over several nanometers, the mass independent isotope effect 33 E is generally negative at Ͼ 202 nm, and positive for Ͻ 202 nm (Fig.…”

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confidence: 99%

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Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox

Ueno

Johnson

Danielache

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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Distributions of sulfur isotopes in geological samples would provide a record of atmospheric composition if the mechanism producing the isotope effects could be described quantitatively. We determined the UV absorption spectra of 32 SO2, 33 SO2, and 34 SO2 and use them to interpret the geological record. The calculated isotopic fractionation factors for SO2 photolysis give mass independent distributions that are highly sensitive to the atmospheric concentrations of O 2, O3, CO2, H2O, CS2, NH3, N2O, H2S, OCS, and SO 2 itself. Various UV-shielding scenarios are considered and we conclude that the negative ⌬ 33 S observed in the Archean sulfate deposits can only be explained by OCS shielding. Of relevant Archean gases, OCS has the unique ability to prevent SO 2 photolysis by sunlight at >202 nm. Scenarios run using a photochemical box model show that ppm levels of OCS will accumulate in a CO-rich, reducing Archean atmosphere. The radiative forcing, due to this level of OCS, is able to resolve the faint young sun paradox. Further, the decline of atmospheric OCS may have caused the late Archean glaciation. mass independent fractionation ͉ carbonyl sulfide (OCS) ͉ sulfur dioxide (SO2) ͉ photochemistry ͉ greenhouse gases M ass independent fractionation (MIF) of sulfur isotopes has been found in geological samples older than 2.3 billion years (Ga) and is believed to be produced by the photochemical reactions of gaseous sulfur compounds in a low-oxygen reducing atmosphere (1-4). The rise of atmospheric oxygen (O 2 and O 3 ) would have oxidized atmospheric sulfur compounds to sulfate, preventing the accumulation of isotopic fractionation in two reservoirs. Moreover, it would have blocked UV sunlight inhibiting the supposed photochemical process(es) producing the isotope anomaly. In contrast, given reducing conditions, two isotopically distinct sulfur species such as elemental sulfur (polysulfur) and sulfate could be formed photochemically and precipitate at the surface, where the MIF signal could be preserved in sediment (3-5). Sulfur MIF in geological samples is regarded as indicating an anoxic atmosphere.This assertion relies on assumptions as to the origin of the MIF, although the mechanisms are still poorly known. Broad agreement in the ⌬ 36 S/⌬ 33 S ratio (ϷϪ1) in pre-2.3 Ga sedimentary rocks (1, 6, 7) and those produced in the laboratory by SO 2 photolysis suggest that photodissociation of gas-phase SO 2 most likely accounts for MIF in the Archean (2). Indeed, SO 2 photolysis is a key rate limiting step, particularly in a low-O 2 reducing atmosphere (4, 8). In addition, two mechanisms have been proposed whereby sulfur MIF could be formed under oxidizing conditions in the modern atmosphere: (i) Photolysis of SO 3 at altitudes greater than Ϸ50 km, where reaction between SO 3 and H 2 O is slow, is claimed to be responsible for the MIF found in modern stratospheric aerosol (8). In contrast, at lower altitudes, SO from SO 2 photolysis reforms SO 2 , so fractionation in SO 2 photolysis would not affect the isotopic compos...

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Section: Effect Of Atmospheric Uv Shielding On Isotopic Fractionationmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

“…1 and Fig. S1) (13). Averaged over several nanometers, the mass independent isotope effect 33 E is generally negative at Ͼ 202 nm, and positive for Ͻ 202 nm (Fig.…”

mentioning

confidence: 99%

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Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox

Ueno

Johnson

Danielache

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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144

124

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“…First, although the rate of SO 2 photolysis based on isotopologue-specific cross-sections in the region above the dissociation threshold at 220 nm do yield MIF fragments (18), the high concentration of O 2 in the modern atmosphere will rapidly reoxidize the SO to SO 2 , destroying any record of the process. Second, Pavlov et al (19) proposed that SO 3 photooxidation at wavelengths from 195 to 300 nm could explain sulfur MIF; however, in contrast to the highly structured SO 2 absorption spectrum, the absorption spectrum of SO 3 is smooth, reflecting direct photodissociation (20), and therefore, there is no physical reason why broadband solar photolysis of SO 3 would produce mass-independent enrichment.…”

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confidence: 99%

SO₂photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism

Hattori

Schmidt

Johnson

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Natural climate variation, such as that caused by volcanoes, is the basis for identifying anthropogenic climate change. However, knowledge of the history of volcanic activity is inadequate, particularly concerning the explosivity of specific events. Some material is deposited in ice cores, but the concentration of glacial sulfate does not distinguish between tropospheric and stratospheric eruptions. Stable sulfur isotope abundances contain additional information, and recent studies show a correlation between volcanic plumes that reach the stratosphere and mass-independent anomalies in sulfur isotopes in glacial sulfate. We describe a mechanism, photoexcitation of SO 2 , that links the two, yielding a useful metric of the explosivity of historic volcanic events. A plume model of S(IV) to S(VI) conversion was constructed including photochemistry, entrainment of background air, and sulfate deposition. Isotopologue-specific photoexcitation rates were calculated based on the UV absorption cross-sections of 32 SO 2 , 33 SO 2 , 34 SO 2 , and 36 SO 2 from 250 to 320 nm. The model shows that UV photoexcitation is enhanced with altitude, whereas mass-dependent oxidation, such as SO 2 + OH, is suppressed by in situ plume chemistry, allowing the production and preservation of a mass-independent sulfur isotope anomaly in the sulfate product. The model accounts for the amplitude, phases, and time development of Δ 33 S/δ 34 S and Δ 36 S/Δ 33 S found in glacial samples. We are able to identify the process controlling mass-independent sulfur isotope anomalies in the modern atmosphere. This mechanism is the basis of identifying the magnitude of historic volcanic events.A ttribution of climate change relies on our understanding of natural climate variation. Volcanoes affect climate, but it is not easy to use proxy records to derive the climate impact of a given historical eruption, primarily because we lack knowledge about the volcanoes themselves. Some so-called Plinian eruptions penetrate the stratosphere, resulting in multiyear climate impacts (1). Volcanic sulfur dioxide (SO 2 ) in a plume is photooxidized in the atmosphere. In the troposphere, the sulfuric acid product is washed out as sulfate in acid rain in a matter of weeks. A Plinian eruption, in contrast, intensifies the stratospheric sulfate aerosol (SSA) layer (2), increasing the planet's albedo (3) and enhancing midlatitude O 3 depletion (4) for more than a year. Ice core records of sulfate provide an important record of volcanic activity (5), but the concentration of sulfate alone does not indicate the explosivity of the event and specifically, if the plume penetrated the stratosphere (6).A series of groundbreaking studies has shown that sulfur isotopes in sulfate from Plinian eruptions show mass-independent fractionation (MIF) (6-8). Carbonyl sulfide (OCS) is thought to be the main source of background SSA in volcanically quiescent periods (9), and the reactions breaking down OCS, mainly photolysis, show no evidence of sulfur MIF (10-13). MIF is not seen at the sour...

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Photoabsorption cross‐section measurements of ³²S, ³³S, ³⁴S, and ³⁶S sulfur dioxide from 190 to 220 nm

et al. 2015

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) made using a dual-beam photospectrometer. The measured absorption cross sections show an apparent pressure dependence and a newly developed analytical model shows that this is caused by underresolved fine structure. The model made possible the calculation of absorption cross sections at the zero-pressure limit that can be used to calculate photolysis rates for atmospheric scenarios. The Ε isotopic fractionations of +4.6 ± 11.6‰, +8.8 ± 9.0‰, and À8.8 ± 19.6‰, respectively. From these spectra isotopic effects during photolysis in the Archean atmosphere can be calculated and compared to the Archean sedimentary record. Our results suggest that broadband solar UV photolysis is capable of producing the mass-independent fractionation observed in the Archean sedimentary record without involving shielding by specific gaseous compounds in the atmosphere including SO 2 itself. The estimated magnitude of 33 Ε, for example, is close to the maximum Δ 33 S observed in the geological record.

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High‐precision spectroscopy of ³²S, ³³S, and ³⁴S sulfur dioxide: Ultraviolet absorption cross sections and isotope effects

Cited by 110 publications

References 53 publications

Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox

Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox

SO₂photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism

Photoabsorption cross‐section measurements of ³²S, ³³S, ³⁴S, and ³⁶S sulfur dioxide from 190 to 220 nm

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High‐precision spectroscopy of 32S, 33S, and 34S sulfur dioxide: Ultraviolet absorption cross sections and isotope effects

Cited by 110 publications

References 53 publications

Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox

Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox

SO2photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism

Photoabsorption cross‐section measurements of 32S, 33S, 34S, and 36S sulfur dioxide from 190 to 220 nm

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High‐precision spectroscopy of ³²S, ³³S, and ³⁴S sulfur dioxide: Ultraviolet absorption cross sections and isotope effects

SO₂photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism

Photoabsorption cross‐section measurements of ³²S, ³³S, ³⁴S, and ³⁶S sulfur dioxide from 190 to 220 nm