Large Mass Independent Sulfur Isotope Fractionations during the Photopolymerization of 12CS2 and 13CS2

Zmolek, Peter B.; Xu, Xianping; Jackson, Teresa L.; Thiemens, M. H.; Trogler, William C.

doi:10.1021/jp9907140

Cited by 52 publications

(56 citation statements)

References 47 publications

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“…In particular, pairs of levels capable of interacting with each other and that are near-degenerate for one isotopologue may be nondegenerate for other isotopologues. These effects were cited previously as a source of S-MIF during the photopolymerization of CS 2 (41,42) and oxygen MIF during the photodissociation of CO 2 (43) and CO (44). In these three cases, the anomalous isotope effects have been attributed to differences in intersystem crossing (ISC) rates from an initially excited singlet state to a reactive (or dissociative) triplet state.…”

Section: Results Of Photochemical Experimentsmentioning

confidence: 82%

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO₂and the implications to the early earth’s atmosphere

Whitehill

Xie

et al. 2013

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

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Signatures of mass-independent isotope fractionation (MIF) † Significant deviations from these mass-dependent scaling laws are referred to as mass-independent fractionation (MIF), and serve as important tracers in the earth and planetary sciences (see refs. 3-5).Early studies suggested that MIF could result only from nucleosynthetic processes (6), and the earliest measurements of oxygen MIF in calcium-aluminum inclusions of meteorites originally were interpreted to be nucleosynthetic in origin (7). It eventually was suggested (8) that chemical processes, such as tunneling or processes associated with predissociation, also might produce MIF. The first experimental evidence for a chemical origin of MIF came from ozone generated by an electric discharge or UV radiation (9, 10). The discovery of oxygen MIF in stratospheric ozone (11) soon triggered intense research into the physiochemical origin of MIF in the ozone system (see refs. 12-14). The possible chemical origins of MIF signatures still are poorly understood.For the sulfur isotope system ( 32 S, 33 S, 34 S, and 36 S), Farquhar et al. (15) made the remarkable discovery that mass-independent sulfur isotope fractionation (S-MIF) is prevalent in sedimentary rocks older than ca. 2.4 Ga but absent in rocks from subsequent periods. The disappearance of S-MIF at about 2.4 Ga (16, 17) signifies a fundamental change in the earth's surface sulfur cycles, and generally is linked to the suppression of both SO 2 photolysis and the formation of elemental sulfur aerosols by the rise of atmospheric oxygen levels (15,18,19). The Archean S-MIF is considered the most compelling evidence for an anoxic early atmosphere and constrains Archean oxygen levels to be less than 10−5 of present levels (19). This model of oxygen evolution, however, depends critically on the assumption that UV photolysis of SO 2 by ∼200 nm radiation is the ultimate source of the anomalous sulfur isotope signature (18). Constraining the source of the S-MIF requires a thorough understanding of the physiochemical origins of S-MIF during the photochemistry of SO 2 .SO 2 exhibits two strong absorption band systems in the UV region: one between 185 nm and 235 nm (C 1 B 2 ←X

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Section: Results Of Photochemical Experimentsmentioning

confidence: 82%

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO₂and the implications to the early earth’s atmosphere

Whitehill

Xie

et al. 2013

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

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“…states of different isotopomers [e.g., Zmolek et al, 1999;Romero and Thiemens, 2003]. Of these, the surface reaction model of Lasaga et al [2008] and the well-established MIE [Buchachenko, 2000] are the only reactions that would apply to heterogeneous reactions (MIE also to gas phase), but we suggest that it is possible to rule these out as viable candidates for our observations.…”

Section: Mechanisms For Producing Mass-independent Sulfur Isotope Anomentioning

confidence: 83%

“…[33] Research done to date has been largely exploratory and includes studies of photolysis of SO 2 and H 2 S [Farquhar et al, 2000b[Farquhar et al, , 2001] and photopolymerization of CS and CS 2 [Colman et al, 1996;Zmolek et al, 1999] Romero and Thiemens, 2003;Savarino et al, 2003;Baroni et al, 2007] and the requirement of short wavelengths has cited the reactions that produce the effects in the stratosphere. Note that the reactions that produce the effect may be related to sulfur dioxide, or they may be related to photolysis of long-lived bound states (or intermediates) [Farquhar et al, 2001;Lyons, 2008].…”

Section: Mechanisms For Producing Mass-independent Sulfur Isotope Anomentioning

confidence: 99%

Identification of sources and formation processes of atmospheric sulfate by sulfur isotope and scanning electron microscope measurements

et al. 2010

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[1] Atmospheric sulfate aerosols have a cooling effect on the Earth's surface and can change cloud microphysics and precipitation. China has heavy loading of sulfate, but their sources and formation processes remain uncertain. In this study we characterize possible sources and formation processes of atmospheric sulfate by analyzing sulfur isotope abundances ( 32 S, 33 S, 34 S, and 36 S) and by detailed X-ray diffraction and scanning electron microscope (SEM) imaging of aerosol samples acquired at a rural site in northern China from March to August 2005. The comparison of SEM images from coal fly ash and the atmospheric aerosols suggests that direct emission from coal combustion is a substantial source of primary atmospheric sulfate in the form of CaSO 4 . Airborne gypsum (CaSO 4 ·2H 2 O) is usually attributed to eolian dust or atmospheric reactions with H 2 SO 4 . SEM imaging also reveals mineral particles with soot aggregates adhered to the surface where they could decrease the single scattering albedo of these aerosols. In summer months, heterogeneous oxidation of SO 2 , derived from coal combustion, appears to be the dominant source of atmospheric sulfate. Our analyses of aerosol sulfate show a seasonal variation in D 33 S (D 33 S describes either a 33 S excess or depletion relative to that predicted from consideration of classical mass-dependent isotope effects). Similar sulfur isotope variations have been observed in other atmospheric samples and in (homogenous) gas-phase reactions. On the basis of atmospheric sounding and satellite data as well as a possible relationship between D 33 S and Convective Available Potential Energy (CAPE) during the sampling period, we attribute the sulfur isotope anomalies (D 33 S and D 36 S) in Xianghe aerosol sulfates to another atmospheric source (upper troposphere or lower stratosphere).Citation: Guo, Z., Z. Li, J. Farquhar, A. J. Kaufman, N. Wu, C. Li, R. R. Dickerson, and P. Wang (2010), Identification of sources and formation processes of atmospheric sulfate by sulfur isotope and scanning electron microscope measurements,

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“…Physical mechanisms included entrainment of background air, modeled as eddy diffusion mixing using constants taken from the literature (40), and settling of sulfate, where the bin time constant was chosen to correspond to physical parameters. Four stable isotopes of sulfur, 32 S, 33 S, 34 S, and 36 S, were explicitly considered in the model. Model scenarios were run at altitudes of 20, 26, and 32 km to indicate the effect of varying actinic flux, pressure, and temperature on the model output.…”

Section: Methodsmentioning

confidence: 99%

“…Finally, a δ 34 S value for volcanic SO 2 of 4.7‰ is defined based on the volcanic sulfur average (41), but note that initial sulfur isotopic composition in 34 S is also the parameter that determines δ 34 S values in produced sulfate as described in SI Materials and Methods.…”

Section: Methodsmentioning

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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Large Mass Independent Sulfur Isotope Fractionations during the Photopolymerization of ¹²CS₂ and ¹³CS₂

Cited by 52 publications

References 47 publications

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO₂and the implications to the early earth’s atmosphere

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO₂and the implications to the early earth’s atmosphere

Identification of sources and formation processes of atmospheric sulfate by sulfur isotope and scanning electron microscope measurements

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

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Large Mass Independent Sulfur Isotope Fractionations during the Photopolymerization of 12CS2 and 13CS2

Cited by 52 publications

References 47 publications

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO2and the implications to the early earth’s atmosphere

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO2and the implications to the early earth’s atmosphere

Identification of sources and formation processes of atmospheric sulfate by sulfur isotope and scanning electron microscope measurements

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

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Large Mass Independent Sulfur Isotope Fractionations during the Photopolymerization of ¹²CS₂ and ¹³CS₂

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO₂and the implications to the early earth’s atmosphere

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO₂and the implications to the early earth’s atmosphere

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