Total Pressure Dependence of Sulfur Mass-Independent Fractionation by SO2 Photolysis
Total Pressure Dependence of Sulfur Mass-Independent Fractionation by SO2 Photolysis
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DOI：
10.1029/2018gl080730
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发表时间：
2019-01-16
影响因子：
5.2
通讯作者：
Ueno, Yuichiro
中科院分区：
文献类型：
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作者：
Endo, Yoshiaki;Danielache, Sebastian O.;Ueno, Yuichiro
硫质量独立分馏(S-MIF)可能为理解地球早期大气提供线索。我们研究了SO2光解产生的S分子荧光的总压依赖性。同位素自屏蔽效应可以产生S效应，这种效应既可以受SO2分压(pSO(2))的影响，也可以受总压(PTotal)的影响。我们的实验结果表明，在PSO(2)不变的情况下，当总压低于10kPa时，S-33和S-36的值都是恒定的，而随着总压的增加，它们都减小了。结果表明，SO2吸收谱线的压力展宽是产生S-MIF的原因。模拟的高分辨率同位素截面可以再现我们的实验结果及其随PSO(2)和pTotal的变化。因此，我们得出结论：太古宙S-33和S-36的对比只有在太古宙大气总压低于100kPa时才能实现，或者是在高层大气中产生的。太古宙沉积岩中硫的质量独立分馏(S-MIF)有助于约束地球早期大气的化学和物理状态。众所周知，二氧化硫光解会产生大量的MIF。然而，实验结果还没有模拟S分子荧光在SO2光解中观察到的机理。我们通过SO2光解研究了S分子荧光的总压效应，并成功地模拟了观测到的S分子荧光及其与总压的关系。与地质记录对比，太古宙S-MIF只有在总压低于100kPa时才能获得大的MIF，这表明太古宙大气不比现代大气厚，或S-MIF产生的光解主要发生在高海拔地区。
Sulfur Mass-Independent Fractionation (S-MIF) may provide a clue to understanding Earth's early atmosphere. We examined total pressure dependence of the S-MIF produced by SO2 photolysis. Isotopic self-shielding is known to produce S-MIF, which could be changed by both the partial pressure of SO2 (pSO(2)) and by the total pressure (pTotal). Our experimental results show that both S-33 and S-36 values are constant when total pressure is below 10kPa at constant pSO(2), whereas they decrease as total pressure increases. The result suggests that pressure broadening of the SO2 absorption line is responsible for the S-MIF. The modeled high-resolution isotopologue cross sections can reproduce our experimental results and its changes depending on both pSO(2) and pTotal. Consequently, we conclude that the Archean S-33 and S-36 correlation can only be achieved when the total pressure of the Archean atmosphere was below 100kPa, or it was produced in the upper atmosphere.Plain Language Summary Sulfur Mass-Independent Fractionation (S-MIF) in Archean sedimentary rocks could be useful to constrain the chemical and physical states of Earth's early atmosphere. SO2 photolysis is known to produce large MIF. However, experimental results have yet to model the observed mechanisms of S-MIF in SO2 photolysis. We examined the total pressure effect of S-MIF by SO2 photolysis and succeeded in modeling the observed S-MIF and its total pressure dependence. Comparing the results of this study with geological records, large Archean S-MIF could only be achieved when total pressure is below 100kPa, suggesting that the Archean atmosphere was not thicker than the modern atmosphere or that the S-MIF-yielding photolysis occurred mainly at a high altitude.