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Abstract 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 SO 2 photolysis. Isotopic self‐shielding is known to produce S‐MIF, which could be changed by both the partial pressure of SO 2 ( p SO 2 ) and by the total pressure ( p Total). Our experimental results show that both Δ 33 S and Δ 36 S values are constant when total pressure is below 10 kPa at constant p SO 2 , whereas they decrease as total pressure increases. The result suggests that pressure broadening of the SO 2 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 p SO 2 and p Total. Consequently, we conclude that the Archean Δ 33 S and Δ 36 S correlation can only be achieved when the total pressure of the Archean atmosphere was below 100 kPa, or it was produced in the upper atmosphere.
Endo et al. (Thu,) studied this question.