Japan Geoscience Union Meeting 2022

Presentation information

[J] Poster

A (Atmospheric and Hydrospheric Sciences ) » A-CC Cryospheric Sciences & Cold District Environment

[A-CC29] Ice cores and paleoenvironmental modeling

Fri. Jun 3, 2022 11:00 AM - 1:00 PM Online Poster Zoom Room (9) (Ch.09)

convener:Kenji Kawamura(National Institute of Polar Research, Research Organization of Information and Systems), convener:Nozomu Takeuchi(Chiba University), Ayako Abe-Ouchi(Atmosphere and Ocean Research Institute, The University of Tokyo), convener:Ryu Uemura(Nagoya University), Chairperson:Ryu Uemura(Nagoya University), Kenji Kawamura(National Institute of Polar Research, Research Organization of Information and Systems)

11:00 AM - 1:00 PM

[ACC29-P06] Sulfur isotope fractionation during SO2 photolysis in low-temperature and low-pressure atmospheres: Implication for sulfur chemistry during stratospheric volcanic events

*Yoshiaki Endo1, Yasuhito Sekine1,2, Yuichiro Ueno1,3 (1.Tokyo Institute of Technology, 2.Kanazawa University, 3.Japan Agency for Marine-Earth Science and Technology)

Keywords:sulfur isitopes, sulfate aerosol, stratosphere, sulfur dioxide, photochemistry, mass-independent fractionation

Signatures of mass-independent sulfur isotope fractionation (MIF-S; Δ33S = δ33S – 0.515δ34S ≠ 0) have been observed in stratospheric sulfate aerosols deposited in polar ice. The anomalous isotope signatures are believed to originate from photochemical reactions and to be a tracer of past stratospheric eruptions [1]. However, the origin of the isotope signatures is still debated. In the present study, we first report sulfur isotope fractionations during SO2 photolysis, including isotopic self-shielding, at both low temperatures, down to 228 K, and low pressures below 10 kPa, where pressure broadening of SO2 becomes negligible. These experimental conditions should be closer to those of the stratosphere where SO2 photolysis occurs than previous experiments performed by Whitehill et al. (2015) [2] and Endo et al. (2019) [3]. The results show that magnitude of δ34S, Δ33S, and Δ36S values become larger at lower temperatures, with the values at 228 K being ~4 times those at 296 K, whereas Δ33S/δ34S and Δ36S/Δ33S ratios depend little on temperature (~ +0.12 and ~ –3.1, respectively). We found that the two-component mixing of SO2 oxidation by OH and SO2 photolysis in the stratosphere can reproduce δ34S and Δ33S of the modern SSA when the contribution ratio of SO2 photolysis to SO3 production is ~20%. The contribution ratio is consistent with photochemical model results of Whitehill et al. (2015) [2]. Thus, we suggest that the MIF-S signatures in stratospheric sulfate aerosols originate from SO2 photolysis. Our results are the basis of interpreting the MIF-S signatures and understanding sulfur chemistry during large volcanic events.
[1] Savarino et al. (2003). Geophys. Res. Lett., 30(21), 9−12.
[2] Whitehill et al. (2015). Atmos. Chem. Phys., 15(4), 1843−1864.
[3] Endo et al. (2019). Geophys. Res. Lett., 46(1), 483−491.