Preprints
https://doi.org/10.5194/egusphere-2025-2916
https://doi.org/10.5194/egusphere-2025-2916
01 Jul 2025
 | 01 Jul 2025
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Kinetic fractionation of noble gases in the stratosphere over Japan

Satoshi Sugawara, Ikumi Oyabu, Kenji Kawamura, Shigeyuki Ishidoya, Shinji Morimoto, Shuji Aoki, Takakiyo Nakazawa, Sakae Toyoda, and Hideyuki Honda

Abstract. Gravitational separation of gas species in the stratosphere is caused mainly by molecular diffusion and is a powerful tool to diagnose stratospheric transport processes. Previous studies have shown that isotopic and elemental ratios of major atmospheric components decrease with increasing altitude in proportion to the differences of their mass numbers. However, there have been no reports of the vertical changes of Kr, Xe, and Ne in the stratosphere. Here we report the results of the first study of the vertical changes of Kr, Xe, and Ne in the stratosphere based on high-precision analyses. Our goal was to reveal the vertical distributions of noble gases and to clarify the mechanisms governing their separations. Noble gases were measured for the stratospheric air collected by balloon-borne cryogenic air samplers over Japan. We found that the isotopic and elemental ratios of all noble gases decreased and increased with increasing altitude for heavy and light noble gases, respectively. Vertical distributions normalized for the mass number differences indicated that the larger the mass number, the smaller the separation of both the isotopic and elemental ratios. The implication was that kinetic fractionation occurred in the stratosphere because of the differences of molecular diffusivities. We performed model simulations and were able to reproduce the kinetic fractionations for heavier noble gases. Results of model simulations suggested that the kinetic fractionations of noble gases were usable as a new tool to diagnose stratospheric transport processes.

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Satoshi Sugawara, Ikumi Oyabu, Kenji Kawamura, Shigeyuki Ishidoya, Shinji Morimoto, Shuji Aoki, Takakiyo Nakazawa, Sakae Toyoda, and Hideyuki Honda

Status: open (until 12 Aug 2025)

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Satoshi Sugawara, Ikumi Oyabu, Kenji Kawamura, Shigeyuki Ishidoya, Shinji Morimoto, Shuji Aoki, Takakiyo Nakazawa, Sakae Toyoda, and Hideyuki Honda
Satoshi Sugawara, Ikumi Oyabu, Kenji Kawamura, Shigeyuki Ishidoya, Shinji Morimoto, Shuji Aoki, Takakiyo Nakazawa, Sakae Toyoda, and Hideyuki Honda

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Short summary
Stratospheric air samples have been collected using balloon-borne cryogenic samplers over Japan and analyzed for the isotopic and elemental ratios of noble gases. We report the results of the first study on the vertical changes of Kr, Xe, and Ne in the stratosphere. The observed results suggest that not only gravitational separation but also kinetic fractionation occurred in the stratosphere. The kinetic fractionations would be an additional tool to diagnose stratospheric transport processes.
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