Presentation Information
[AAS08-P47]Factors controlling the variability in Δ17O values of hydrogen peroxide in precipitatio
*Rintaro Hamamoto1, Sakiko Ishino1, Harumichi Shitamori1, Yoshinori Iizuka2, Sumito Matoba2, Hao Guo3, Mang Lin3, Koichi Watanabe4, Joel Savarino5, Shohei Hattori6 (1.Kanazawa University, 2.Institute of Low Temperature Science, Hokkaido University, 3.Guangzhou Institute of Geochemistry, CAS, 4.Toyama Prefectural University, 5.Univ. Grenoble Alpes, CNRS, IRD, G-INP, IGE, 6.International Center for Isotope Effects Research, Nanjing University)
Keywords:
Triple Oxygen Isoptopic Composition,Ozone,Hydrogen Peroxide,Precipitaion
Tropospheric ozone (O3) is not only a major component of photochemical smog, causing respiratory diseases and damaging plants and crops, but also the third most important greenhouse gas after CO2 and methane. Consequently, it is a key target for mitigation in air quality management. However, our understanding of the increase in tropospheric O3 since the pre-industrial time (1850) to the present and the factors driving its variability remain limited. Direct observational data for tropospheric O3 are available only since 1956 (Cooper et al., 2014). Moreover, because O3 rapidly decomposes after deposition to the surface, it is not preserved in paleoclimate archives such as ice cores. Research has therefore focused on exploring alternative proxies, such as isotope ratios of impurities in ice cores, that might retain information on past O3 levels (Alexander and Mickley, 2015).
To address this challenge, we focus on a novel proxy: the triple oxygen isotope composition (Δ17O = δ17O - 0.52 × δ18O) of hydrogen peroxide (H2O2). Specifically high Δ17O value in O3 (≃ 39 ‰), in contrast to other oxygen species in the atmosphere (e.g., OH and O2, Δ17O ≃ 0 ‰), is partially inherited to H2O2 through its formation processes. Consequently, Δ17O(H2O2) is expected to vary depending on the relative contributions of O3-involved reactions and other pathways. The existing measurements of Δ17O(H2O2) in precipitation samples collected in La Jolla, California, reported values ranging from 1.3 to 2.4 ‰ (Savarino and Thiemens, 1999); however, its relationship with ambient O3 concentrations has not been examined. Moreover, the requirement of large sample volume (4 L) for analysis posed a major limitation, having hampered the Δ17O(H2O2) measurements of natural precipitation samples ever since.
In this study, we have developed a new analytical method for Δ17O(H2O2) using a continuous flow GC-IRMS system, successfully reducing the required sample volume to 200 mL. With this new method, we conducted an extended measurements of Δ17O(H2O2) in precipitation collected at Kanazawa (36.5°N, 136.7°E), from March through November 2025, to examine the relationship with O3 concentration. Δ17O(H2O2) values varied between 1.1 and 2.5 ‰ (n = 30), which was broadly consistent with that reported in previous study at California. Importantly, the observed Δ17O(H2O2) values were not correlated with O3 concentrations in Kanazawa (p = 0.40). However, during the chemical conversion process of H2O2 in the samples to O2 gas within the measurement, we observed an excessive amount (>120%) of O2 was produced for most cases (n = 20). This phenomena suggest a significant interference of the analysis by H2O2 or O2 generated from sources other than the original H2O2 in precipitation. In this presentation, we discuss the sources of this interference and the potential approches to avoid them.
To address this challenge, we focus on a novel proxy: the triple oxygen isotope composition (Δ17O = δ17O - 0.52 × δ18O) of hydrogen peroxide (H2O2). Specifically high Δ17O value in O3 (≃ 39 ‰), in contrast to other oxygen species in the atmosphere (e.g., OH and O2, Δ17O ≃ 0 ‰), is partially inherited to H2O2 through its formation processes. Consequently, Δ17O(H2O2) is expected to vary depending on the relative contributions of O3-involved reactions and other pathways. The existing measurements of Δ17O(H2O2) in precipitation samples collected in La Jolla, California, reported values ranging from 1.3 to 2.4 ‰ (Savarino and Thiemens, 1999); however, its relationship with ambient O3 concentrations has not been examined. Moreover, the requirement of large sample volume (4 L) for analysis posed a major limitation, having hampered the Δ17O(H2O2) measurements of natural precipitation samples ever since.
In this study, we have developed a new analytical method for Δ17O(H2O2) using a continuous flow GC-IRMS system, successfully reducing the required sample volume to 200 mL. With this new method, we conducted an extended measurements of Δ17O(H2O2) in precipitation collected at Kanazawa (36.5°N, 136.7°E), from March through November 2025, to examine the relationship with O3 concentration. Δ17O(H2O2) values varied between 1.1 and 2.5 ‰ (n = 30), which was broadly consistent with that reported in previous study at California. Importantly, the observed Δ17O(H2O2) values were not correlated with O3 concentrations in Kanazawa (p = 0.40). However, during the chemical conversion process of H2O2 in the samples to O2 gas within the measurement, we observed an excessive amount (>120%) of O2 was produced for most cases (n = 20). This phenomena suggest a significant interference of the analysis by H2O2 or O2 generated from sources other than the original H2O2 in precipitation. In this presentation, we discuss the sources of this interference and the potential approches to avoid them.