11:45 AM - 12:00 PM
[ACC33-11] A measurement system for triple oxygen isotopic compositions of hydrogen peroxide (Δ17O(H2O2)) with reduced sample size applicable to ice core analysis
Keywords:Triple oxygen isotopic compositions (Δ17O), Hydrogen peroxide (H2O2), Ice core
Triple oxygen isotopic compositions (Δ17O ≒ δ17O - 0.52 × δ18O) of oxyanions, such as nitrate and sulfate, vary depending on the relative contribution of different oxidants, including O3 (Δ17O ≈ 39‰) and OH radicals (Δ17O ≈ 0‰), during their formation processes in the atmosphere. Therefore, these signatures preserved in ice cores have been considered as potential proxies for reconstructing the past atmospheric oxidants (Alexander and Mickley, 2015). However, these signatures are sensitive to not only the oxidant concentrations but other processes such as post-depositional recycling between snow and atmosphere (Jiang et al., 2021) or in-cloud oxidation pathways depending on pH (Hattori et al., 2021), requiring the development of other proxies.
The Δ17O value of hydrogen peroxide (H2O2) is one of the potential proxies for the past atmospheric oxidants. There exists only one set of measurements of Δ17O(H2O2) in rainwater at the coast of California, showing that the value varies from 0.9 to 2.4‰ (Savarino and Thiemens, 1999). However, a large sample volume of ~4 L had hampered its application to ice core samples and even further analyses of rainwater samples. Consequently, the controlling factors of the proxy remain to be explored.
In this study, we developed a new measurement method for Δ17O(H2O2) values with a small sample volume that is applicable to ice cores. H2O2 is converted to O2 molecules by reaction with potassium permanganate (KMnO4) and then introduced into an isotope ratio mass spectrometer (IRMS) using a continuous flow system, in contrast to the previous work using a dual inlet system which requires a large sample volume (Savarino and Thiemens, 1999; Guo et al., 2022). The O2 blanks from the room air and dissolved O2 in sample liquids were removed by purging the system with the pure helium and reduced to ~10 nmol in total. This enables us to measure Δ17O(H2O2) with a few 100s mL of samples in cases of typical rainwater and ice cores (e.g. Kok, 1985; Kawakami et al., 2023), within the precision of 0.1‰. We further confirmed that Δ17O(H2O2) values of commercial H2O2 reagents measured by our system show consistent values with those measured by the traditional dual inlet system (Guo et al., 2022). In the presentation, we report the first result of Δ17O(H2O2) values in precipitation and snow samples collected in the middle North region of Japan and discuss the possible factors controlling the proxy.
The Δ17O value of hydrogen peroxide (H2O2) is one of the potential proxies for the past atmospheric oxidants. There exists only one set of measurements of Δ17O(H2O2) in rainwater at the coast of California, showing that the value varies from 0.9 to 2.4‰ (Savarino and Thiemens, 1999). However, a large sample volume of ~4 L had hampered its application to ice core samples and even further analyses of rainwater samples. Consequently, the controlling factors of the proxy remain to be explored.
In this study, we developed a new measurement method for Δ17O(H2O2) values with a small sample volume that is applicable to ice cores. H2O2 is converted to O2 molecules by reaction with potassium permanganate (KMnO4) and then introduced into an isotope ratio mass spectrometer (IRMS) using a continuous flow system, in contrast to the previous work using a dual inlet system which requires a large sample volume (Savarino and Thiemens, 1999; Guo et al., 2022). The O2 blanks from the room air and dissolved O2 in sample liquids were removed by purging the system with the pure helium and reduced to ~10 nmol in total. This enables us to measure Δ17O(H2O2) with a few 100s mL of samples in cases of typical rainwater and ice cores (e.g. Kok, 1985; Kawakami et al., 2023), within the precision of 0.1‰. We further confirmed that Δ17O(H2O2) values of commercial H2O2 reagents measured by our system show consistent values with those measured by the traditional dual inlet system (Guo et al., 2022). In the presentation, we report the first result of Δ17O(H2O2) values in precipitation and snow samples collected in the middle North region of Japan and discuss the possible factors controlling the proxy.