Correcting the impact of the isotope composition on the mixing ratio dependency of water vapour isotope measurements with cavity ring-down spectrometers
Recent advances in laser spectroscopy enable high-frequency in situ measurements of the isotope composition of water vapour. At low water vapour mixing ratios, however, the measured stable water isotope composition can be substantially affected by a measurement artefact known as the mixing ratio dep...
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ftcopernicus:oai:publications.copernicus.org:amt79274 2023-05-15T15:13:11+02:00 Correcting the impact of the isotope composition on the mixing ratio dependency of water vapour isotope measurements with cavity ring-down spectrometers Weng, Yongbiao Touzeau, Alexandra Sodemann, Harald 2020-06-16 application/pdf https://doi.org/10.5194/amt-13-3167-2020 https://amt.copernicus.org/articles/13/3167/2020/ eng eng doi:10.5194/amt-13-3167-2020 https://amt.copernicus.org/articles/13/3167/2020/ eISSN: 1867-8548 Text 2020 ftcopernicus https://doi.org/10.5194/amt-13-3167-2020 2020-07-20T16:22:06Z Recent advances in laser spectroscopy enable high-frequency in situ measurements of the isotope composition of water vapour. At low water vapour mixing ratios, however, the measured stable water isotope composition can be substantially affected by a measurement artefact known as the mixing ratio dependency, which is commonly considered independent of the isotope composition. Here we systematically investigate how the mixing ratio dependency, in a range from 500 to 23 000 ppmv of three commercial cavity ring-down spectrometers, is affected by the isotope composition of water vapour. We find that the isotope composition of water vapour has a substantial and systematic impact on the mixing ratio dependency for all three analysers, particularly at mixing ratios below 4000 ppmv. This isotope composition dependency can create a deviation of ±0.5 ‰ and ±6.0 ‰ for δ 18 O and δ D , respectively, at ∼2000 ppmv, resulting in about 2 ‰–3 ‰ deviation for the d -excess. An assessment of the robustness of our findings shows that the overall behaviour is reproducible over up to 2 years for different dry gas supplies, while being independent of the method for generating the water vapour and being the first order of the evaluation sequence. We propose replacing the univariate mixing ratio dependency corrections with a new, combined isotope composition–mixing ratio dependency correction. Using aircraft- and ship-based measurements in an Arctic environment, we illustrate a relevant application of the correction. Based on our findings, we suggest that the dependency on the isotope composition may be primarily related to spectroscopy. Repeatedly characterising the combined isotope composition–mixing ratio dependency of laser spectrometers when performing water vapour measurements at high elevations, on aircraft, or in polar regions appears critical to enable reliable data interpretation in dry environments. Text Arctic Copernicus Publications: E-Journals Arctic Atmospheric Measurement Techniques 13 6 3167 3190 |
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Copernicus Publications: E-Journals |
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ftcopernicus |
language |
English |
description |
Recent advances in laser spectroscopy enable high-frequency in situ measurements of the isotope composition of water vapour. At low water vapour mixing ratios, however, the measured stable water isotope composition can be substantially affected by a measurement artefact known as the mixing ratio dependency, which is commonly considered independent of the isotope composition. Here we systematically investigate how the mixing ratio dependency, in a range from 500 to 23 000 ppmv of three commercial cavity ring-down spectrometers, is affected by the isotope composition of water vapour. We find that the isotope composition of water vapour has a substantial and systematic impact on the mixing ratio dependency for all three analysers, particularly at mixing ratios below 4000 ppmv. This isotope composition dependency can create a deviation of ±0.5 ‰ and ±6.0 ‰ for δ 18 O and δ D , respectively, at ∼2000 ppmv, resulting in about 2 ‰–3 ‰ deviation for the d -excess. An assessment of the robustness of our findings shows that the overall behaviour is reproducible over up to 2 years for different dry gas supplies, while being independent of the method for generating the water vapour and being the first order of the evaluation sequence. We propose replacing the univariate mixing ratio dependency corrections with a new, combined isotope composition–mixing ratio dependency correction. Using aircraft- and ship-based measurements in an Arctic environment, we illustrate a relevant application of the correction. Based on our findings, we suggest that the dependency on the isotope composition may be primarily related to spectroscopy. Repeatedly characterising the combined isotope composition–mixing ratio dependency of laser spectrometers when performing water vapour measurements at high elevations, on aircraft, or in polar regions appears critical to enable reliable data interpretation in dry environments. |
format |
Text |
author |
Weng, Yongbiao Touzeau, Alexandra Sodemann, Harald |
spellingShingle |
Weng, Yongbiao Touzeau, Alexandra Sodemann, Harald Correcting the impact of the isotope composition on the mixing ratio dependency of water vapour isotope measurements with cavity ring-down spectrometers |
author_facet |
Weng, Yongbiao Touzeau, Alexandra Sodemann, Harald |
author_sort |
Weng, Yongbiao |
title |
Correcting the impact of the isotope composition on the mixing ratio dependency of water vapour isotope measurements with cavity ring-down spectrometers |
title_short |
Correcting the impact of the isotope composition on the mixing ratio dependency of water vapour isotope measurements with cavity ring-down spectrometers |
title_full |
Correcting the impact of the isotope composition on the mixing ratio dependency of water vapour isotope measurements with cavity ring-down spectrometers |
title_fullStr |
Correcting the impact of the isotope composition on the mixing ratio dependency of water vapour isotope measurements with cavity ring-down spectrometers |
title_full_unstemmed |
Correcting the impact of the isotope composition on the mixing ratio dependency of water vapour isotope measurements with cavity ring-down spectrometers |
title_sort |
correcting the impact of the isotope composition on the mixing ratio dependency of water vapour isotope measurements with cavity ring-down spectrometers |
publishDate |
2020 |
url |
https://doi.org/10.5194/amt-13-3167-2020 https://amt.copernicus.org/articles/13/3167/2020/ |
geographic |
Arctic |
geographic_facet |
Arctic |
genre |
Arctic |
genre_facet |
Arctic |
op_source |
eISSN: 1867-8548 |
op_relation |
doi:10.5194/amt-13-3167-2020 https://amt.copernicus.org/articles/13/3167/2020/ |
op_doi |
https://doi.org/10.5194/amt-13-3167-2020 |
container_title |
Atmospheric Measurement Techniques |
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13 |
container_issue |
6 |
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3167 |
op_container_end_page |
3190 |
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1766343776191643648 |