the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Cavity ring-down spectroscopy of water vapor in the near-UV region
- 1Department of Chemical Physics, University of Science and Technology of China, Hefei, 230026 China
- 2Center for Astrophysics, Harvard and Smithsonian, Atomic and Molecular Physics Division, Cambridge, MA, 02138 USA
- 3Kostas Research Institute for Homeland Security, Burlington, MA, 01803 USA
- 1Department of Chemical Physics, University of Science and Technology of China, Hefei, 230026 China
- 2Center for Astrophysics, Harvard and Smithsonian, Atomic and Molecular Physics Division, Cambridge, MA, 02138 USA
- 3Kostas Research Institute for Homeland Security, Burlington, MA, 01803 USA
Abstract. Water vapor absorption in the near-ultraviolet region is essential to describe the energy budget of Earth, but little spectroscopic information is available since it is a challenging spectral region for both experimental and theoretical studies. A continuous-wave cavity ring-down spectroscopic experiment was built to record absorption lines of water vapor around 415 nm. With a minimum detectable absorption coefficient of 4 × 10−10 cm−1, 40 rovibrational transitions of H162O were observed in this work, and 27 of them were assigned to the (224), (205), (710), (304), (093), (125), and (531) vibrational bands. A comparison of line positions and intensities determined in this work to the most recent HITRAN database is presented. Water vapor absorption cross-sections near 415 nm were calculated based on our measurements, which vary between 1 × 10−26 and 5 × 10−26 cm2/molecule. These data will also significantly impact the spectroscopy detection of trace gas species in the near-UV region.
Qing-Ying Yang et al.
Status: open (until 19 Jul 2022)
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RC1: 'Comment on amt-2022-139', Anonymous Referee #1, 21 Jun 2022
reply
The manuscript "Cavity ring-down spectroscopy of water vapor in the near-UV region" is well written and structured and adresses the important question of water vapour absorption in the near-UV region from about 33000-24000 cm-1 or 300-420nm. These absorption are typically not used to obtain water vapour concentrations in the atmosphere or in experiments, but may overlay other absorbers and thus introduce systematic biases in measurements of various trace gases as mentioned in the manuscript. Water vapour is not the only absorber where work needs to be done for further advances in remote sensing applications, but often one of the strongest interferences in the near UV region. For other gases important progress was reported e.g. in Finkenzeller and Volkamer 2022 in the same spectral range.
Only a few comments follow:
Figure 5: The line colour might be chosen differently to distinguish the upper limits by Wilson et al and Lampel et al better. Lampel et al 2017 reported the upper limit only up to 350nm, this is wrong in the plot. The same publication also estimated the actual absorption cross-section around 363nm at a lower spectral resolution, which might also be included in the plot. The reported discreapancy there between observations and POKAZATEL was explained later in Conway et al 2020.Lampel et al 2015 estimated scaling factors for older HITRAN versions also for the spectral range around 400 and 415nm, but this might be difficult to include in the figure, and no dominating scaling factor for individual water vapour absorption lines listed in Table 1 between modelled and measured intensities can be seen.
Maybe also Conway et al 2020 or a recent line list could be included in the plot, as HITRAN based absorption cross sections were underestimating the actual absorptions especially in the UV due to a relatively large line-cutoff value.
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Henning Finkenzeller, Rainer Volkamer,O2–O2 CIA in the gas phase: Cross-section of weak bands, and continuum absorption between 297–500 nm,Journal of Quantitative Spectroscopy and Radiative Transfer,Volume 279,2022,108063,ISSN 0022-4073,https://doi.org/10.1016/j.jqsrt.2021.108063.
Qing-Ying Yang et al.
Qing-Ying Yang et al.
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