31 Jan 2023
 | 31 Jan 2023

Open-path measurement of stable water isotopologues using mid-infrared dual-comb spectroscopy

Daniel I. Herman, Griffin Mead, Fabrizio R. Giorgetta, Esther Baumann, Nathan Malarich, Brian R. Washburn, Nathan R. Newbury, Ian Coddington, and Kevin C. Cossel

Abstract. We present an open-path mid-infrared dual-comb spectrometer (DCS) capable of precise measurement of the stable water isotopologues H216O and HD16O. This system ran in a remote configuration at a rural test site for 3.75 months with 60 % uptime and achieved a precision of <2 ‰ on the normalized ratio of H216O and HD16O (δD) in 1000 seconds. Here, we compare the δD values from the DCS to those from the National Ecological Observatory Network (NEON) isotopologue point sensor network. Over the multi-month campaign, the mean difference between the DCS δD values and the NEON δD values from a similar ecosystem is <2 ‰ with a standard deviation of 18 ‰, which demonstrates the inherent accuracy of DCS measurements over a variety of atmospheric conditions. We observe time-varying diurnal profiles and seasonal trends that are mostly correlated between the sites on daily time scales. This observation motivates the development of denser ecological monitoring networks aimed at understanding regional and synoptic scale water transport. Precise and accurate open-path measurements using DCS provide new capabilities for such networks.

Daniel I. Herman et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1263', Anonymous Referee #2, 16 Feb 2023
  • RC2: 'Comment on egusphere-2022-1263', Ivan Prokhorov, 20 Feb 2023

Daniel I. Herman et al.

Daniel I. Herman et al.


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Short summary
Measurements of the isotope ratio of water vapor provide information about the sources and history of water vapor at a given location, which can be used to understand the impacts of climate change on global water use. Here, we demonstrate a new method for measuring isotope ratios over long open-air paths, which can reduce sampling bias and provide more spatial averaging than standard point sensor methods. We show that this new technique has high sensitivity and accuracy.