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

Abstract

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.

Open-path dual-comb spectroscopy of methane and VOC emissions from an unconventional oil well development in Northern Colorado

“…This was improved at the later stages of the deployment. In addition, recent work in our group has demonstrated substantially greater up-time with a similar mid-IR DCS system by minimizing thermal drifts and optical misalignment, as well as by incorporating a slow feedback to optimize spectral power during observations (Herman et al, 2023), which will enable continuous monitoring in the future.…”

“…In addition to the fit species, other molecules are present in the data but not analyzed here. HDO and HCHO can be observed in the region closer to 3.6 μm (Herman et al, 2023). The C-H stretches of heavier alkanes such as butanes can be observed, especially in time periods with large methane enhancements, but spectral interference and the lack of distinct spectral features in these gasses made the retrieval sensitivity insufficient for most of the time periods.…”

Apportionment and Inventory Optimization of Agriculture and Energy Sector Methane Emissions using Multi-month Trace Gas Measurements in Northern Colorado

“…The MIR-DCS system is similar to previously reported designs (Giorgetta et al, 2021;Ycas et al, 2019Ycas et al, , 2020 and is described in more detail in another publication (D. Herman et al, 2023).…”