24 Apr 2023
 | 24 Apr 2023
Status: this preprint is currently under review for the journal AMT.

SI-traceable validation of a balloon-borne spectrometer for water vapor measurements in the upper atmosphere

Simone Brunamonti, Manuel Graf, Tobias Bühlmann, Céline Pascale, Ivan Ilak, Lukas Emmenegger, and Béla Tuzson

Abstract. Despite its crucial role in the Earth's radiative balance, upper air water vapor (H2O) is still lacking accurate, in-situ, and continuous monitoring. Especially in the upper troposphere-lower stratosphere (UTLS), these measurements are notoriously difficult, and significant discrepancies were reported in the past between different measuring techniques. Here, we present a laboratory validation of a recently developed mid-IR quantum-cascade laser absorption spectrometer for balloon-borne measurements of H2O in the UTLS (ALBATROSS). The validation was performed using SI-traceable reference gas mixtures generated based on the permeation method and dynamic dilution. The accuracy and precision of ALBATROSS were evaluated at a wide range of pressures (30‒250 mbar) and H2O amount fractions (2.5‒35 ppm), representative of the atmospheric variability of H2O in the UTLS. Best agreement was achieved by implementing a quadratic Speed-Dependent Voigt Profile (qSDVP) line-shape model in the spectroscopic retrieval algorithm. The molecular parameters required by this parameterization were determined empirically using a multi-spectrum fitting approach over different pressure conditions. ALBATROSS achieves an accuracy better than ±1.5 % with respect to the SI-traceable reference at all investigated pressures and H2O amount fractions. The measurement precision was found to be better than 30 ppb (i.e., 0.1 % at 35 ppm H2O) at 1 s resolution for all conditions. This performance, unprecedented for a balloon-borne hygrometer, demonstrates the exceptional potential of mid-IR laser absorption spectroscopy as a new reference method for in-situ measurements of H2O in the UTLS.

Simone Brunamonti et al.

Status: open (until 16 Jun 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2023-83', Alan Fried, 20 May 2023 reply
  • RC2: 'Comment on amt-2023-83', Markus Miltner, 01 Jun 2023 reply

Simone Brunamonti et al.

Simone Brunamonti et al.


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Short summary
Despite its low concentration, water vapor in the upper atmosphere (8–25 km altitude) has a significant impact on the rate of global warming. We developed a new instrument for water vapor measurements aboard meteorological balloons based on laser absorption spectroscopy. Here, we investigate the performance of our spectrometer under laboratory conditions using high quality standard reference gases, showing unprecedented accuracy and precision for a lightweight balloon-borne instrument.