SI-traceable validation of a laser spectrometer for balloon-borne measurements of water vapor in the upper atmosphere
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Published:2023-10-06
Issue:19
Volume:16
Page:4391-4407
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ISSN:1867-8548
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Container-title:Atmospheric Measurement Techniques
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language:en
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Short-container-title:Atmos. Meas. Tech.
Author:
Brunamonti SimoneORCID, Graf Manuel, Bühlmann Tobias, Pascale CélineORCID, Ilak Ivan, Emmenegger LukasORCID, Tuzson BélaORCID
Abstract
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 have been reported in the past between different
measuring techniques. Here, we present a laboratory assessment of a recently developed mid-IR quantum-cascade laser absorption spectrometer, called ALBATROSS, for
balloon-borne measurements of H2O in the UTLS. 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 in H2O in the UTLS. The 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. In the laboratory environment, 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.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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