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Volume 17, issue 2
Atmos. Chem. Phys., 17, 1271-1295, 2017
https://doi.org/10.5194/acp-17-1271-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 17, 1271-1295, 2017
https://doi.org/10.5194/acp-17-1271-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 27 Jan 2017

Research article | 27 Jan 2017

Detection of water vapour absorption around 363 nm in measured atmospheric absorption spectra and its effect on DOAS evaluations

Johannes Lampel1,a, Denis Pöhler2, Oleg L. Polyansky3,4, Aleksandra A. Kyuberis4, Nikolai F. Zobov4, Jonathan Tennyson3, Lorenzo Lodi3, Udo Frieß2, Yang Wang1, Steffen Beirle1, Ulrich Platt2, and Thomas Wagner1 Johannes Lampel et al.
  • 1Max Planck Institute for Chemistry, 55128 Mainz, Germany
  • 2Institute of Environmental Physics, University of Heidelberg, 69120 Heidelberg, Germany
  • 3Department of Physics and Astronomy, University College London, Gower St, London WC1E 6BT, UK
  • 4Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia
  • anow at: Institute of Environmental Physics, University of Heidelberg, 69120 Heidelberg, Germany

Abstract. Water vapour is known to absorb radiation from the microwave region to the blue part of the visible spectrum with decreasing efficiency. Ab initio approaches to model individual absorption lines of the gaseous water molecule predict absorption lines up to its dissociation limit at 243 nm.

We present the first evidence of water vapour absorption near 363 nm from field measurements using data from multi-axis differential optical absorption spectroscopy (MAX-DOAS) and long-path (LP)-DOAS measurements. The identification of the absorptions was based on the recent POKAZATEL line list by Polyansky et al. (2017).

For MAX-DOAS measurements, we observed absorption by water vapour in an absorption band around 363 nm with optical depths of up to 2 × 10−3. The retrieved column densities from 2 months of measurement data and more than 2000 individual observations at different latitudes correlate well with simultaneously measured well-established water vapour absorptions in the blue spectral range from 452 to 499 nm (R2 = 0.89), but the line intensities at around 363 nm are underestimated by a factor of 2.6  ±  0.5 by the ab initio model. At a spectral resolution of 0.5 nm, we derive a maximum cross section value of 2.7 × 10−27 cm2 molec−1 at 362.3 nm. The results were independent of the used literature absorption cross section of the O4 absorption, which overlays this water vapour absorption band.

Also water vapour absorption around 376 nm was identified. Below 360 nm no water vapour absorption above 1.4 × 10−26 cm2 molec−1 was observed.

The newly found absorption can have a significant impact on the spectral retrievals of absorbing trace-gas species in the spectral range around 363 nm. Its effect on the spectral analysis of O4, HONO and OClO is discussed.

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Short summary
Water vapour is known to absorb radiation from the microwave region to the blue part of the visible spectrum. Ab initio approaches to model individual absorption lines of the gaseous water molecule predict absorption lines until its dissociation limit at 243 nm. We present first evidence of water vapour absorption near 363 nm from field measurements using data from multi-axis differential optical absorption spectroscopy (MAX-DOAS) and long-path (LP)-DOAS measurements.
Water vapour is known to absorb radiation from the microwave region to the blue part of the...
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