Assessment of laboratory O<sub>4</sub> (O<sub>2</sub>–O<sub>2</sub> collision-induced) absorption cross-sections at 360 nm using atmospheric long-path DOAS observations
<p>Absorption of light in the atmosphere by collision-induced absorption (CIA) by two oxygen molecules O<span class="inline-formula"><sub>2</sub></span>–O<span class="inline-formula"><sub>2</sub></span>, in the following refer...
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| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-07-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/18/3393/2025/amt-18-3393-2025.pdf |
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| Summary: | <p>Absorption of light in the atmosphere by collision-induced absorption (CIA) by two oxygen molecules O<span class="inline-formula"><sub>2</sub></span>–O<span class="inline-formula"><sub>2</sub></span>, in the following referred to as O<span class="inline-formula"><sub>4</sub></span>, can be used to derive properties of aerosols and clouds from remote sensing observations. In recent years, inconsistencies between the measured atmospheric O<span class="inline-formula"><sub>4</sub></span> absorption and radiative transfer simulations were found for Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements. In the presented study, over two years of observations from a long-path (LP-) DOAS instrument deployed at the German research station Neumayer, Antarctica, are analysed. While MAX-DOAS instruments measure spectra of scattered sunlight at different elevation angles, LP-DOAS utilises an artificial light source and the atmospheric absorptions are measured along a fixed (and well-defined) light path close to the surface. Further, the pristine measurement location allows one to investigate the relation between measured and modelled O<span class="inline-formula"><sub>4</sub></span> absorption over a large range of temperatures (<span class="inline-formula">−45</span> to +5 °C). Overall good agreement is found between the retrieved O<span class="inline-formula"><sub>4</sub></span> absorption cross-sections covering the absorption band at 360 nm and laboratory measurements. While the best agreement is obtained for the <span class="cit" id="xref_text.1"><a href="#bib1.bibx2">Finkenzeller and Volkamer</a> (<a href="#bib1.bibx2">2022</a>)</span> cross-sections, deviations at cold ambient temperatures (below ca. <span class="inline-formula">−25</span> °C) are observed for the <span class="cit" id="xref_text.2"><a href="#bib1.bibx28">Thalman and Volkamer</a> (<a href="#bib1.bibx28">2013</a>)</span> cross-sections. Other O<span class="inline-formula"><sub>4</sub></span> absorption bands could not be investigated because these are not (fully) within the spectral range of the measured spectra. This study strongly supports the accuracy of commonly used O<span class="inline-formula"><sub>4</sub></span> absorption cross-sections in DOAS analyses, while more work is needed to understand the earlier reported inconsistencies in MAX-DOAS observations.</p> |
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| ISSN: | 1867-1381 1867-8548 |