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<front>
<journal-meta>
<journal-id journal-id-type="publisher">EGUsphere</journal-id>
<journal-title-group>
<journal-title>EGUsphere</journal-title>
<abbrev-journal-title abbrev-type="publisher">EGUsphere</abbrev-journal-title>
<abbrev-journal-title abbrev-type="nlm-ta">EGUsphere</abbrev-journal-title>
</journal-title-group>
<issn pub-type="epub">1867-8610</issn>
<publisher><publisher-name>Copernicus Publications</publisher-name>
<publisher-loc>Göttingen, Germany</publisher-loc>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.5194/egusphere-2025-4026</article-id>
<title-group>
<article-title>Enhanced characterization of SO&lt;sub&gt;2&lt;/sub&gt; plume height and column density using the second UV spectral band of TROPOMI</article-title>
</title-group>
<contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Fabris</surname>
<given-names>Lorenzo</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Theys</surname>
<given-names>Nicolas</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Clarisse</surname>
<given-names>Lieven</given-names>
<ext-link>https://orcid.org/0000-0002-8805-2141</ext-link>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Franco</surname>
<given-names>Bruno</given-names>
<ext-link>https://orcid.org/0000-0003-0736-458X</ext-link>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Vlietinck</surname>
<given-names>Jonas</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Yu</surname>
<given-names>Huan</given-names>
<ext-link>https://orcid.org/0000-0002-0447-4284</ext-link>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Brenot</surname>
<given-names>Hugues</given-names>
<ext-link>https://orcid.org/0000-0002-5812-0377</ext-link>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Danckaert</surname>
<given-names>Thomas</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Hedelt</surname>
<given-names>Pascal</given-names>
<ext-link>https://orcid.org/0000-0002-1752-0040</ext-link>
</name>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Van Roozendael</surname>
<given-names>Michel</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
</contrib-group><aff id="aff1">
<label>1</label>
<addr-line>UV-VIS observations, Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium</addr-line>
</aff>
<aff id="aff2">
<label>2</label>
<addr-line>Spectroscopy, Quantum Chemistry and Atmospheric Remote Sensing (SQUARES), Brussels Laboratory of the Universe (BLU-ULB), Université Libre de Bruxelles (ULB), Brussels, Belgium</addr-line>
</aff>
<aff id="aff3">
<label>3</label>
<addr-line>Institut für Methodik der Fernerkundung (IMF), Deutsches Zentrum für Luft und Raumfahrt (DLR), Oberpfaffenhofen, Germany</addr-line>
</aff>
<pub-date pub-type="epub">
<day>28</day>
<month>08</month>
<year>2025</year>
</pub-date>
<volume>2025</volume>
<fpage>1</fpage>
<lpage>37</lpage>
<permissions>
<copyright-statement>Copyright: &#x000a9; 2025 Lorenzo Fabris et al.</copyright-statement>
<copyright-year>2025</copyright-year>
<license license-type="open-access">
<license-p>This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit <ext-link ext-link-type="uri"  xlink:href="https://creativecommons.org/licenses/by/4.0/">https://creativecommons.org/licenses/by/4.0/</ext-link></license-p>
</license>
</permissions>
<self-uri xlink:href="https://egusphere.copernicus.org/preprints/2025/egusphere-2025-4026/">This article is available from https://egusphere.copernicus.org/preprints/2025/egusphere-2025-4026/</self-uri>
<self-uri xlink:href="https://egusphere.copernicus.org/preprints/2025/egusphere-2025-4026/egusphere-2025-4026.pdf">The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2025/egusphere-2025-4026/egusphere-2025-4026.pdf</self-uri>
<abstract>
<p>Volcanic emissions of sulfur dioxide (SO&lt;sub&gt;2&lt;/sub&gt;) affect the environment, climate, and society. Their detection and quantification rely extensively on remote sensing techniques, which are used to track SO&lt;sub&gt;2&lt;/sub&gt; and monitor volcanic activity worldwide. In particular, nadir-viewing satellites measuring total SO&lt;sub&gt;2&lt;/sub&gt; vertical column densities (VCDs) have provided valuable insights into volcanic emissions for decades. However, the determination of the SO&lt;sub&gt;2&lt;/sub&gt; layer height (LH) is more challenging. In this study, we present an improved SO&lt;sub&gt;2&lt;/sub&gt; LH (and VCD) retrieval algorithm, applicable to the second UV spectral band (BD2) of the TROPOspheric Monitoring Instrument (TROPOMI). This band exhibits a stronger SO&lt;sub&gt;2&lt;/sub&gt; absorption than the third band (BD3) that is traditionally used for SO&lt;sub&gt;2 &lt;/sub&gt;retrievals. To assess the impact of various spectral, atmospheric, and observation conditions, we conducted sensitivity analyses from a set of synthetic spectra representative of TROPOMI measurements using the Look-Up Table COvariance-Based Retrieval Algorithm (LUT-COBRA). Our results demonstrate that BD2 retrievals result in more accurate estimates of the SO&lt;sub&gt;2&lt;/sub&gt; heights and columns, particularly in the upper troposphere and lower stratosphere (UTLS), with LH errors reduced by at least a factor of 2. The algorithm was applied to real TROPOMI observations from volcanic eruptions and degassing episodes, and compared to BD3 retrievals. BD2 shows an improved sensitivity, with less noise, and a detection limit as low as 2 DU, surpassing the current operational TROPOMI SO&lt;sub&gt;2&lt;/sub&gt; product by an order of magnitude. Furthermore, our plume height estimates align closely with independent measurements from the Infrared Atmospheric Sounding Interferometer (IASI) and Microwave Limb Sounder (MLS), confirming the reliability of the approach.</p>
</abstract>
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