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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>
<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-2026-5916</article-id>
<title-group>
<article-title>Retrieval of surface NO&lt;sub&gt;2&lt;/sub&gt; from Pandora direct sun measurements</article-title>
</title-group>
<contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Bates</surname>
<given-names>Darby</given-names>
<ext-link>https://orcid.org/0000-0003-0390-0234</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>Alwarda</surname>
<given-names>Ramina</given-names>
<ext-link>https://orcid.org/0000-0002-5983-6828</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>Zhao</surname>
<given-names>Xiaoyi</given-names>
<ext-link>https://orcid.org/0000-0003-4784-4502</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>Lee</surname>
<given-names>Sum Chi</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Griffin</surname>
<given-names>Debora</given-names>
<ext-link>https://orcid.org/0000-0002-4849-9125</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>Su</surname>
<given-names>Yushan</given-names>
</name>
<xref ref-type="aff" rid="aff4">
<sup>4</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Cede</surname>
<given-names>Alexander</given-names>
</name>
<xref ref-type="aff" rid="aff5">
<sup>5</sup>
</xref>
<xref ref-type="aff" rid="aff6">
<sup>6</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Strong</surname>
<given-names>Kimberly</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
</contrib-group><aff id="aff1">
<label>1</label>
<addr-line>Department of Physics, University of Toronto, Toronto, ON, M5S 1A7, Canada</addr-line>
</aff>
<aff id="aff2">
<label>2</label>
<addr-line>Atmospheric Composition Monitoring Division, Environment and Climate Change Canada, Toronto, ON, M3H 5T4,  Canada</addr-line>
</aff>
<aff id="aff3">
<label>3</label>
<addr-line>Earth Systems Research and Integration Division, Environment and Climate Change Canada, Toronto, ON, M3H  5T4, Canada</addr-line>
</aff>
<aff id="aff4">
<label>4</label>
<addr-line>Ontario Ministry of the Environment, Conservation, and Parks, Toronto, ON, M9P 3V6, Canada</addr-line>
</aff>
<aff id="aff5">
<label>5</label>
<addr-line>LuftBlick, Innsbruck, Austria</addr-line>
</aff>
<aff id="aff6">
<label>6</label>
<addr-line>NASA/GSFC Code 614, Greenbelt, MD, USA</addr-line>
</aff>
<pub-date pub-type="epub">
<day>09</day>
<month>11</month>
<year>2026</year>
</pub-date>
<volume>2026</volume>
<fpage>1</fpage>
<lpage>26</lpage>
<permissions>
<copyright-statement>Copyright: &#x000a9; 2026 Darby Bates et al.</copyright-statement>
<copyright-year>2026</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/2026/egusphere-2026-5916/">This article is available from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-5916/</self-uri>
<self-uri xlink:href="https://egusphere.copernicus.org/preprints/2026/egusphere-2026-5916/egusphere-2026-5916.pdf">The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-5916/egusphere-2026-5916.pdf</self-uri>
<abstract>
<p>Nitrogen dioxide (NO&lt;sub&gt;2&lt;/sub&gt;), a criteria pollutant used for the Air Quality Health Index (AQHI) reporting, can have important environmental and human respiratory health effects when present in the near-surface atmosphere. For this study, urban surface volume mixing ratios (VMRs) are derived from Pandora total column measurements. Pandora remote sensing instruments can be used to evaluate surface air quality and complement in situ instruments to support long-term monitoring of ambient air quality. At four sites in the Greater Toronto Area and Detroit-Windsor Area, Pandora direct sun measurements are converted to surface VMRs following a method utilizing a high-resolution air quality forecasting model. The resulting VMRs agree with coincident in situ measurements to within 2 ppbv from 2020 through 2024. This method is shown to be most effective when the Planetary Boundary Layer (PBL) is above 750 m as estimated by ERA5 reanalysis, while dependence on PBL height below 750 m is evaluated. The surface VMR derived from Pandora direct sun measurements when the PBL is below 750 m has a median difference of -1.7 ppbv (parts per billion by volume) (10&lt;sup&gt;th&lt;/sup&gt; percentile: -8.2 ppbv, 90&lt;sup&gt;th&lt;/sup&gt; percentile: 3.2 ppbv) with respect to coincident in situ measurements. When a logarithmic correction is applied as a function of PBL height for these shallow PBL conditions, the median difference is reduced to 0.5 ppbv (-4.8 ppbv, 4.1 ppbv).</p>
</abstract>
<counts><page-count count="26"/></counts>
<funding-group>
<award-group id="gs1">
<funding-source>Environment and Climate Change Canada</funding-source>
<award-id>GCXE22S069</award-id>
</award-group>
</funding-group>
</article-meta>
</front>
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