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<front>
<journal-meta>
<journal-id journal-id-type="publisher">ACP</journal-id>
<journal-title-group>
<journal-title>Atmospheric Chemistry and Physics</journal-title>
<abbrev-journal-title abbrev-type="publisher">ACP</abbrev-journal-title>
<abbrev-journal-title abbrev-type="nlm-ta">Atmos. Chem. Phys.</abbrev-journal-title>
</journal-title-group>
<issn pub-type="epub">1680-7324</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/acp-14-6925-2014</article-id>
<title-group>
<article-title>Factors controlling pollutant plume length downwind of major roadways in nocturnal surface inversions</article-title>
</title-group>
<contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Choi</surname>
<given-names>W.</given-names>
<ext-link>https://orcid.org/0000-0003-2988-7242</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>Winer</surname>
<given-names>A. M.</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>Paulson</surname>
<given-names>S. E.</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
</contrib-group><aff id="aff1">
<label>1</label>
<addr-line>University of California, Los Angeles, Department of Atmospheric and Oceanic Sciences, Los Angeles, California, USA</addr-line>
</aff>
<aff id="aff2">
<label>2</label>
<addr-line>University of California, Los Angeles, School of Public Health, Environmental Health Sciences Department, Los Angeles, California, USA</addr-line>
</aff>
<pub-date pub-type="epub">
<day>04</day>
<month>07</month>
<year>2014</year>
</pub-date>
<volume>14</volume>
<issue>13</issue>
<fpage>6925</fpage>
<lpage>6940</lpage>
<permissions>
<copyright-statement>Copyright: &#x000a9; 2014 W. Choi et al.</copyright-statement>
<copyright-year>2014</copyright-year>
<license license-type="open-access">
<license-p>This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit <ext-link ext-link-type="uri"  xlink:href="https://creativecommons.org/licenses/by/3.0/">https://creativecommons.org/licenses/by/3.0/</ext-link></license-p>
</license>
</permissions>
<self-uri xlink:href="https://acp.copernicus.org/articles/14/6925/2014/acp-14-6925-2014.html">This article is available from https://acp.copernicus.org/articles/14/6925/2014/acp-14-6925-2014.html</self-uri>
<self-uri xlink:href="https://acp.copernicus.org/articles/14/6925/2014/acp-14-6925-2014.pdf">The full text article is available as a PDF file from https://acp.copernicus.org/articles/14/6925/2014/acp-14-6925-2014.pdf</self-uri>
<abstract>
<p>A fitting method using a semi-empirical Gaussian dispersion model solution
was successfully applied to obtain both dispersion coefficients and a
particle number emission factor (PNEF) directly from ultrafine particle (UFP;
particles smaller than &lt;0.1 μm in diameter) concentration
profiles observed downwind of major roadways in California&apos;s South Coast Air
Basin (SoCAB). The effective Briggs&apos; formulation for the vertical dispersion
parameter &amp;sigma;&lt;sub&gt;z&lt;/sub&gt; was adopted in this study due to its better
performance in describing the observed profiles compared to other
formulations examined. The two dispersion coefficients in Briggs&apos;
formulation, α and β, ranged from 0.02 to 0.07 and from
−0.5 × 10&lt;sup&gt;−3&lt;/sup&gt; to 2.8 × 10&lt;sup&gt;−3&lt;/sup&gt;, respectively, for
the four freeway transects studied and are significantly different for
freeways passing over vs. under the street on which measurements of the
freeway plume were made. These ranges are wider than literature values for
α and β under stable conditions. The dispersion coefficients
derived from observations showed strong correlations with both surface
meteorology (wind speed/direction, temperature, and air stability) and
differences in concentrations between the background and plume peak. The
relationships were applied to predict freeway plume transport using a
multivariate regression, and produced excellent agreement with observed UFP
concentration profiles. The mean PNEF for a mixed vehicle fleet on the four
freeways was estimated as
7.5 × 10&lt;sup&gt;13&lt;/sup&gt; particles km&lt;sup&gt;−1&lt;/sup&gt; vehicle&lt;sup&gt;−1&lt;/sup&gt;, which is
about 15% of the value estimated in 2001 for the I-405 freeway, implying
significant reductions in UFP emissions over the past decade in the SoCAB.</p>
</abstract>
<counts><page-count count="16"/></counts>
</article-meta>
</front>
<body/>
<back>
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