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<front>
<journal-meta>
<journal-id journal-id-type="publisher">ACPD</journal-id>
<journal-title-group>
<journal-title>Atmospheric Chemistry and Physics Discussions</journal-title>
<abbrev-journal-title abbrev-type="publisher">ACPD</abbrev-journal-title>
</journal-title-group>
<issn pub-type="epub">1680-7375</issn>
<publisher><publisher-name>Copernicus GmbH</publisher-name>
<publisher-loc>Göttingen, Germany</publisher-loc>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.5194/acpd-12-9903-2012</article-id>
<title-group>
<article-title>Deliquescence, efflorescence, and phase miscibility of mixed particles of ammonium sulfate and isoprene-derived secondary organic material</article-title>
</title-group>
<contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Smith</surname>
<given-names>M. L.</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>Bertram</surname>
<given-names>A. K.</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>Martin</surname>
<given-names>S. T.</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
</contrib-group><aff id="aff1">
<label>1</label>
<addr-line>School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA</addr-line>
</aff>
<aff id="aff2">
<label>2</label>
<addr-line>Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada</addr-line>
</aff>
<aff id="aff3">
<label>3</label>
<addr-line>Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA</addr-line>
</aff>
<pub-date pub-type="epub">
<day>18</day>
<month>04</month>
<year>2012</year>
</pub-date>
<volume>12</volume>
<issue>4</issue>
<fpage>9903</fpage>
<lpage>9943</lpage>
<permissions>
<license xlink:type="simple">
<license-p>This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.</license-p>
</license>
</permissions>
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<abstract>
<p>The hygroscopic phase transitions of ammonium sulfate mixed with
isoprene-derived secondary organic material were investigated in aerosol
experiments. The organic material was produced by isoprene photo-oxidation
at 40% relative humidity. The low volatility fraction of the
photo-oxidation products condensed onto ammonium sulfate particles. The
particle-phase organic material had oxygen-to-carbon ratios of 0.67 to 0.74
for mass concentrations of 20 to 30 μg m&lt;sup&gt;&amp;minus;3&lt;/sup&gt;. The deliquescence,
efflorescence, and phase miscibility of the mixed particles were
investigated using a dual arm tandem differential mobility analyzer. The
isoprene photo-oxidation products induced deviations in behavior relative to
pure ammonium sulfate. Compared to an efflorescence relative humidity (ERH)
of 30 to 35% for pure ammonium sulfate, efflorescence was eliminated for
mixed aqueous particles having organic volume fractions ε of approximately
0.6 and greater. Compared to a deliquescence relative humidity (DRH) of
80% for pure ammonium sulfate, the DRH steadily decreased for increasing
ε, approaching a DRH of 40% for ε of 0.9. Parameterizations of the
DRH(ε) and ERH(ε) curves were as follows: DRH(ε)= &amp;Sigma; &lt;sub&gt;&lt;i&gt;i&lt;/i&gt;&lt;/sub&gt; &lt;i&gt;c&lt;sub&gt;i,d&lt;/sub&gt; x&lt;sup&gt;i&lt;/sup&gt;&lt;/i&gt;
valid for 0 ≤ ε ≤  0.86 and ERH(ε)= &amp;Sigma; &lt;sub&gt;&lt;i&gt;i&lt;/i&gt;&lt;/sub&gt; &lt;i&gt;c&lt;sub&gt;i,e&lt;/sub&gt; x&lt;sup&gt;i&lt;/sup&gt;&lt;/i&gt; valid for
0 ≤  ε  ≤  0.55 for the coefficients &lt;i&gt;c&lt;sub&gt;0,d&lt;/sub&gt;&lt;/i&gt;= 80.67, &lt;i&gt;c&lt;sub&gt;0,e&lt;/sub&gt;&lt;/i&gt; = 28.35,
&lt;i&gt;c&lt;sub&gt;1,d&lt;/sub&gt;&lt;/i&gt;= &amp;minus;11.45, &lt;i&gt;c&lt;sub&gt;1,e&lt;/sub&gt;&lt;/i&gt; = &amp;minus;13.66, &lt;i&gt;c&lt;sub&gt;2,d&lt;/sub&gt;&lt;/i&gt; = 0, &lt;i&gt;c&lt;sub&gt;2,e&lt;/sub&gt;&lt;/i&gt; = 0,
&lt;i&gt;c&lt;sub&gt;3,d&lt;/sub&gt;&lt;/i&gt; = 57.99, &lt;i&gt;c&lt;sub&gt;3,e&lt;/sub&gt;&lt;/i&gt; = &amp;minus;83.80, &lt;i&gt;c&lt;sub&gt;4,d&lt;/sub&gt;&lt;/i&gt; = &amp;minus;106.80, and &lt;i&gt;c&lt;sub&gt;4,d&lt;/sub&gt;&lt;/i&gt; =
0.
The molecular description that is thermodynamically implied by these
strongly sloped DRH(ε) and ERH(ε) curves is that the organic isoprene
photo-oxidation products, the inorganic ammonium sulfate, and water form a
miscible liquid phase even at low relative humidity. This phase miscibility
is in contrast to the liquid-liquid separation that occurs for some other
types of secondary organic material. These differences in liquid-liquid
separation are consistent with a prediction recently presented in the
literature that the bifurcation between liquid-liquid phase separation
versus mixing depends on the oxygen-to-carbon ratio of the organic material.
The conclusions are that the influence of secondary organic material on the
hygroscopic properties of ammonium sulfate varies with organic composition
and that the degree of oxygenation of the organic material, which is a
measurable characteristic of complex organic materials, is an important
variable influencing the hygroscopic properties of mixed organic-inorganic
particles.</p>
</abstract>
<counts><page-count count="41"/></counts>
</article-meta>
</front>
<body/>
<back>
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