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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-13-8973-2013</article-id>
<title-group>
<article-title>Measuring and modeling the hygroscopic growth of two humic substances in mixed aerosol particles of atmospheric relevance</article-title>
</title-group>
<contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Zamora</surname>
<given-names>I. R.</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>Jacobson</surname>
<given-names>M. Z.</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
</contrib-group><aff id="aff1">
<label>1</label>
<addr-line>Department of Geophysics, Stanford University Yang and  Yamazaki Environment and Energy Building, 473 Via Ortega, Room M05, Stanford, California 94305, USA</addr-line>
</aff>
<aff id="aff2">
<label>2</label>
<addr-line>Department of Civil and Environmental Engineering, Stanford University Yang and Yamazaki Environment and Energy Building, 473 Via Ortega, Room 397, Stanford, California 94305, USA</addr-line>
</aff>
<pub-date pub-type="epub">
<day>09</day>
<month>09</month>
<year>2013</year>
</pub-date>
<volume>13</volume>
<issue>17</issue>
<fpage>8973</fpage>
<lpage>8989</lpage>
<permissions>
<copyright-statement>Copyright: &#x000a9; 2013 I. R. Zamora</copyright-statement>
<copyright-year>2013</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/13/8973/2013/acp-13-8973-2013.html">This article is available from https://acp.copernicus.org/articles/13/8973/2013/acp-13-8973-2013.html</self-uri>
<self-uri xlink:href="https://acp.copernicus.org/articles/13/8973/2013/acp-13-8973-2013.pdf">The full text article is available as a PDF file from https://acp.copernicus.org/articles/13/8973/2013/acp-13-8973-2013.pdf</self-uri>
<abstract>
<p>The hygroscopic growth of atmospheric particles affects atmospheric chemistry
and Earth&apos;s climate. Water-soluble organic carbon (WSOC) constitutes a
significant fraction of the dry submicron mass of atmospheric aerosols, thus
affecting their water uptake properties. Although the WSOC fraction is
comprised of many compounds, a set of model substances can be used to
describe its behavior. For this study, mixtures of Nordic aquatic fulvic
acid reference (NAFA) and Fluka humic acid (HA), with various combinations of inorganic
salts (sodium chloride and ammonium sulfate) and other representative organic
compounds (levoglucosan and succinic acid), were studied. We measured the
equilibrium water vapor pressure over bulk solutions of these mixtures as a
function of temperature and solute concentration. New water activity
(&lt;i&gt;a&lt;/i&gt;&lt;sub&gt;w&lt;/sub&gt;) parameterizations and hygroscopic growth curves at
25 °C were calculated from these data for particles of equivalent
composition. We examined the effect of temperature on the water activity and
found a maximum variation of 9% in the 0–30 °C range, and
2% in the 20–30 °C range. Five two-component mixtures were
studied to understand the effect of adding a humic substance (HS), such as
NAFA and HA, to an inorganic salt or a saccharide. The deliquescence point at
25 °C for HS-inorganic mixtures did not change significantly from
that of the pure inorganic species. However, the hygroscopic growth of
HA / inorganic mixtures was lower than that exhibited by the pure salt, in
proportion to the added mass of HA. The addition of NAFA to a highly soluble
solute (ammonium sulfate, sodium chloride or levoglucosan) in water had the
same effect as the addition of HA to the inorganic species for most of the
water activity range studied. Yet, the water uptake of these NAFA mixtures
transitioned to match the growth of the pure salt or saccharide at high
&lt;i&gt;a&lt;/i&gt;&lt;sub&gt;w&lt;/sub&gt; values. The remaining four mixtures were based on chemical
composition data for different aerosol types. As expected, the two solutions
representing organic aerosols (40% HS/40% succinic acid/20%
levoglucosan) showed lower water uptake than the two solutions representing
biomass burning aerosols (25% HS/27% succinic acid/18%
levoglucosan/30% ammonium sulfate). However, interactions in
multicomponent solutions may be responsible for the large variation of the
relative water uptake of identical mixtures containing different HSs above a
water activity of 0.95. The ZSR (Zdanovskii, Stokes, and Robinson) model was able to predict reasonably well the
hygroscopic growth of all the mixtures below &lt;i&gt;a&lt;/i&gt;&lt;sub&gt;w&lt;/sub&gt; = 0.95, but
produced large deviations for some multicomponent mixtures at higher values.</p>
</abstract>
<counts><page-count count="17"/></counts>
</article-meta>
</front>
<body/>
<back>
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