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<article language="en">
	<journal>
		<journal_title>Atmospheric Chemistry and Physics Discussions</journal_title>
		<journal_url>www.atmos-chem-phys-discuss.net</journal_url>
		<issn>1680-7367</issn>
		<eissn>1680-7375</eissn>
		<volume_number>9</volume_number>
		<issue_number>5</issue_number>
		<publication_year>2009</publication_year>
	</journal>
	<doi>10.5194/acpd-9-22619-2009</doi>
	<article_url>http://www.atmos-chem-phys-discuss.net/9/22619/2009/</article_url>
	<abstract_html>http://www.atmos-chem-phys-discuss.net/9/22619/2009/acpd-9-22619-2009.html</abstract_html>
	<fulltext_pdf>http://www.atmos-chem-phys-discuss.net/9/22619/2009/acpd-9-22619-2009.pdf</fulltext_pdf>
	<start_page>22619</start_page>
	<end_page>22657</end_page>
	<publication_date>2009-10-26</publication_date>
	<article_title content_type="html">Widening the gap between measurement and modelling of secondary organic aerosol properties?</article_title>
	<authors>
		<author numeration="1" affiliations="1">
			<name>N. Good</name>
		</author>
		<author numeration="2" affiliations="1,2">
			<name>D. O. Topping</name>
		</author>
		<author numeration="3" affiliations="3,6">
			<name>J. Duplissy</name>
		</author>
		<author numeration="4" affiliations="3">
			<name>M. Gysel</name>
		</author>
		<author numeration="5" affiliations="4,5">
			<name>N. K. Meyer</name>
		</author>
		<author numeration="6" affiliations="3">
			<name>A. Metzger</name>
		</author>
		<author numeration="7" affiliations="1,7">
			<name>S. F. Turner</name>
		</author>
		<author numeration="8" affiliations="3">
			<name>U. Baltensperger</name>
		</author>
		<author numeration="9" affiliations="4">
			<name>Z. Ristovski</name>
		</author>
		<author numeration="10" affiliations="3">
			<name>E. Weingartner</name>
		</author>
		<author numeration="11" affiliations="1">
			<name>H. Coe</name>
		</author>
		<author numeration="12" affiliations="1">
			<name>G. McFiggans</name>
			<email>g.mcfiggans@manchester.ac.uk</email>
		</author>
	</authors>
	<affiliations>
		<affiliation numeration="1" content_type="html">School of Earth Atmospheric and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK</affiliation>
		<affiliation numeration="2" content_type="html">National Centre for Atmospheric Sciences, University of Manchester, Manchester, M13 9PL, UK</affiliation>
		<affiliation numeration="3" content_type="html">Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, 5232 Villigen, Switzerland</affiliation>
		<affiliation numeration="4" content_type="html">ILAQH, Queensland University of Technology, P.O. Box 4233, Brisbane QLD, 4001, Australia</affiliation>
		<affiliation numeration="5" content_type="html">now at: Laboratory for Energy Systems Analysis, Paul Scherrer Institut, 5232 Villigen, Switzerland</affiliation>
		<affiliation numeration="6" content_type="html">now at: Department of Physics, Centre Européen de la Recherche Nucléaire, 1211 Geneva, Switzerland</affiliation>
		<affiliation numeration="7" content_type="html">now at: Experimental Solid State Physics Group, Blackett Laboratory, Imperial College London, SW7 2BW, UK</affiliation>
	</affiliations>
	<abstract content_type="html">The link between measured sub-saturated hygroscopicity and cloud
      activation potential of secondary organic aerosol particles produced
      by the chamber photo-oxidation of &amp;alpha;-pinene in the presence
      or absence of ammonium sulphate seed aerosol was investigated using
      two models of varying complexity. A simple single hygroscopicity
      parameter model and a more complex model (incorporating surface
      effects) were used to assess the detail required to predict the cloud
      condensation nucleus (CCN) activity from the sub-saturated water
      uptake. Sub-saturated water uptake measured by three hygroscopicity
      tandem differential mobility analyser (HTDMA) instruments was used to
      determine the water activity for use in the models. The predicted CCN
      activity was compared to the measured CCN activation potential using
      a continuous flow CCN counter.
&lt;br&gt;&lt;br&gt;
      Reconciliation using the more complex model formulation with measured
      cloud activation required widely different assumed surface tension
      behavior of the growing droplet; this was entirely determined by the
      instrument used as the source of water activity data. This unreliable
      derivation of the water activity as a function of solute concentration
      from sub-saturated hygroscopicity data indicates a limitation in the
      use of such data in predicting cloud condensation nucleus behavior of
      particles with a significant organic fraction. Similarly, the ability
      of the simpler single parameter model to predict cloud activation
      behaviour was dependent on the instrument used to measure
      sub-saturated hygroscopicity and the relative humidity used to provide
      the model input. However, agreement was observed for inorganic salt
      solution particles, which were measured by all instruments in
      agreement with theory.
&lt;br&gt;&lt;br&gt;
      The difference in HTDMA data from proven instruments means that it
      cannot be stated with certainty the detail required to predict the CCN
      activity from sub-saturated hygroscopicity. In order to narrow the gap
      between measurements of hygroscopic growth and CCN activity the
      processes involved must be understood. It is impossible to say from
      the results presented here whether: i) Surface tension suppression
      occurs ii) Bulk to surface partitioning is important iii) The water
      activity coefficient changes significantly as a function of the solute
      concentration.</abstract>
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</article>

