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<article language="en">
	<journal>
		<journal_title>Atmospheric Chemistry and Physics</journal_title>
		<journal_url>www.atmos-chem-phys.net</journal_url>
		<issn>1680-7316</issn>
		<eissn>1680-7324</eissn>
		<volume_number>8</volume_number>
		<issue_number>5</issue_number>
		<publication_year>2008</publication_year>
	</journal>
	<doi>10.5194/acp-8-1153-2008</doi>
	<article_url>http://www.atmos-chem-phys.net/8/1153/2008/</article_url>
	<abstract_html>http://www.atmos-chem-phys.net/8/1153/2008/acp-8-1153-2008.html</abstract_html>
	<fulltext_pdf>http://www.atmos-chem-phys.net/8/1153/2008/acp-8-1153-2008.pdf</fulltext_pdf>
	<start_page>1153</start_page>
	<end_page>1179</end_page>
	<publication_date>2008-02-29</publication_date>
	<article_title content_type="html">Calibration and measurement uncertainties of a continuous-flow cloud  condensation nuclei counter (DMT-CCNC): CCN activation of ammonium sulfate  and sodium chloride aerosol particles in theory and experiment</article_title>
	<authors>
		<author numeration="1" affiliations="1">
			<name>D. Rose</name>
			<email>rose@mpch-mainz.mpg.de</email>
		</author>
		<author numeration="2" affiliations="1">
			<name>S. S. Gunthe</name>
		</author>
		<author numeration="3" affiliations="1,2">
			<name>E. Mikhailov</name>
		</author>
		<author numeration="4" affiliations="1,3">
			<name>G. P. Frank</name>
		</author>
		<author numeration="5" affiliations="1,4">
			<name>U. Dusek</name>
		</author>
		<author numeration="6" affiliations="1">
			<name>M. O. Andreae</name>
		</author>
		<author numeration="7" affiliations="1">
			<name>U. Pöschl</name>
		</author>
	</authors>
	<affiliations>
		<affiliation numeration="1" content_type="html">Max Planck Institute for Chemistry, Biogeochemistry Department, P.O. Box 3060, 55020 Mainz, Germany</affiliation>
		<affiliation numeration="2" content_type="html">Atmospheric Physics Department, Institute of Physics, St. Petersburg State University, 198904 St. Petersburg, Russia</affiliation>
		<affiliation numeration="3" content_type="html">now at: Lund University, Department of Physics, Lund, Sweden</affiliation>
		<affiliation numeration="4" content_type="html">now at: IMAU, Utrecht University, Utrecht, The Netherlands</affiliation>
	</affiliations>
	<abstract content_type="html">Experimental and theoretical uncertainties in the measurement of cloud
condensation nuclei (CCN) with a continuous-flow thermal-gradient CCN counter
from Droplet Measurement Technologies (DMT-CCNC) have been assessed by model
calculations and calibration experiments with ammonium sulfate and sodium
chloride aerosol particles in the diameter range of 20&amp;ndash;220 nm. Experiments
have been performed in the laboratory and during field measurement campaigns,
covering a wide range of instrument operating conditions (650&amp;ndash;1020 hPa
pressure, 293&amp;ndash;303 K inlet temperature, 4&amp;ndash;34 K m&lt;sup&gt;&amp;minus;1&lt;/sup&gt; temperature
gradient, 0.5&amp;ndash;1.0 L min&lt;sup&gt;&amp;minus;1&lt;/sup&gt; flow rate). For each set of conditions, the
effective water vapor supersaturation (&lt;I&gt;S&lt;/I&gt;&lt;sub&gt;eff&lt;/sub&gt;, 0.05&amp;ndash;1.4%) was
determined from the measured CCN activation spectra (dry particle activation
diameters) and Köhler model calculations. High measurement precision was
achieved under stable laboratory conditions, where the relative standard
deviations of &lt;I&gt;S&lt;/I&gt;&lt;sub&gt;eff&lt;/sub&gt; were as low as &amp;plusmn;1%. During field
measurements, however, the relative deviations increased to about &amp;plusmn;5%,
which can be mostly attributed to variations of the CCNC column top
temperature with ambient temperature. The observed dependence of &lt;I&gt;S&lt;/I&gt;&lt;sub&gt;eff&lt;/sub&gt; 
on temperature, pressure, and flow rate was compared to the CCNC flow
model of Lance et al. (2006). At high &lt;I&gt;S&lt;/I&gt;&lt;sub&gt;eff&lt;/sub&gt; the relative deviations
between flow model and experimental results were mostly less than 10%, but
at &lt;I&gt;S&lt;/I&gt;&lt;sub&gt;eff&lt;/sub&gt;&amp;le;0.1% they exceeded 40%. Thus, careful experimental
calibration is required for high-accuracy CCN measurements &amp;ndash; especially at
low &lt;I&gt;S&lt;/I&gt;&lt;sub&gt;eff&lt;/sub&gt;. A comprehensive comparison and uncertainty analysis of the
various Köhler models and thermodynamic parameterizations commonly used
in CCN studies showed that the relative deviations between different
approaches are as high as 25% for (NH&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt; and 12% for NaCl.
The deviations were mostly caused by the different parameterizations for the
activity of water in aqueous solutions of the two salts. To ensure
comparability of results, we suggest that CCN studies should always report
exactly which Köhler model equations and parameters were used. Provided
that the Aerosol Inorganics Model (AIM) can be regarded as an accurate source
of water activity data for highly dilute solutions of (NH&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt; and
NaCl, only Köhler models that are based on the AIM or yield similar
results should be used in CCN studies involving these salts and aiming at
high accuracy. Experiments with (NH&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt; and NaCl aerosols showed
that the conditions of particle generation and the shape and microstructure
of NaCl particles are critical for their application in CCN activation
experiments (relative deviations up to 18%).</abstract>
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</article>

