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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>3</issue_number>
		<publication_year>2009</publication_year>
	</journal>
	<doi>10.5194/acpd-9-12519-2009</doi>
	<article_url>http://www.atmos-chem-phys-discuss.net/9/12519/2009/</article_url>
	<abstract_html>http://www.atmos-chem-phys-discuss.net/9/12519/2009/acpd-9-12519-2009.html</abstract_html>
	<fulltext_pdf>http://www.atmos-chem-phys-discuss.net/9/12519/2009/acpd-9-12519-2009.pdf</fulltext_pdf>
	<start_page>12519</start_page>
	<end_page>12558</end_page>
	<publication_date>2009-05-26</publication_date>
	<article_title content_type="html">Aerosol optical properties relevant to regional remote sensing of CCN activity and links to their organic mass fraction: airborne observations over Central Mexico and the US West Coast during MILAGRO/INTEX-B</article_title>
	<authors>
		<author numeration="1" affiliations="1,7">
			<name>Y. Shinozuka</name>
			<email>yohei@hawaii.edu</email>
		</author>
		<author numeration="2" affiliations="1">
			<name>A. D. Clarke</name>
		</author>
		<author numeration="3" affiliations="2,3,8">
			<name>P. F. DeCarlo</name>
		</author>
		<author numeration="4" affiliations="2,4">
			<name>J. L. Jimenez</name>
		</author>
		<author numeration="5" affiliations="2">
			<name>E. J. Dunlea</name>
		</author>
		<author numeration="6" affiliations="5">
			<name>G. C. Roberts</name>
		</author>
		<author numeration="7" affiliations="6">
			<name>J. M. Tomlinson</name>
		</author>
		<author numeration="8" affiliations="6">
			<name>D. R. Collins</name>
		</author>
		<author numeration="9" affiliations="1">
			<name>S. G. Howell</name>
		</author>
		<author numeration="10" affiliations="1">
			<name>V. N. Kapustin</name>
		</author>
		<author numeration="11" affiliations="1">
			<name>C. S. McNaughton</name>
		</author>
		<author numeration="12" affiliations="1">
			<name>J. Zhou</name>
		</author>
	</authors>
	<affiliations>
		<affiliation numeration="1" content_type="html">School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI, USA</affiliation>
		<affiliation numeration="2" content_type="html">Cooperative Institute for Research in the Environmental Sciences, University of Colorado, Boulder, CO, USA</affiliation>
		<affiliation numeration="3" content_type="html">Dept. of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO, USA</affiliation>
		<affiliation numeration="4" content_type="html">Dept. of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA</affiliation>
		<affiliation numeration="5" content_type="html">Center for Atmospheric Sciences, Scripps Institution of Oceanography, La Jolla, CA, USA</affiliation>
		<affiliation numeration="6" content_type="html">Department of Atmospheric Sciences, Texas A{&amp;}M University, College Station, TX, USA</affiliation>
		<affiliation numeration="7" content_type="html">now at: National Aeronautics and Space Administration Ames Research Center, MS 245-5, Moffett Field, CA, USA</affiliation>
		<affiliation numeration="8" content_type="html">now at: Paul Scherrer Institut, 5232 Villigen-PSI, Switzerland</affiliation>
	</affiliations>
	<abstract content_type="html">Remote sensing of cloud condensation nuclei (CCN) would help evaluate the
indirect effects of tropospheric aerosols on clouds and climate. To assess
its feasibility, we examined relationships of submicron aerosol composition
to CCN activity and optical properties observed during the MILAGRO/INTEX-B
aircraft campaigns. An indicator of CCN activity, κ, was calculated from
hygroscopicity measured under saturation. κ for dry 100-nm particles
decreased with the organic fraction of non-refractory mass of submicron
particles (OMF) as 10&lt;sup&gt;(&amp;minus;0.43&amp;minus;0.44*OMF)&lt;/sup&gt; over Central Mexico and
10&lt;sup&gt;(&amp;minus;0.29&amp;minus;0.70*OMF)&lt;/sup&gt; over the US West Coast. These fits represent the
critical dry diameter, centered near 100 nm for 0.2% supersaturation but
varied as &amp;kappa;&lt;sup&gt;(&amp;minus;1/3)&lt;/sup&gt;, within measurement uncertainty (~20%). The
decreasing trends of CCN activity with the organic content, evident also in
our direct CCN counts, were consistent with previous ground and laboratory
observations of highly organic particles. The wider range of OMF, 0–0.8,
for our research areas means that aerosol composition will be more critical
for estimation of CCN concentration than at the fixed sites previously
studied. Furthermore, the wavelength dependence of extinction was
anti-correlated with OMF as &amp;minus;0.70*OMF+2.0 for Central Mexico&apos;s urban and
industrial pollution air masses, for unclear reasons. The Angstrom exponent
of absorption increased with OMF, more rapidly under higher single
scattering albedo, as expected for the interplay between soot and colored
weak absorbers (some organic species and dust). Because remote sensing
products currently use the wavelength dependence of extinction albeit in the
column integral form and may potentially include that of absorption, these
regional spectral dependencies are expected to facilitate retrievals of
aerosol bulk chemistry and CCN activity over Central Mexico.</abstract>
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</article>

