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<article language="en">
	<journal>
		<journal_title>Atmospheric Measurement Techniques Discussions</journal_title>
		<journal_url>www.atmos-meas-tech-discuss.net</journal_url>
		<eissn>1867-8610</eissn>
		<volume_number>2</volume_number>
		<issue_number>6</issue_number>
		<publication_year>2009</publication_year>
	</journal>
	<doi>10.5194/amtd-2-3221-2009</doi>
	<article_url>http://www.atmos-meas-tech-discuss.net/2/3221/2009/</article_url>
	<abstract_html>http://www.atmos-meas-tech-discuss.net/2/3221/2009/amtd-2-3221-2009.html</abstract_html>
	<fulltext_pdf>http://www.atmos-meas-tech-discuss.net/2/3221/2009/amtd-2-3221-2009.pdf</fulltext_pdf>
	<start_page>3221</start_page>
	<end_page>3264</end_page>
	<publication_date>2009-12-11</publication_date>
	<article_title content_type="html">On the improvement of NO&lt;sub&gt;2&lt;/sub&gt; satellite retrievals – aerosol impact on the airmass factors</article_title>
	<authors>
		<author numeration="1" affiliations="1">
			<name>J. Leitão</name>
			<email>jleitao@iup.physik.uni-bremen.de</email>
		</author>
		<author numeration="2" affiliations="1">
			<name>A. Richter</name>
		</author>
		<author numeration="3" affiliations="1">
			<name>M. Vrekoussis</name>
		</author>
		<author numeration="4" affiliations="1">
			<name>A. Kokhanovsky</name>
		</author>
		<author numeration="5" affiliations="2">
			<name>Q. J. Zhang</name>
		</author>
		<author numeration="6" affiliations="2">
			<name>M. Beekmann</name>
		</author>
		<author numeration="7" affiliations="1">
			<name>J. P. Burrows</name>
		</author>
	</authors>
	<affiliations>
		<affiliation numeration="1" content_type="html">Institute of Environmental Physics, University of Bremen, Bremen, Germany</affiliation>
		<affiliation numeration="2" content_type="html">Laboratoire Inter-Universitaire des Systèmes Atmosphèriques (LISA), CNRS et Universités Paris 12 et Paris 7, Créteil, France</affiliation>
	</affiliations>
	<abstract content_type="html">The accurate determination of nitrogen dioxide (NO&lt;sub&gt;2&lt;/sub&gt;) tropospheric
vertical columns from satellite measurements depends, partly, on the airmass
factor (AMF) used. A sensitivity study was performed with the radiative
transfer model SCIATRAN to better understand the impact of aerosols in the
calculation of NO&lt;sub&gt;2&lt;/sub&gt; AMFs. This influence was studied by varying the
NO&lt;sub&gt;2&lt;/sub&gt; and aerosol vertical distributions, as well as physical and optical
properties of the particles. The key factors for these calculations were
identified as the relation between trace gas and aerosol vertical profiles,
the optical depth of the aerosol layer, and single scattering albedo.
Overall it was found that aerosol mixed with the trace gas increases the
measurements&apos; sensitivity. The largest change, a factor of ~2 relative
to the situation without aerosols, was found when a low layer of aerosol
(600 m) was combined with a homogenous NO&lt;sub&gt;2&lt;/sub&gt; layer of 1.0 km. A layer of
aerosol above the NO&lt;sub&gt;2&lt;/sub&gt; will usually reduce the sensitivity of the
satellite measurement, a situation found mostly for runs with discrete
elevated aerosol layers representative for long-range transport of aerosols
that can generate a decrease of the AMF values of up to 70%. The use of
measured aerosol profiles and modelled NO&lt;sub&gt;2&lt;/sub&gt; resulted, generally, in a
much smaller changes of AMF relative to the pure Rayleigh case. Exceptions
are some events of elevated layers with high aerosol optical depth that lead
to a strong decrease of the AMF values. These results highlight the
importance of aerosols in the retrieval of tropospheric NO&lt;sub&gt;2&lt;/sub&gt; columns
from space and indicate the need for detailed information on aerosol
properties and vertical distribution.</abstract>
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</article>

