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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>7</volume_number>
		<issue_number>8</issue_number>
		<publication_year>2007</publication_year>
	</journal>
	<doi>10.5194/acp-7-2103-2007</doi>
	<article_url>http://www.atmos-chem-phys.net/7/2103/2007/</article_url>
	<abstract_html>http://www.atmos-chem-phys.net/7/2103/2007/acp-7-2103-2007.html</abstract_html>
	<fulltext_pdf>http://www.atmos-chem-phys.net/7/2103/2007/acp-7-2103-2007.pdf</fulltext_pdf>
	<start_page>2103</start_page>
	<end_page>2118</end_page>
	<publication_date>2007-04-27</publication_date>
	<article_title content_type="html">Near-real time retrieval of tropospheric NO&lt;sub&gt;2&lt;/sub&gt; from OMI</article_title>
	<authors>
		<author numeration="1" affiliations="1,3">
			<name>K. F. Boersma</name>
			<email>boersma@fas.harvard.edu</email>
		</author>
		<author numeration="2" affiliations="1">
			<name>H. J. Eskes</name>
		</author>
		<author numeration="3" affiliations="1">
			<name>J. P. Veefkind</name>
		</author>
		<author numeration="4" affiliations="1">
			<name>E. J. Brinksma</name>
		</author>
		<author numeration="5" affiliations="1">
			<name>R. J. van der A</name>
		</author>
		<author numeration="6" affiliations="1">
			<name>M. Sneep</name>
		</author>
		<author numeration="7" affiliations="1">
			<name>G. H. J. van den Oord</name>
		</author>
		<author numeration="8" affiliations="1">
			<name>P. F. Levelt</name>
		</author>
		<author numeration="9" affiliations="1">
			<name>P. Stammes</name>
		</author>
		<author numeration="10" affiliations="2">
			<name>J. F. Gleason</name>
		</author>
		<author numeration="11" affiliations="2">
			<name>E. J. Bucsela</name>
		</author>
	</authors>
	<affiliations>
		<affiliation numeration="1" content_type="html">KNMI, De Bilt, The Netherlands</affiliation>
		<affiliation numeration="2" content_type="html">NASA GSFC, Greenbelt, MD, USA</affiliation>
		<affiliation numeration="3" content_type="html">now at: Harvard University, Cambridge, USA</affiliation>
	</affiliations>
	<abstract content_type="html">We present a new algorithm for the near-real
time retrieval &amp;ndash; within 3 h of the actual satellite
measurement &amp;ndash; of tropospheric NO&lt;sub&gt;2&lt;/sub&gt; columns from
the Ozone Monitoring Instrument (OMI). The retrieval is
based on the combined retrieval-assimilation-modelling
approach developed at KNMI for off-line tropospheric NO&lt;sub&gt;2&lt;/sub&gt;
from the GOME and SCIAMACHY satellite instruments. We have adapted
the off-line system such that the required a priori information &amp;ndash; profile shapes
and stratospheric background NO&lt;sub&gt;2&lt;/sub&gt; &amp;ndash; is now immediately available upon arrival
(within 80 min of observation) of the OMI NO&lt;sub&gt;2&lt;/sub&gt; slant columns and cloud data at
KNMI. Slant columns for NO&lt;sub&gt;2&lt;/sub&gt; are retrieved using differential optical
absorption spectroscopy (DOAS) in the 405&amp;ndash;465 nm range. Cloud fraction
and cloud pressure are provided by a new cloud retrieval algorithm that uses
the absorption of the O&lt;sub&gt;2&lt;/sub&gt;-O&lt;sub&gt;2&lt;/sub&gt; collision complex near 477 nm.
On-line availability of stratospheric slant columns and NO&lt;sub&gt;2&lt;/sub&gt; profiles
is achieved by running the TM4 chemistry transport model (CTM) forward in
time based on forecast ECMWF meteo and assimilated NO&lt;sub&gt;2&lt;/sub&gt; information
from all previously observed orbits. OMI NO&lt;sub&gt;2&lt;/sub&gt; slant columns, after
correction for spurious across-track variability, show a random error for
individual pixels of approximately 0.7&amp;times;10&lt;sup&gt;15&lt;/sup&gt; molec cm&lt;sup&gt;&amp;minus;2&lt;/sup&gt;.
Cloud parameters from OMI&apos;s O&lt;sub&gt;2&lt;/sub&gt;-O&lt;sub&gt;2&lt;/sub&gt; algorithm have similar frequency distributions as
retrieved from SCIAMACHY&apos;s Fast Retrieval Scheme for Cloud Observables (FRESCO) for August 2006.
On average, OMI cloud fractions are higher by 0.011, and OMI cloud pressures exceed FRESCO cloud pressures by
60 hPa. A sequence of OMI observations over Europe in October 2005 shows OMI&apos;s capability to track
changeable NO&lt;sub&gt;x&lt;/sub&gt; air pollution from day to day in cloud-free situations.</abstract>
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