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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>8</volume_number>
		<issue_number>4</issue_number>
		<publication_year>2008</publication_year>
	</journal>
	<doi>10.5194/acpd-8-13847-2008</doi>
	<article_url>http://www.atmos-chem-phys-discuss.net/8/13847/2008/</article_url>
	<abstract_html>http://www.atmos-chem-phys-discuss.net/8/13847/2008/acpd-8-13847-2008.html</abstract_html>
	<fulltext_pdf>http://www.atmos-chem-phys-discuss.net/8/13847/2008/acpd-8-13847-2008.pdf</fulltext_pdf>
	<start_page>13847</start_page>
	<end_page>13901</end_page>
	<publication_date>2008-07-22</publication_date>
	<article_title content_type="html">Increasing ozone concentrations in marine boundary layer air inflow at the west coasts of North America and Europe</article_title>
	<authors>
		<author numeration="1" affiliations="1">
			<name>D. D. Parrish</name>
			<email>david.d.parrish@noaa.gov</email>
		</author>
		<author numeration="2" affiliations="2">
			<name>D. B. Millet</name>
		</author>
		<author numeration="3" affiliations="3">
			<name>A. H. Goldstein</name>
		</author>
	</authors>
	<affiliations>
		<affiliation numeration="1" content_type="html">NOAA Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway R/CSD7, Boulder, CO 80305 USA</affiliation>
		<affiliation numeration="2" content_type="html">Department of Soil, Water and Climate, University of Minnesota, St. Paul, MN, USA</affiliation>
		<affiliation numeration="3" content_type="html">Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA</affiliation>
	</affiliations>
	<abstract content_type="html">A rigorous method is presented for determining the ozone concentration in
the onshore flow of marine air at the North American west coast. By
combining the data available from all marine boundary layer sites with
simultaneous wind data, decadal temporal trends of MBL ozone concentrations
in all seasons are established with high precision. The average springtime
temporal trend over the past two decades is 0.46 ppbv/yr with a 95%
confidence limit of 0.13 ppbv/yr, and statistically significant trends are
found for all seasons except autumn, which does have a significantly smaller
trend than other seasons. The average trend in mean annual ozone
concentration is 0.34&amp;plusmn;0.09 ppbv/yr. These decadal trends at the North
American west coast present a striking comparison and contrast with the
trends reported for the European west coast at Mace Head, Ireland. The
trends in the winter, spring and summer seasons compare well at the two
locations, while the Mace Head trend is significantly greater in autumn.
Even though the trends are similar, the absolute ozone concentrations differ
markedly, with the marine air arriving at Europe in all seasons containing 7&amp;plusmn;2 ppbv
higher ozone concentrations than marine air arriving at North
America. Further, the ozone concentrations at the North American west coast
show no indication for stabilizing as has been reported for Mace Head. In a
larger historical context the background boundary layer ozone concentrations
over the 130 years covered by available data have increased substantially
(by a factor of two to three), and this increase continues at present, at
least in the marine boundary layer (MBL) of the Pacific coast region of
North America. The reproduction of the increasing trends in MBL ozone
concentrations over the past two decades as well as the difference in the
ozone concentrations between the two coastal regions will present a
significant challenge for global chemical transport models. Further, the
ability of the models to at least semi-quantitatively reproduce the
longer-term, historical trends may an even greater challenge.</abstract>
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