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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>6</issue_number>
		<publication_year>2008</publication_year>
	</journal>
	<doi>10.5194/acpd-8-19891-2008</doi>
	<article_url>http://www.atmos-chem-phys-discuss.net/8/19891/2008/</article_url>
	<abstract_html>http://www.atmos-chem-phys-discuss.net/8/19891/2008/acpd-8-19891-2008.html</abstract_html>
	<fulltext_pdf>http://www.atmos-chem-phys-discuss.net/8/19891/2008/acpd-8-19891-2008.pdf</fulltext_pdf>
	<start_page>19891</start_page>
	<end_page>19916</end_page>
	<publication_date>2008-11-28</publication_date>
	<article_title content_type="html">The CO&lt;sub&gt;2&lt;/sub&gt; inhibition of terrestrial isoprene emission significantly affects future ozone projections</article_title>
	<authors>
		<author numeration="1" affiliations="1,2,4">
			<name>P. J. Young</name>
			<email>paul.j.young@noaa.gov</email>
		</author>
		<author numeration="2" affiliations="3">
			<name>A. Arneth</name>
		</author>
		<author numeration="3" affiliations="3">
			<name>G. Schurgers</name>
		</author>
		<author numeration="4" affiliations="1,2">
			<name>G. Zeng</name>
		</author>
		<author numeration="5" affiliations="1,2">
			<name>J. A. Pyle</name>
		</author>
	</authors>
	<affiliations>
		<affiliation numeration="1" content_type="html">Centre for Atmospheric Science, Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UK</affiliation>
		<affiliation numeration="2" content_type="html">National Centre for Atmospheric Science, UK</affiliation>
		<affiliation numeration="3" content_type="html">Department of Physical Geography and Ecosystems Analysis, Centre for GeoBiosphere Science, Lund University, Sölvegatan, Lund, Sweden</affiliation>
		<affiliation numeration="4" content_type="html">now at: NOAA/ESRL, 325 Broadway, Boulder, CO 80 305, USA</affiliation>
	</affiliations>
	<abstract content_type="html">Simulations of future tropospheric composition often include substantial
increases in biogenic isoprene emissions arising from the Arrhenius-like leaf
emission response and warmer surface temperatures, and from enhanced
vegetation productivity in response to temperature and atmospheric CO&lt;sub&gt;2&lt;/sub&gt;
concentration. However, a number of recent laboratory and field data have
suggested a direct inhibition of leaf isoprene production by increasing
atmospheric CO&lt;sub&gt;2&lt;/sub&gt; concentration, notwithstanding isoprene being produced
from precursor molecules that include some of the primary products of carbon
assimilation. The cellular mechanism that underlies the decoupling of leaf
photosynthesis and isoprene production still awaits a full explanation but
accounting for this observation in a dynamic vegetation model that contains a
semi-mechanistic treatment of isoprene emissions has been shown to change
future global isoprene emission estimates notably. Here we use these
estimates in conjunction with a chemistry-climate model to compare the
effects of isoprene simulations without and with a direct CO&lt;sub&gt;2&lt;/sub&gt;-inhibition
on late 21st century O&lt;sub&gt;3&lt;/sub&gt; and OH levels. The impact on surface O&lt;sub&gt;3&lt;/sub&gt; was
significant. Including the CO&lt;sub&gt;2&lt;/sub&gt;-inhibition of isoprene resulted in opposing
responses in polluted (O&lt;sub&gt;3&lt;/sub&gt; decreases of up to 10 ppbv) vs. less polluted
(O&lt;sub&gt;3&lt;/sub&gt; increases of up to 10 ppbv) source regions, due to isoprene nitrate
and peroxy acetyl nitrate (PAN) chemistry. OH concentration increased with
relatively lower future isoprene emissions, decreasing methane lifetime by
~7 months. Our simulations underline the large uncertainties in
future chemistry and climate studies due to biogenic emission patterns and
emphasize the problems of using globally averaged climate metrics to quantify
the atmospheric impact of reactive, heterogeneously distributed substances.</abstract>
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