ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-4987-2009 A review of Secondary Organic Aerosol (SOA) formation from isoprene Carlton A. G. 1 Wiedinmyer C. 2 Kroll J. H. 3 4 US EPA, Office of Research and Development, Atmospheric Modeling and Analysis Division, Research Triangle Park, NC 27711, USA National Center for Atmospheric Research, Atmospheric Chemistry Division, Boulder, CO 80309, USA Aerodyne Research, Inc. 45 Manning Road, Billerica, MA 01821, USA currently at: Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 15 Vassar St. Bldg. 48–323, Cambridge, MA 02139, USA 27 07 2009 9 14 4987 5005 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/9/4987/2009/acp-9-4987-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/4987/2009/acp-9-4987-2009.pdf

Recent field and laboratory evidence indicates that the oxidation of isoprene, (2-methyl-1,3-butadiene, C<sub>5</sub>H<sub>8</sub>) forms secondary organic aerosol (SOA). Global biogenic emissions of isoprene (600 Tg yr<sup>&minus;1</sup>) are sufficiently large that the formation of SOA in even small yields results in substantial production of atmospheric particulate matter, likely having implications for air quality and climate. Here we present a review of field measurements, experimental work, and modeling studies aimed at understanding the mechanisms, yield, and atmospheric importance of isoprene-derived SOA. SOA yields depend on a number of factors, including organic aerosol loading (M<sub>o</sub>), NO<sub>x</sub> level (RO<sub>2</sub> chemistry), and, because of the importance of multigenerational chemistry, the degree of oxidation. These dependences are not always included in SOA modules used in atmospheric transport models, and instead most yield parameterizations rely on a single set of chamber experiments (carried out over a limited range of conditions); this may lead to very different estimates of the atmospheric importance of isoprene SOA. New yield parameterizations, based on all available laboratory data (M<sub>o</sub>=0–50 μg m<sup>&minus;3</sup>), are presented here, so that SOA formation may be computed as a function of M<sub>o</sub>, NO<sub>x</sub> level, and temperature. Current research needs and future research directions are identified.

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