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Published February 23, 2009 | Published
Journal Article Open

Isoprene photooxidation : new insights into the production of acids and organic nitrates


We describe a nearly explicit chemical mechanism for isoprene photooxidation guided by chamber studies that include time-resolved observation of an extensive suite of volatile compounds. We provide new constraints on the chemistry of the poorly-understood isoprene δ-hydroxy channels, which account for more than one third of the total isoprene carbon flux and a larger fraction of the nitrate yields. We show that the cis branch dominates the chemistry of the δ-hydroxy channel with less than 5% of the carbon following the trans branch. The modelled yield of isoprene nitrates is 12±3% with a large difference between the δ and β branches. The oxidation of these nitrates releases about 50% of the NOx. Methacrolein nitrates (modelled yield ≃15±3% from methacrolein) and methylvinylketone nitrates (modelled yield ≃11±3% yield from methylvinylketone) are also observed. Propanone nitrate, produced with a yield of 1% from isoprene, appears to be the longest-lived nitrate formed in the total oxidation of isoprene. We find a large molar yield of formic acid and suggest a novel mechanism leading to its formation from the organic nitrates. Finally, the most important features of this mechanism are summarized in a condensed scheme appropriate for use in global chemical transport models.

Additional Information

© Author(s) 2009. This work is distributed under the Creative Commons Attribution 3.0 License. Received: 10 June 2008 – Published in Atmos. Chem. Phys. Discuss.: 31 July 2008. Revised: 4 February 2009 – Accepted: 4 February 2009 – Published: 23 February 2009. The authors wish to thank T. S. Dibble, D. Taraborrelli and an anonymous referee for their helpful comments on the initial manuscript. F. Paulot wishes to thank C. D. Vecitis for helpful discussions regarding chemical mechanisms. This study was supported by the National Science Foundation (NSF) under grant ATM-0432377, by the US Department of Energy under grant DE-FG02-05ER63983, by US Environmental Protection Agency under grant RD-83374901 and by the Marsden Fund administrated by the Royal Society of New Zealand. F. Paulot is supported by the William and Sonya Davidow graduate fellowship. J. D. Crounse thanks the EPA-STAR Fellowship Program (FP916334012) for providing support. This work has not been formally reviewed by the EPA. The views expressed in this document are solely those of the authors and the EPA does not endorse any products or commercial services mentioned in this publication.

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