Issue 20, 2012
From the journal:

Physical Chemistry Chemical Physics

Photolysis, OH reactivity and ozone reactivity of a proxy for isoprene-derived hydroperoxyenals (HPALDs)†

Glenn M. Wolfe,*a   John D. Crounse,b   Jonathan D. Parrish,a   Jason M. St. Clair,b   Melinda R. Beaver,bc   Fabien Paulot,d   Tehshik P. Yoon,a   Paul O. Wennbergbe  and  Frank N. Keutscha  

* Corresponding authors

a Department of Chemistry, University of Wisconsin, Madison, USA
E-mail: gwolfe@chem.wisc.edu

b Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, USA

c Now at National Exposure Research Laboratory, US EPA, Research Triangle Park, USA

d Division of Engineering and Applied Sciences, Harvard University, Cambridge, USA

e Division of Engineering and Applied Science, California Institute of Technology, Pasadena, USA

Abstract

The C5-hydroperoxyenals (C5-HPALDs) are a newly-recognized class of multi-functional hydrocarbons produced during the hydroxyl radical (OH)-initiated oxidation of isoprene. Recent theoretical calculations suggest that fast photolysis of these compounds may be an important OH source in high-isoprene, low-NO regions. We report experimental constraints for key parameters of photolysis, OH reaction and ozone reaction of these compounds as derived from a closely-related, custom-synthesized C6-HPALD. The photolysis quantum yield is 1.0 ± 0.4 over the range 300–400 nm, assuming an absorption cross section equal to the average of those measured for several analogous enals. The yield of OH from photolysis was determined as 1.0 ± 0.8. The OH reaction rate constant is (5.1 ± 1.8) × 10−11 cm3 molecule−1 s−1 at 296 K. The ozone reaction rate constant is (1.2 ± 0.2) × 10−18 cm3 molecule−1 s−1 at 296 K. These results are consistent with previous first-principles estimates, though the nature and fate of secondary oxidation products remains uncertain. Incorporation of C5-HPALD chemistry with the above parameters in a 0-D box model, along with experimentally-constrained rates for C5-HPALD production from isomerization of first-generation isoprene hydroxyperoxy radicals, is found to enhance modeled OH concentrations by 5–16% relative to the traditional isoprene oxidation mechanism for the chemical regimes of recent observational studies in rural and remote regions. This enhancement in OH will increase if C5-HPALD photo-oxidation products also photolyze to yield additional OH or if the C5-HPALD production rate is faster than has been observed.

Graphical abstract: Photolysis, OH reactivity and ozone reactivity of a proxy for isoprene-derived hydroperoxyenals (HPALDs)

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Article information

DOI
https://doi.org/10.1039/C2CP40388A
Article type
Paper
Submitted
08 Feb 2012
Accepted
28 Mar 2012
First published
29 Mar 2012

Phys. Chem. Chem. Phys., 2012,14, 7276-7286

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Photolysis, OH reactivity and ozone reactivity of a proxy for isoprene-derived hydroperoxyenals (HPALDs)

G. M. Wolfe, J. D. Crounse, J. D. Parrish, J. M. St. Clair, M. R. Beaver, F. Paulot, T. P. Yoon, P. O. Wennberg and F. N. Keutsch, Phys. Chem. Chem. Phys., 2012, 14, 7276 DOI: 10.1039/C2CP40388A

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