Wolfe, Glenn M. and Crounse, John D. and Parrish, Jonathan D. and St. Clair, Jason M. and Beaver, Melinda R. and Paulot, Fabien and Yoon, Tehshik P. and Wennberg, Paul O. and Keutsch, Frank N. (2012) Photolysis, OH reactivity and ozone reactivity of a proxy for isoprene-derived hydroperoxyenals (HPALDs). Physical Chemistry Chemical Physics, 14 (20). pp. 7276-7286. ISSN 1463-9076 http://resolver.caltech.edu/CaltechAUTHORS:20120530-085600230
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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 C_6-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) cm^3 molecule^(−1) s^(−1) at 296 K. The ozone reaction rate constant is (1.2 ± 0.2) × 10^(−18) cm^3 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 C_5-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 C_5-HPALD photo-oxidation products also photolyze to yield additional OH or if the C_5-HPALD production rate is faster than has been observed.
|Additional Information:||© 2012 Owner Societies. Received 08 Feb 2012, Accepted 28 Mar 2012. First published on the web 29 Mar 2012. This work was supported by the NOAA Climate and Global Change Postdoctoral Fellowship Program, administered by the University Corporation for Atmospheric Research. The authors thank NASA (NNX08AD29G), NSF (ATM-0934408 and ATM-0852406) and the Harvard University Center for the Environment for funding in support of this research. The authors also thank H. G. Kjaergaard for computation of ion-molecule collision rate parameters, M. Galloway for assistance with shipping logistics, and two anonymous reviewers for critical feedback on the manuscript.|
|Official Citation:||Photolysis, OH reactivity and ozone reactivity of a proxy for isoprene-derived hydroperoxyenals (HPALDs) Glenn M. Wolfe, John D. Crounse, Jonathan D. Parrish, Jason M. St. Clair, Melinda R. Beaver, Fabien Paulot, Tehshik P. Yoon, Paul O. Wennberg and Frank N. Keutsch Phys. Chem. Chem. Phys., 2012, 14, 7276-7286 DOI: 10.1039/C2CP40388A|
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|Deposited By:||Ruth Sustaita|
|Deposited On:||30 May 2012 16:29|
|Last Modified:||30 May 2012 16:29|
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