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OH Radical-Initiated Chemistry of Isoprene in Aqueous Media. Atmospheric Implications

Kameel, F. Rifkha and Hoffmann, M. R. and Colussi, A. J. (2013) OH Radical-Initiated Chemistry of Isoprene in Aqueous Media. Atmospheric Implications. Journal of Physical Chemistry A, 117 (24). pp. 5117-5123. ISSN 1089-5639.

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The fate of isoprene (2-methyl-1,3-butadiene, ISO) emissions into the atmosphere is not fully understood. Increasing awareness that ISO is only partially processed in the gas-phase has turned attention to its reactive uptake by fog, cloud, and aerosol droplets. A hydrophobic gas, ISO would preferentially partition to the surface rather than the bulk of aqueous media. Such media normally contain dissolved O_2 and water-soluble unsaturated organics and support •OH generation rates (from the solar photolysis of dissolved H_(2)O_2) that are several orders of magnitude larger than in the gas-phase. Thus, ISO should be converted therein to heavier products rather than into the C_4–C_5 volatile compounds produced in the gas-phase. Here we substantiate such a scenario by reporting that the λ > 305 nm photolysis of H_(2)O_2 in dilute aqueous ISO solutions yields C_(10)H_(15)OH species as primary products, whose formation both requires and is inhibited by O_2. A minimum of seven C_(10)H_(15)OH isomers are resolved by reverse-phase high-performance liquid chromatography and detected as MH^+ (m/z = 153) and MH^(+)-18 (m/z = 135) signals by electrospray ionization mass spectrometry. Our findings are consistent with the addition of •OH to ISO, followed by HO-ISO• reactions with ISO in competition with O_2, leading to second generation HO(ISO)_2• radicals that terminate as C_(10)H_(15)OH via β-H abstraction by O_2. We show that a significant fraction of gas-phase olefins should be converted into less volatile species via this process on wet airborne particles.

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Hoffmann, M. R.0000-0001-6495-1946
Colussi, A. J.0000-0002-3400-4101
Additional Information:© 2013 American Chemical Society. Received: March 15, 2013; Revised: May 20, 2013; Published: May 22, 2013. This work was supported by NSF (U.S.A.) Grant AC-1238977.
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Issue or Number:24
Record Number:CaltechAUTHORS:20130814-142242191
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Official Citation:OH Radical-Initiated Chemistry of Isoprene in Aqueous Media. Atmospheric Implications F. Rifkha Kameel, M. R. Hoffmann, and A. J. Colussi The Journal of Physical Chemistry A 2013 117 (24), 5117-5123
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39917
Deposited By: Jason Perez
Deposited On:15 Aug 2013 14:07
Last Modified:03 Mar 2020 13:01

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