Aqueous-Phase Decomposition of Isoprene Hydroxy Hydroperoxide and Hydroxyl Radical Formation by Fenton-like Reactions with Iron Ions

Ting Fang; Pascale S J Lakey; Jean C Rivera-Rios; Frank N Keutsch; Manabu Shiraiwa

doi:10.1021/acs.jpca.0c02094

Aqueous-Phase Decomposition of Isoprene Hydroxy Hydroperoxide and Hydroxyl Radical Formation by Fenton-like Reactions with Iron Ions

J Phys Chem A. 2020 Jun 25;124(25):5230-5236. doi: 10.1021/acs.jpca.0c02094. Epub 2020 Jun 16.

Authors

Ting Fang¹, Pascale S J Lakey¹, Jean C Rivera-Rios², Frank N Keutsch^{2

3}, Manabu Shiraiwa¹

Affiliations

¹ Department of Chemistry, University of California, Irvine, California 92697, United States.
² Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, United States.
³ Harvard John A. Paulson School of Engineering and Applied Sciences, Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, United States.

PMID: 32479080
DOI: 10.1021/acs.jpca.0c02094

Abstract

Isoprene hydroxy hydroperoxides (ISOPOOH) formed by the photooxidation of isoprene under low-NO conditions play an important role in the formation and evolution of secondary organic aerosols, yet multiphase processes of ISOPOOH are poorly understood. By applying electron paramagnetic resonance spectroscopy, we observe that ISOPOOH undergoes aqueous-phase decomposition upon interacting with Fe(II) ions to form OH and organic radicals at room temperature. To reproduce the measured dependence of OH formation on the Fe concentrations by kinetic modeling, we postulate that Fe(II) ions react with ISOPOOH via Fenton-like reactions to form OH radicals with a rate constant of 7.3 × 10^-18 cm³ s^-1. At low concentrations, oxalate forms monocomplexes with Fe(II) ions, which can promote OH formation by ISOPOOH. However, at high concentrations, oxalate scavenges OH radicals, thereby lowering aqueous OH concentrations. These findings provide new insight for the atmospheric fate of ISOPOOH and reactive oxygen species generation in the aqueous phase.