Aqueous-phase photo-oxidation of selected green leaf volatiles initiated by OH radicals: Products and atmospheric implications

Kumar Sarang; Tobias Otto; Sahir Gagan; Krzysztof Rudzinski; Thomas Schaefer; Martin Brüggemann; Irena Grgić; Adam Kubas; Hartmut Herrmann; Rafal Szmigielski

doi:10.1016/j.scitotenv.2023.162622

Aqueous-phase photo-oxidation of selected green leaf volatiles initiated by OH radicals: Products and atmospheric implications

Sci Total Environ. 2023 Jun 25:879:162622. doi: 10.1016/j.scitotenv.2023.162622. Epub 2023 Mar 5.

Authors

Affiliations

¹ Institute of Physical Chemistry Polish Academy of Sciences, 01-224 Warsaw, Poland.
² Atmospheric Chemistry Department (ACD), Leibniz Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany.
³ Department of Analytical Chemistry, National Institute of Chemistry, SI-1000 Ljubljana, Slovenia.
⁴ Institute of Physical Chemistry Polish Academy of Sciences, 01-224 Warsaw, Poland. Electronic address: akubas@ichf.edu.pl.
⁵ Atmospheric Chemistry Department (ACD), Leibniz Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany. Electronic address: herrmann@tropos.de.
⁶ Institute of Physical Chemistry Polish Academy of Sciences, 01-224 Warsaw, Poland. Electronic address: ralf@ichf.edu.pl.

Abstract

C₅- and C₆- unsaturated oxygenated organic compounds emitted by plants under stress like cutting, freezing or drying, known as Green Leaf Volatiles (GLVs), may clear some of the existing uncertainties in secondary organic aerosol (SOA) budget. The transformations of GLVs are a potential source of SOA components through photo-oxidation processes occurring in the atmospheric aqueous phase. Here, we investigated the aqueous photo-oxidation products from three abundant GLVs (1-penten-3-ol, (Z)-2-hexen-1-ol, and (E)-2-hexen-1-al) induced by OH radicals, carried out in a photo-reactor under simulated solar conditions. The aqueous reaction samples were analyzed using advanced hyphenated mass spectrometry techniques: capillary gas chromatography mass spectrometry (c-GC-MS); and reversed-phase liquid chromatography high resolution mass spectrometry (LC-HRMS). Using carbonyl-targeted c-GC-MS analysis, we confirmed the presence of propionaldehyde, butyraldehyde, 1-penten-3-one, and 2-hexen-1-al in the reaction samples. The LC-HRMS analysis confirmed the presence of a new carbonyl product with the molecular formula C₆H₁₀O₂, which probably bears the hydroxyhexenal or hydroxyhexenone structure. Density functional theory (DFT)-based quantum calculations were used to evaluate the experimental data and obtain insight into the formation mechanism and structures of the identified oxidation products via the addition and hydrogen-abstraction pathways. DFT calculations highlighted the importance of the hydrogen abstraction pathway leading to the new product C₆H₁₀O₂. Atmospheric relevance of the identified products was evaluated using a set of physical property data like Henry's law constant (HLC) and vapor pressure (VP). The unknown product of molecular formula C₆H₁₀O₂ has higher HLC and lower VP than the parent GLV and thus has potential to remain in the aqueous phase leading to possible aqueous SOA formation. Other observed carbonyl products are likely first stage oxidation products and precursors of aged SOA.

Keywords: Aqueous phase; DFT calculations; Green leaf volatiles; Hydroxyl radicals; Reaction products; Secondary organic aerosol.