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- ItemFirst oxidation products from the reaction of hydroxyl radicals with isoprene for pristine environmental conditions([London] : Macmillan Publishers Limited, part of Springer Nature, 2019) Berndt, Torsten; Hyttinen, Noora; Herrmann, Hartmut; Hansel, ArminIsoprene, C5H8, inserts about half of the non-methane carbon flux of biogenic origin into the atmosphere. Its degradation is primarily initiated by the reaction with hydroxyl radicals. Here we show experimentally the formation of reactive intermediates and corresponding closed-shell products from the reaction of hydroxyl radicals with isoprene for low nitric oxide and low hydroperoxy radical conditions. Detailed product analysis is achieved by mass spectrometric techniques. Quantum chemical calculations support the usefulness of applied ionization schemes. Observed peroxy radicals are the isomeric HO-C5H8O2 radicals and their isomerization products HO-C5H8(O2)O2, bearing most likely an additional hydroperoxy group, and in traces HO-C5H8(O2)2O2 with two hydroperoxy groups. Main closed-shell products from unimolecular peroxy radical reactions are hydroperoxy aldehydes, C5H8O3, and smaller yield products with the composition C5H8O4 and C4H8O5. Detected signals of C10H18O4, C10H18O6, and C5H10O2 stand for products arising from peroxy radical self- and cross-reactions. © 2019, The Author(s).
- ItemEfficient alkane oxidation under combustion engine and atmospheric conditions([London] : Macmillan Publishers Limited, part of Springer Nature, 2021) Wang, Zhandong; Ehn, Mikael; Rissanen, Matti P.; Garmash, Olga; Quéléver, Lauriane; Xing, Lili; Monge-Palacios, Manuel; Rantala, Pekka; Donahue, Neil M.; Berndt, Torsten; Sarathy, S. ManiOxidation chemistry controls both combustion processes and the atmospheric transformation of volatile emissions. In combustion engines, radical species undergo isomerization reactions that allow fast addition of O2. This chain reaction, termed autoxidation, is enabled by high engine temperatures, but has recently been also identified as an important source for highly oxygenated species in the atmosphere, forming organic aerosol. Conventional knowledge suggests that atmospheric autoxidation requires suitable structural features, like double bonds or oxygen-containing moieties, in the precursors. With neither of these functionalities, alkanes, the primary fuel type in combustion engines and an important class of urban trace gases, are thought to have minor susceptibility to extensive autoxidation. Here, utilizing state-of-the-art mass spectrometry, measuring both radicals and oxidation products, we show that alkanes undergo autoxidation much more efficiently than previously thought, both under atmospheric and combustion conditions. Even at high concentrations of NOX, which typically rapidly terminates autoxidation in urban areas, the studied C6–C10 alkanes produce considerable amounts of highly oxygenated products that can contribute to urban organic aerosol. The results of this inter-disciplinary effort provide crucial information on oxidation processes in both combustion engines and the atmosphere, with direct implications for engine efficiency and urban air quality.