Seminar

Abstract

Biogenic emissions by vegetation contribute to the vast majority of the volatile organic compounds (VOC) present in the atmosphere. As such, understanding their oxidation pathways is important to determine their eventual impact on the production of secondary pollutants and particles. Many of these oxidation processes are initiated by the hydroxyl radical (OH) which plays an important role in removing pollutants during the daytime. Studies on isoprene oxidation by OH radicals highlighted that, in pristine environments despite low nitrogen oxide (NO) levels, relatively high concentrations of OH radicals can be sustained. This is due to isomerization reactions of peroxy radicals (RO2) which become important at low NO concentrations since they recycle the OH radical efficiently. These reactions have been experimentally investigated for isoprene but limited studies are available for different biogenic VOCs (BVOCs); however, theoretical work suggests that isomerization reactions can be an important loss path for a wide range of RO2 radicals.

Photo-oxidation experiments on a series of BVOCs (α- and β-pinene, methyl vinyl ketone, methacrolein, 2-methyl-3-butene-2-ol and isoprene) were performed in the atmospheric simulation chamber SAPHIR at the Forschungszentrum Jülich. This simulation chamber allows for studying the degradation of the BVOCs at atmospheric conditions with the use of sunlight in a controlled environment. Measurements at the chamber include radical species (OH, HO2 and RO2), BVOCs and oxygenated VOCs (OVOCs), inorganic trace gases and solar radiation. Planning and evaluation of the experiments was supported by quantum-chemical calculations highlighting possible new reaction pathways. Radical and trace gas measurements were compared to model calculations using the latest version of the Master Chemical Mechanism with the inclusion of new reaction pathways as described in literature or derived from quantum chemical calculations focusing on the importance of RO2 radical isomerization reactions for the HOx radical (OH + HO2) budget.

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Anna Novelli is a research scientist at the Forschungszentrum Juelich. She received her PhD from the University of Turin, where she studied Criegee intermediates and their role in atmospheric oxidation. Her current research focuses on radicals species and their interactions with biogenic emissions.