Ozonolysis of α-Pinene and Δ 3 -Carene Mixtures: Formation of Dimers with Two Precursors

• Published in: Environmental science & technology 2022-12, Vol.56 (23), p.16643-16651
• Main Authors: Thomsen, Ditte, Thomsen, Lotte Dyrholm, Iversen, Emil Mark, Björgvinsdóttir, Thuríđur Nótt, Vinther, Sofie Falk, Skønager, Jane Tygesen, Hoffmann, Thorsten, Elm, Jonas, Bilde, Merete, Glasius, Marianne
• Format: Article
• Language: English
• Subjects: Aerosols - chemistry; Air Pollutants - chemistry; Humans; Monoterpenes - chemistry; Ozone - chemistry; Volatile Organic Compounds - chemistry
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.2c04786

The formation of secondary organic aerosol (SOA) from the structurally similar monoterpenes, α-pinene and Δ -carene, differs substantially. The aerosol phase is already complex for a single precursor, and when mixtures are oxidized, products, e.g., dimers, may form between different volatile organic compounds (VOCs). This work investigates whether differences in SOA formation and properties from the oxidation of individual monoterpenes persist when a mixture of the monoterpenes is oxidized. Ozonolysis of α-pinene, Δ -carene, and a 1:1 mixture of them was performed in the Aarhus University Research on Aerosol (AURA) atmospheric simulation chamber. Here, ∼100 ppb of monoterpene was oxidized by 200 ppb O under dark conditions at 20 °C. The particle number concentration and particle mass concentration for ozonolysis of α-pinene exceed those from ozonolysis of Δ -carene alone, while their mixture results in concentrations similar to α-pinene ozonolysis. Detailed offline analysis reveals evidence of VOC-cross-product dimers in SOA from ozonolysis of the monoterpene mixture: a VOC-cross-product dimer likely composed of the monomeric units -caric acid and 10-hydroxy-pinonic acid and a VOC-cross-product dimer ester likely from the monomeric units caronaldehyde and terpenylic acid were tentatively identified by liquid chromatography-mass spectrometry. To improve the understanding of chemical mechanisms determining SOA, it is relevant to identify VOC-cross-products.