Extended Data Figure 9: Schematic illustrations of ELVOC formation.

a, Internal hydrogen abstraction by an RO₂ (‘H-shift’), followed by oxygen addition at the alkyl radical site, forming a more oxidized peroxy radical. Depending on the exact structure of the molecule, this new RO₂ can perform subsequent H-shifts/O₂-additions to increase the oxygen content even further. b, c, Simplified diagram of ELVOC formation. The general form is shown in b, and a specific example pathway from α-pinene (C₁₀H₁₆) ozonolysis in c. For clarity, all reactions not leading to ELVOCs are omitted. The first reaction yields a peroxy radical (b: RO₂, c: C₁₀H₁₅O₄^•), that can undergo several fast H-shift reactions followed by O₂-addition, resulting in more oxidized peroxy radicals (b: R_ELVOCO₂, c: C₁₀H₁₅O₁₀^•). R_ELVOCO₂ can react through well-established pathways with either HO₂, RO₂ or NO, all of which can form ELVOCs. The relative abundance of these species as well as the rates of the unimolecular decomposition reactions determines the overall ELVOC mass yield, while not necessarily affecting the molar yield. Only reactions of R_ELVOCO₂ with other RO₂ can form dimers (R_ELVOCOOR), whereas organic nitrates (R_ELVOCONO₂) only form in reactions with NO. All compounds in bold font were directly measured.