Gas-Phase Ozone Reaction Kinetics of C5-C8 Unsaturated Alcohols of Biogenic Interest

Unsaturated alcohols are volatile organic compounds (VOCs) that characterize the emissions of plants. Changes in climate together with related increases of biotic and abiotic stresses are expected to increase these emissions in the future. Ozonolysis is one of the oxidation pathways that control the fate of unsaturated alcohols in the atmosphere. The rate coefficients of the gas-phase O₃ reaction with seven C₅-C₈ unsaturated alcohols were determined at 296 K using both absolute and relative kinetic methods. The following rate coefficients (cm³ molecule^-1 s^-1) were obtained using the absolute method: (1.1 ± 0.2) × 10^-16 for cis-2-penten-1-ol, (1.2 ± 0.2) × 10^-16 for trans-2-hexen-1-ol, (6.4 ± 1.0) × 10^-17 for trans-3-hexen-1-ol, (5.8 ± 0.9) × 10^-17 for cis-3-hexen-1-ol, (2.0 ± 0.3) × 10^-17 for 1-octen-3-ol, and (8.4 ± 1.3) × 10^-17 for trans-2-octen-1-ol. The following rate coefficients (cm³ molecule^-1 s^-1) were obtained using the relative method: (1.27 ± 0.11) × 10^-16 for trans-2-hexen-1-ol, (5.01 ± 0.30) × 10^-17 for trans-3-hexen-1-ol, (4.13 ± 0.34) × 10^-17 for cis-3-hexen-1-ol, and (1.40 ± 0.12) × 10^-16 for trans-4-hexen-1-ol. Alkenols display high reactivities with ozone with lifetimes in the hour range. Rate coefficients show a strong and complex dependence on the structure of the alkenol, particularly the relative position of the OH group toward the C═C double bond. The results are discussed and compared to both the available literature data and four structure-activity relationship (SAR) methods.

Iodide Accelerates the Processing of Biogenic Monoterpene Emissions on Marine Aerosols

Marine photosynthetic organisms emit organic gases, including the polyolefins isoprene (C₅H₈) and monoterpenes (MTPs, C₁₀H₁₆), into the boundary layer. Their atmospheric processing produces particles that influence cloud formation and growth and, as a result, the Earth's radiation balance. Here, we report that the heterogeneous ozonolysis of dissolved α-pinene by O₃(g) on aqueous surfaces is dramatically accelerated by I^-, an anion enriched in the ocean upper microlayer and sea spray aerosols (SSAs). In our experiments, liquid microjets of α-pinene solutions, with and without added I^-, are dosed with O₃(g) for τ < 10 μs and analyzed online by pneumatic ionization mass spectrometry. In the absence of I^-, α-pinene does not detectably react with O₃(g) under present conditions. In the presence of ≥ 0.01 mM I^-, in contrast, new signals appear at m/z = 169 (C₉H₁₃O₃ ^-), m/z = 183 (C₁₀H₁₅O₃ ^-), m/z = 199 (C₁₀H₁₅O₄ ^-), m/z = 311 (C₁₀H₁₆IO₃ ^-), and m/z = 461 (C₂₀H₃₀IO₄ ^-), plus m/z = 175 (IO₃ ^-), and m/z = 381 (I₃ ^-). Collisional fragmentation splits CO₂ from C₉H₁₃O₃ ^-, C₁₀H₁₅O₃ ^- and C₁₀H₁₅O₄ ^-, and I^- plus IO^- from C₁₀H₁₆IO₃ ^- as expected from a trioxide IOOO^•C₁₀H₁₆ ^- structure. We infer that the oxidative processing of α-pinene on aqueous surfaces is significantly accelerated by I^- via the formation of IOOO^- intermediates that are more reactive than O₃. A mechanism in which IOOO^- reacts with α-pinene (and likely with other unsaturated species) in competition with its isomerization to IO₃ ^- accounts for present results and the fact that soluble iodine in SSA is mostly present as iodine-containing organic species rather than the thermodynamically more stable iodate. By this process, a significant fraction of biogenic MTPs and other unsaturated gases may be converted to water-soluble species rather than emitted to the atmosphere.

Kinetic and mechanistic study on gas phase reactions of ozone with a series ofcis-3-hexenyl esters

Reaction kinetics of O₃with fourcis-3-hexenyl esters were studied using experimental methods in a flow tube reactor as well as using theoretical methods.