Gas-phase ozonolysis of trans-2-hexenal: Kinetics, products, mechanism and SOA formation

International audienceIn this work, kinetics, product formation, chemical mechanism and SOA formation for the gas-phase reaction of trans-2-hexenal (T2H) with O3 are examined using four complementary experimental setups at 298 ± 2 K and atmospheric pressure. Product studies were conducted in two contrasted experimental conditions, with and without OH radical scavenger. The ozonolysis rate constant was determined in both static and dynamic reactors. An average reaction rate constant of (1.52 ± 0.19) × 10−18 cm3 molecule−1 s−1 was determined. Glyoxal and butanal were identified as main products with molar yields of 59 ± 15% and 36 ± 9%, respectively, in the presence of an OH scavenger. Slightly lower values were obtained in the absence of scavenger. Acetaldehyde, propanal and 2-hydroxybutanal were also identified and quantified. A reaction mechanism was proposed based on the observed products. SOA formation was observed with aerosol mass yields andgt;13% for SOA masses of 400 μg m−3. This work demonstrates for the first time that 2-alkenals ozonolysis can be a source of SOA in the atmosphere

Experimental and Theoretical Studies of Trans-2-Pentenal Atmospheric Ozonolysis

International audienceWe investigated the kinetics, mechanism and secondary organic aerosols formation of the ozonolysis of trans-2-pentenal (T2P) using four different reactors with Fourier Transform InfraRed (FTIR) spectroscopy and Gas Chromatography (GC) techniques at T = 298 ± 2 K and 760 Torr in dry conditions. The rate coefficients and branching ratios were also evaluated using the canonical vari-ational transition (CVT) state theory coupled with small curvature tunneling (CVT/SCT) in the range 278–350 K. The experimental rate coefficient at 298 K was (1.46 ± 0.17) × 10−18 cm3 molecule−1 s−1, in good agreement with the theoretical rate. The two primary carbonyls formation yields, gly-oxal and propanal, were 57 ± 10% and 42 ± 12%, respectively, with OH scavenger compared to 38 ± 8% for glyoxal and 26 ± 5% for propanal without OH scavenger. Acetaldehyde and 2-hydroxypro-panal were also identified and quantified with yields of 9 ± 3% and 5 ± 2%, respectively, in the presence of OH scavenger. For the OH production, an upper limit of 24% was estimated using me-sitylene as OH tracer. Combining experimental and theoretical findings enabled the establishment of a chemical mechanism. Finally, the SOA formation was observed with mass yields of about 1.5%. This work provides additional information on the effect of the aldehyde functional group on the fragmentation of the primary ozonide. © 2022 by the authors. Licensee MDPI, Basel, Switzerland