Reactions of NO₃ with aromatic aldehydes: gas-phase kinetics and insights into the mechanism of the reaction

Rate coefficients for the reaction of NO3 radicals with a series of aromatic aldehydes were measured in a 7300 L simulation chamber at ambient temperature and pressure by relative and absolute methods. The rate coefficients for benzaldehyde (BA), ortho-tolualdehyde (O-TA), meta-tolualdehyde (M-TA), para-tolualdehyde (P-TA), 2,4-dimethyl benzaldehyde (2,4-DMBA), 2,5-dimethyl benzaldehyde (2,5-DMBA) and 3,5-dimethyl benzaldehyde (3,5-DMBA) were k1= 2.6 ± 0.3, k2= 8.7 ± 0.8, k3= 4.9 ± 0.5, k4= 4.9 ± 0.4, k5= 15.1 ± 1.3, k6= 12.8 ± 1.2 and k7= 6.2 ± 0.6, respectively, in the units of 10−15 cm3 molec.−1 s−1 at 298 ± 2 K. The rate coefficient k13 for the reaction of the NO3 radical with deuterated benzaldehyde (benzaldehyde-d1) was found to be half that of k1. The end product of the reaction in an excess of NO2 was measured to be C6H5C(O)O2NO2. Theoretical calculations of aldehydic bond energies and reaction pathways indicate that the NO3 radical reacts primarily with aromatic aldehydes through the abstraction of an aldehydic hydrogen atom. The atmospheric implications of the measured rate coefficients are briefly discussed.

Reactions of NO₃ with Aromatic Aldehydes: Gas Phase Kinetics and Insights into the Mechanism of the Reaction

Rate coefficients for the reaction of NO3 radicals with a series of aromatic aldehydes were measured in a 7300 liter simulation chamber at ambient temperature and pressure by relative and absolute methods. The rate coefficients for benzaldehyde (BA), ortho-tolualdehyde (O-TA), meta-tolualdehyde (M-TA), para-tolualdehyde (P-TA), 2,4-dimethyl benzaldehyde (2,4-DMBA), 2,5-dimethyl benzaldehyde (2,5-DMBA) and 3,5-dimethyl benzaldehyde (3,5-DMBA) were: k1 = 2.6 ± 0.3, k2 = 8.8 ± 0.8, k3 = 4.8 ± 0.5, k4 = 4.9 ± 0.5, k5 = 15.1 ± 1.4, k6 = 12.7 ± 1.2 and k7 = 6.2 ± 0.6, respectively, in the units of 10−15 cm3 molecule−1 s−1 at 298 ± 2 K. The rate coefficient k13 for the reaction of the NO3 radical with deuterated benzaldehyde (benzaldehyde-d1) was found to be half that of k1. The end product of the reaction with an excess of NOx was measured to be C6H5C(O)O2NO2. Theoretical calculations of aldehydic bond energies and reaction pathways indicate that NO3 radical reacts with aromatic aldehydes through the abstraction of aldehydic hydrogen atom. The atmospheric implications of the measured rate coefficients are briefly discussed.

Study of the tropospheric degradation of 2-methylbutanal initiated by OH radicals, Cl atoms and sunlight

<p>The biogenic oxygenated volatile compound 2-methylbutanal (2MB) is emitted into the low atmosphere from several natural sources such as microbiological processes, wildland fires, or emissions from vegetation<sup>1</sup>. Moreover, some industrial operations also generate 2MB<sup>2</sup>. During the day, the oxidation of 2MB can be initiated by sunlight, hydroxyl (OH) radicals or chlorine (Cl) atoms in marine atmospheres. Up to date, gas-phase kinetics of OH with 2MB has only been studied at room temperature<sup>3</sup>. The photolysis rate coefficients (<em>J</em>) of 2MB initiated by sunlight have also been reported<sup>4</sup>. However, there is no available data for the reaction of Cl atoms with 2MB and the photolysis products.</p><p>In this work, the photolysis rate coefficient (<em>J</em>) of 2MB has been measured using a solar simulator in a Pyrex cell coupled to a Fourier Transform Infrared (FTIR) spectrometer to monitor the loss of 2MB. Moreover, the gas-phase kinetics of the reaction of 2MB with Cl (<em>k</em><sub>Cl</sub>) and OH (<em>k</em><sub>OH</sub>) have been investigated to evaluate the contribution of these homogeneous degradation routes to the total loss of 2MB in the atmosphere. All the kinetic experiments were carried out under free-NO<sub>x</sub> conditions (simulating a clean atmosphere). Regarding the relative kinetic study on the Cl-reaction, an atmospheric simulation chamber coupled to a FTIR spectrometer was used at 298 K and 760 Torr <sup>5</sup> of air, whereas for the absolute kinetics of the OH-reaction, <em>k</em><sub>OH</sub> was determined as a function of temperature and pressure (T = 263-353 K and P = 50-600 Torr of helium) by using a pulsed laser photolysis-laser induced fluorescence system<sup>6</sup>. Finally, in addition to FTIR, gas chromatography coupled to mass spectrometry and proton transfer time-of-flight mass spectrometry were used to detect the gas-phase reaction products when 2MB was exposed to Cl and sunlight. The atmospheric implications will be discussed in terms of lifetimes and reactions products.</p><p><strong>REFERENCES:</strong> <strong>1</strong>. Szwajkowska-Michale, L., Busko, M., Lakomy, P., and Perkowski, J.: Determination of profiles of volatile metabolites produced by Trametes versicolor isolates antagonistic towards Armillaria spp. Sylwan. <strong>2018</strong>, 162, 499–508. <strong>2. </strong>Kolar, P.; Kastner, J. R. Low-Temperature Catalytic Oxidation of Aldehyde Mixtures Using Wood Fly Ash: Kinetics, Mechanism, and Effect of Ozone. Chemosphere. <strong>2010</strong>, 78 (9), 1110–1115. <strong>3. </strong>D’Anna, B.; Andresen, O.; Gefen, Z. and Nielsen, C.J.: Kinetic study of OH and NO<sub>3</sub> radical reactions with 14 aliphatic aldehydes. Phys.Chem.Chem.Phys. <strong>2001</strong>, 3, 3057-3063. <strong>4. </strong>Wenger, J.C.: Chamber Studies on the Photolysis of Aldehydes. Environmental Simulation Chambers: Application to Atmospheric Chemical Processes. <strong>2006. </strong>Nato Science Series: IV: Earth and Environmental Science, vol 62. Springer, Dordrecht. <strong>5. </strong>Antiñolo, M.; Asensio, M.; Albadalejo, J. and Jiménez E.: Gas-Phase Reaction of trans-2-methyl-2-butenal with Cl: Kinetics, Gaseous Products, and SOA Formation. Atmosphere <strong>2020</strong>, 11 (7), 715. <strong>6. </strong>Blázquez, S.; Antiñolo, M.; Nielsen, O. J.; Albadalejo, J. and Jiménez, E.: Reaction kinetics of (CF<sub>3</sub>)<sub>2</sub>CFCN with OH radicals as a function of temperature (278-358 K): A good replacement for greenhouse SF<sub>6</sub>? Chem.Phys.Lett. <strong>2017</strong>, 687, 297-302.</p>

Kinetics of IO radicals with ethyl formate and ethyl acetate: A study using cavity ring-down spectroscopy and theoretical methods

The gas phase kinetics of the reactions of IO radicals with ethyl formate (EF) and ethyl acetate (EA) were investigated experimentally using cavity ring-down spectroscopy (CRDS). IO radicals were generated...