Study of the tropospheric degradation of 2-methylbutanal initiated by OH radicals, Cl atoms and sunlight
Authors: Asensio María , Blázquez Sergio , Antiñolo María , Albadalejo José , Jiménez Elena 
Published: March 2021

&lt;p&gt;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&lt;sup&gt;1&lt;/sup&gt;. Moreover, some industrial operations also generate 2MB&lt;sup&gt;2&lt;/sup&gt;. 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&lt;sup&gt;3&lt;/sup&gt;. The photolysis rate coefficients (&lt;em&gt;J&lt;/em&gt;) of 2MB initiated by sunlight have also been reported&lt;sup&gt;4&lt;/sup&gt;. However, there is no available data for the reaction of Cl atoms with 2MB and the photolysis products.&lt;/p&gt;&lt;p&gt;In this work, the photolysis rate coefficient (&lt;em&gt;J&lt;/em&gt;) 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 (&lt;em&gt;k&lt;/em&gt;&lt;sub&gt;Cl&lt;/sub&gt;) and OH (&lt;em&gt;k&lt;/em&gt;&lt;sub&gt;OH&lt;/sub&gt;) 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&lt;sub&gt;x&lt;/sub&gt; 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 &lt;sup&gt;5&lt;/sup&gt; of air, whereas for the absolute kinetics of the OH-reaction, &lt;em&gt;k&lt;/em&gt;&lt;sub&gt;OH&lt;/sub&gt; 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&lt;sup&gt;6&lt;/sup&gt;. 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.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;REFERENCES:&lt;/strong&gt; &lt;strong&gt;1&lt;/strong&gt;. 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. &lt;strong&gt;2018&lt;/strong&gt;, 162, 499&amp;#8211;508. &lt;strong&gt;2. &lt;/strong&gt;Kolar, P.; Kastner, J. R. Low-Temperature Catalytic Oxidation of Aldehyde Mixtures Using Wood Fly Ash: Kinetics, Mechanism, and Effect of Ozone. Chemosphere. &lt;strong&gt;2010&lt;/strong&gt;, 78 (9), 1110&amp;#8211;1115. &lt;strong&gt;3. &lt;/strong&gt;D&amp;#8217;Anna, B.; Andresen, O.; Gefen, Z. and Nielsen, C.J.: Kinetic study of OH and NO&lt;sub&gt;3&lt;/sub&gt; radical reactions with 14 aliphatic aldehydes. Phys.Chem.Chem.Phys. &lt;strong&gt;2001&lt;/strong&gt;, 3, 3057-3063. &lt;strong&gt;4. &lt;/strong&gt;Wenger, J.C.: Chamber Studies on the Photolysis of Aldehydes. Environmental Simulation Chambers: Application to Atmospheric Chemical Processes. &lt;strong&gt;2006. &lt;/strong&gt;Nato Science Series: IV: Earth and Environmental Science, vol 62. Springer, Dordrecht. &lt;strong&gt;5. &lt;/strong&gt;Anti&amp;#241;olo, M.; Asensio, M.; Albadalejo, J. and Jim&amp;#233;nez E.: Gas-Phase Reaction of trans-2-methyl-2-butenal with Cl: Kinetics, Gaseous Products, and SOA Formation. Atmosphere &lt;strong&gt;2020&lt;/strong&gt;, 11 (7), 715. &lt;strong&gt;6. &lt;/strong&gt;Bl&amp;#225;zquez, S.; Anti&amp;#241;olo, M.; Nielsen, O. J.; Albadalejo, J. and Jim&amp;#233;nez, E.: Reaction kinetics of (CF&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;CFCN with OH radicals as a function of temperature (278-358 K): A good replacement for greenhouse SF&lt;sub&gt;6&lt;/sub&gt;? Chem.Phys.Lett. &lt;strong&gt;2017&lt;/strong&gt;, 687, 297-302.&lt;/p&gt;