Abstract
The gas-phase reaction between trans-2-methyl-2-butenal and chlorine (Cl) atoms has been studied in a simulation chamber at 298 ± 2 K and 760 ± 5 Torr of air under free-NOx conditions. The rate coefficient of this reaction was determined as k = (2.45 ± 0.32) × 10-10 cm3 molecule−1 s−1 by using a relative method and Fourier transform infrared spectroscopy. In addition to this technique, gas chromatography coupled to mass spectrometry and proton transfer time-of-flight mass spectrometry were used to detect and monitor the time evolution of the gas-phase reaction products. The major primary reaction product from the addition of Cl to the C-3 of trans-2-methyl-2-butenal was 3-chloro-2-butanone, with a molar yield (YProd) of (52.5 ± 7.3)%. Acetaldehyde (Y = (40.8 ± 0.6)%) and HCl were also identified, indicating that the H-abstraction by Cl from the aldehyde group is a reaction pathway as well. Secondary organic aerosol (SOA) formation was investigated by using a fast mobility particle sizer spectrometer. The SOA yield in the Cl + trans-2-methyl-2-butenal reaction is reported to be lower than 2.4%, thus its impact can be considered negligible. The atmospheric importance of the titled reaction is similar to the corresponding OH reaction in areas with high Cl concentration.
Highlights
Carbonyl compounds are volatile organic compounds (VOCs) emitted into the troposphere by several natural sources and by on-road traffic [1,2,3]
The gas-phase kinetics of trans-2-methyl-2-butenal was experimentally studied with OH radicals and O3 [13,14] and an estimation was reported for the NO3
This section includes the experimental results for the kinetic and product studies for reaction (R1), presenting the measurement of the Cl-rate coefficient, the identification of products both in the gas and particle phases, and the determination of the Secondary organic aerosol (SOA) yield
Summary
Carbonyl compounds are volatile organic compounds (VOCs) emitted into the troposphere by several natural sources and by on-road traffic [1,2,3]. They can be generated through the oxidation of other VOCs present in the troposphere [4]. Unsaturated carbonyls, such as trans-2-methyl-2-butenal (E-CH3 CH=C(CH3 )C(O)H), are emitted into the lower atmosphere from vegetation and human activities such as road vehicles and industries, and methylbutenals have been proposed as oxidation products of isoprene initiated by hydroxyl (OH) radicals in the presence of NO [5,6]. The gas-phase kinetics of trans-2-methyl-2-butenal was experimentally studied with OH radicals and O3 [13,14] and an estimation was reported for the NO3
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