Abstract
Abstract. The kinetics of the gas phase reactions of hydroxyl radicals with two unsaturated ketoethers (UKEs) at (298±3) K and 1 atm of synthetic air have been studied for the first time using the relative-rate technique in an environmental reaction chamber by in situ Fourier-transform infrared spectroscopy (FTIR). The rate coefficients obtained using propene and isobutene as reference compounds were (in units of 10−10 cm3 molecule−1 s−1) as follows: kTMBO (OH + (E)-4-methoxy-3-buten-2-one) = (1.41±0.11) and kMMPO (OH + (1E)-1-methoxy-2-methyl-1-penten-3-one) = (3.34±0.43). In addition, quantification of the main oxidation products in the presence of NOx has been performed, and degradation mechanisms for these reactions were developed. Methyl formate, methyl glyoxal, peroxyacetyl nitrate (PAN) and peroxypropionyl nitrate (PPN) were identified as main reaction products and quantified for both reactions. The results of the present study provide new insights regarding the contribution of these multifunctional volatile organic compounds (VOCs) in the generation of secondary organic aerosols (SOAs) and long-lived nitrogen containing compounds in the atmosphere. Atmospheric lifetimes and implications are discussed in light of the obtained results.
Highlights
Oxygenated volatile organic compounds (OVOCs) are ubiquitous atmospheric constituents of anthropogenic and natural origin
4 Results and discussion 4.1 Rate coefficients for the reaction with OH radicals Plots of the kinetic data obtained from the experiments of the reaction of OH radicals with TMBO and MMPO using two different reference compounds are shown in Figs. 1 and 2, respectively
Once emitted into the atmosphere, it is expected that unsaturated ketoethers such as TMBO and MMPO will follow gas phase degradation processes initiated by the main tropospheric oxidants (OH radicals, ozone, chlorine atoms and NO3 radicals)
Summary
Oxygenated volatile organic compounds (OVOCs) are ubiquitous atmospheric constituents of anthropogenic and natural origin. Ketones are one of the dominant groups of carbonyls found in the lower troposphere They can be emitted into the atmosphere by anthropogenic activities from industry and combustion engine vehicle exhaust and in a large extent are formed as reaction products of other volatile organic compounds (VOCs) in the troposphere (Calvert et al, 2011; Jiménez et al, 2014; Mellouki et al, 2015). Namely the α, βunsaturated ketones and α, β-unsaturated ethers are either emitted by plants or are produced as a result of atmospheric oxidation of conjugated dienes (Lv et al, 2018; Mellouki et al, 2015; Zhou et al, 2006) These compounds have been considered as precursors for secondary organic aerosols (SOAs) (Calvert et al, 2011). The obtained results could be used to generate more complete atmospheric chemical degradation mechanisms, i.e. the master chemical mechanism, which is necessary for a better estimation of the contribution of such compounds to photooxidant and SOAs formation
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