Rate coefficients for the reactions of OH radical and ozone with a series of unsaturated esters

Abstract

Unsaturated esters are emitted into the atmosphere from biogenic and anthropogenic sources. Their atmospheric degradation through reactions with the main atmospheric oxidants (OH, O3, NO3, Cl) contributes to the formation of important secondary pollutants. Kinetic and mechanistic parameters for these reactions are highly required in order to estimate the atmospheric lifetimes and hence the impacts of these important classes of VOCs. In this study, the gas-phase rate coefficients of the reaction of OH radical and O3 with a series of unsaturated esters are reported. The esters investigated include methyl methacrylate (MMA), ethyl methacrylate (EMA), n-propyl methacrylate (nPMA), n-butyl methacrylate (nBMA), iso-propyl methacrylate (iPMA), iso-butyl methacrylate (iBMA) and fully deuterated methyl methacrylate (MMA-D8). The measurement combined the pulsed laser photolysis-laser induced fluorescence for the OH studies in the temperature range 257-376K and a 7300 L atmospheric simulation chamber for the O3 reactions at 291 ± 2K. This work provides the first temperaturedependence studies of OH reaction with EMA, nPMA, iPMA and iBMA and of O3 reaction with nPMA, iPMA and iBMA at room temperature. The obtained data are discussed in terms of the structure reactivity relationships and their atmospheric consequences by estimating the atmospheric lifetimes for the studied esters with respect to O3, OH radical and other oxidant in the troposphere.

Estimation of rate coefficients for the reactions of O<sub>3</sub> with unsaturated organic compounds for use in automated mechanism construction

“…The influence of substituent group size is clearly apparent in the data for vinyl aldehydes and ketones, vinyl ethers and alk-1-enoic acid alkyl esters, for example as discussed by Ren et al (2019) for the esters. Accordingly, the follow- ing expression is used to describe the 298 K data,…”

Gas-phase reactivity of acyclic α,β-unsaturated carbonyls towards ozone

“…The rate coefficients for methyl methacrylate and 4-methyl-3-penten-2-one are in excellent agreement with previous determinations. [8][9][10]12 The ozonolysis of 3-penten-2one has been subject of three previous studies. [11][12][13] While consistent with Greene and Atkinson 11 and Sato et al 12 the rate coefficient determined in this work is around 30% higher than the first determination reported in literature.…”

“…x r ¼ k carbonyl k alkene (5) However, in the literature different approaches for establishing analogue structures can be found by replacing the substituent of interest by either (a) a hydrogen atom 7,12,16 or (b) a methyl group 6 or by (c) elimination of the -C(O)-or -C(O)Omoiety. 5,10 In Fig. 2 these methods are explained using as examples methyl methacrylate and methyl crotonate.…”

“…6,7 The kinetics of the ozonolysis reactions of a moderate number of a,b-unsaturated carbonyls have been studied using both the absolute and relative rate method. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] However, the systematic analysis of their reactivity towards O 3 is at best at the beginning. 28 It is quite common to relate a target compound to the reactivity of its core structure in order to explain and/or predict its behaviour towards one of the atmospheric oxidants.…”

Estimation of rate coefficients for the reactions of O<sub>3</sub> with unsaturated organic compounds for use in automated mechanism construction

“…The influence of substituent group size is clearly apparent in the data for vinyl aldehydes and ketones, vinyl ethers and alk-1enoic acid alkyl esters, e.g. as discussed recently by Ren et al (2019) for the esters. Accordingly, the following expression is used to describe the 298 K data,…”