Study on the reaction of 3-methyl-2-butenal and 3-methylbutanal with Cl atoms: kinetics and reaction mechanism

The reaction of Cl atoms with two C-5 aldehydes (3-methyl-2-butenal and 3-methylbutanal) were investigated by proton-transfer-reaction mass spectrum (PTR-MS) using smog chamber at 298 +/- 1 K and 760 Torr. A relative rate method was used to determine the rate constants of the title reactions with m-xylene and trans-2-butene as reference compounds: (3.04 +/- 0.18) x 10(-10) and (2.07 +/- 0.14) x 10(-10) cm(3)/(molecule.sec) for 3-methyl-2-butenal and 3-methylbutanal, respectively. Additionally, the gas-phase products were also identi-fied by PTR-MS, and the possible reaction mechanisms were proposed basing on the identi-fied products. The detected gas-phase products are similar for two C-5 aldehydes reactions, mainly including small molecules of aldehydes, ketones and chlorinated aldehyde com-pounds. The atmospheric lifetimes (tau) calculated for 3-methyl-2-butenal (tau = 7.0 hr, marine boundary layer (MBL)) and 3-methylbutanal (tau = 10.3 hr, MBL) according to the obtained rate constants. The results indicate that Cl atoms at MBL are competitive with OH radicals for the degradation contribution of C-5 aldehyde compounds. (C) 2022 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.