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 C5aldehydes(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) × 10-10and(2.07 ± 0.14) × 10-10cm3/(molecule·sec) for 3-methyl-2-butenal and 3-methylbutanal, respectively. Additionally, the gas-phase products were also identified by PTR-MS, and the possible reaction mechanisms were proposed basing on the identified products. The detected gas-phase products are similar for two C5aldehydes reactions,mainly including small molecules of aldehydes, ketones and chlorinated aldehyde compounds. The atmospheric lifetimes(τ) calculated for 3-methyl-2-butenal(τ = 7.0 hr, marine boundary layer(MBL)) and 3-methylbutanal(τ = 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 C5aldehyde compounds.