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^(-10)and(2.07±0.14)×10^(-10)cm^(3)/(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.