Theoretical study on the atmospheric degradation mechanism and
subsequent products of E,E-2,4-hexadienal with hydroxyl radical
Abstract
E,E-2,4-hexadienal is probably a precursor of secondary organic aerosol
(SOA) and plays an important role in the atmospheric chemistry. Its main
degradation routs are the reactions with OH, Cl, NO3 as well as
photolysis. Atmospheric hydroxyl radical, as the most important oxidant,
generally controls the removal of volatile organic compounds (VOCs) in
the atmosphere. Thus, the quantum chemical calculations are used to
investigate the reaction mechanism of E,E-2,4-hexadienal with hydroxyl
radical, which would give better understanding for the main degradation
products. The reaction paths of E,E-2,4-hexadienal with OH radical have
been calculated accurately at the BMC-CCSD//M06-2X/6-311G (d, p) level
at atmospheric pressure and room temperature. There are six hydrogen
abstraction and four carbon addition paths at the first stages of this
reaction. Due to the low energy barrier and reaction exotherm, the ten
paths would contribute to the total reaction. Furthermore, the peroxy
(RO2) and alkoxy (RO) radicals from the most important adduct
IM1(CH3CHOHCHCH=CHCHO) would be formed in the atmospheric environment.
The reaction mechanism of the peroxy radical (CH3CHOHCHO2CH=CHCHO) with
NO, NO2, HO2, and self-reaction have been studied by using the same
quantum chemical methods. And the reaction paths of alkoxy radical
(CH3CHOHCHOCH=CHCHO) have been also originally studied. The subsequent
reactions play a key role in the cycling of atmospheric radicals,
production of ozone, and SOA formation. What’s more, the reaction
mechanism of this study accords with the reported experimental
observations.