Theoretical study on the atmospheric degradation mechanism and subsequent products of E,E-2,4-hexadienal with hydroxyl radical

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 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 us a better understanding for the main degradation products. The reaction paths of E,E-2,4-hexadienal with OH radical have been calculated accurately by using 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 exothermic reaction, the ten paths would contribute to the total reaction. Furthermore, the peroxy (RO2) and alkoxy (RO) radicals from the most important adduct IM1(CH3CHOHCHCH(sic)CHCHO) would be formed in the atmospheric environment. Hence, the reaction mechanism of the peroxy radical (CH3CHOHCHO2CH(sic)CHCHO) with NO, NO2, HO2, and self-reaction have been also studied by using the same quantum chemical methods. And the reaction paths of alkoxy radical (CH3CHOHCHOCH(sic)CHCHO) have been also originally studied. It is found that the subsequent reactions play a key role in the cycling of atmospheric radicals, production of ozone, and SOA formation. What is more, the reaction mechanism of this study accords with the reported experimental observations. Meanwhile, the theoretical rate constant of 1.05 x 10(-10) cm(3) molecule(-1) s(-1) of E,E-2,4-hexadienal with OH reaction at 298 K is close to experimental data. The atmospheric lifetime of E,E-2,4-hexadienal with OH radical is about 2.6 h at 298 K. This study provides insight into the transformation of E,E-2,4-hexadienal in the atmospheric environment.

Automated summary

E,E-2,4-hexadienal is likely a precursor of secondary organic aerosol (SOA) and is important in atmospheric chemistry. Quantum chemical calculations were used to study its reaction mechanism with hydroxyl radical, revealing multiple pathways and products that impact atmospheric radical cycling, ozone production, and SOA formation. The theoretical rate constant of the reaction at 298 K matches experimental data, with an atmospheric lifetime of about 2.6 h.