Atmospheric reactions between E,E-2,4-hexadienal and OH, NO3 radicals and Cl atoms

•Rate coefficients of E,E-2,4-hexadienal with OH, NO3 and Cl have been obtained.•Results suggest a double bond addition as the main reaction channel.•The estimated tropospheric lifetimes of E,E-2,4-hexadienal are very short.•The reaction with NO3 and its photodegradation could be the main sinks.

E,E-2,4-Hexadienal is an α,β-unsaturated aldehyde whose presence in the atmosphere can arise from different sources. The rate coefficients for the reaction of this compound with Cl atoms, OH and NO3 radicals and for the photolysis process have been determined at atmospheric pressure and room temperature. A relative method has been developed with a Fourier Transform Infrared spectrometer (FTIR) or Solid Phase Micro Extraction fiber/chromatography-mass spectrometer (SPME/GC-MS) used as sampling/detection techniques. The absolute rate coefficients k (in units of cm3 molecule−1 s−1) obtained for Cl, OH and NO3 were (3.98 ± 0.44) × 10−10, (6.78 ± 0.47) × 10−11 and (1.34 ± 0.56) × 10−12, respectively. An estimation of the rate coefficient for the reaction of E,E-2,4-hexadienal with OH and NO3 radicals and Cl atoms has been carried out using correlations and SAR methods. The SAR substituent factor for the -C(O)H group, [G-(C(O)H)] = 3.58 × 10−3, has been obtained. This group reactivity factor allows the rate coefficients to be estimated for the reaction of unsaturated aldehydes with NO3 radicals. The results of this study confirm that the reaction of unsaturated aldehydes with Cl atoms is very fast and that the structure of the compound has little influence, with the influence of the structure being more marked in the case of the OH radical reaction and relatively large for the NO3 reaction. The results are consistent with a mechanism in which the first stage is addition of an atom or radical to the double bond of E,E-2,4-hexadienal as the main reaction channel and, to a minor extent, the abstraction of aldehydic hydrogen. These are the first data reported for the atmospheric reactions of this compound and this study therefore contributes to the database of rate coefficients for atmospheric reactions.

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