Atmospheric oxidation of long chain aldehydes: OH and Cl reactivity, mechanisms and environmental impact

Abstract

The relative-rate technique has been used to obtain the rate coefficients for the reactions of the saturated aldehydes (SA): Octanal (OCT) CH3(CH2)6C(O)H and Nonanal (NON) CH3(CH2)7C(O)H with OH radicals and Cl atoms at (298 ± 3) K and atmospheric pressure. The experiments were performed in an environmental chamber using in situ FTIR spectroscopy detection to monitor the decay of the aldehydes relative to different reference compounds. The following room temperature rate coefficients (in units of cm3 molecule− 1 s − 1 ) were obtained: k1 (OH + CH3(CH2)6C(O)H) = (3.13 ± 0.50) × 10− 11, k2 (Cl + CH3(CH2)6C(O)H) = (2.80 ± 0.31) £10− 10, k3 (OH + CH3(CH2)7C(O)H) = (2.81 ± 0.40) × 10− 11 and k4 (Cl + CH3(CH2)7C(O)H) = (3.10 ± 0.30) × 10− 10. In addition, product studies were performed in similar conditions of the kinetic experiments by the SPME-GC-MS technique. Heptanal, hepta-1-ol, octanoic acid, octanal, 1-octanol, octanoyl chloride, 1-chlorooctane and formaldehyde were identified as reaction products. The atmospheric implications of the studied reactions were assessed by the estimation of the tropospheric lifetimes of OCT and NON concerning their reaction with OH radicals and Cl atoms to be 9, 10 h and 30, 27 h, respectively. The relatively short residence in the atmosphere of the SA studied will have a local impact with restricted transport. High tropospheric ozone creation potential of 68 and 66 were estimated for OCT and NON, respectively.