Atmospheric fate of a series of saturated alcohols: Kinetic and mechanistic study

Abstract

The atmospheric fate of a series of saturated alcohols (SAs) was evaluated through kinetic and reaction product studies with the main atmospheric oxidants. These SAs are alcohols that could be used as fuel additives. Rate coefficients (in cm3 molecule-1 s-1) measured at ∼ 298K and atmospheric pressure (720±20 Torr) were as follows: k1 ((E)-4-methylcyclohexanol C Cl) D (3:70±0:16) ×10-10, k2 ((E)-4-methylcyclohexanol C OH) D (1:87±0:14) ×10-11, k3 ((E)-4-methylcyclohexanol C NO3) D (2:69±0:37) ×10-15, k4 (3,3-dimethyl-1-butanol C Cl) D (2:69±0:16) ×10-10, k5 (3,3-dimethyl-1-butanol C OH) D (5:33±0:16) ×10-12, k6 (3,3-dimethyl-2-butanol C Cl) D (1:21±0:07) ×10-10, and k7 (3,3-dimethyl-2-butanol C OH) D (10:50±0:25) ×10-12. The main products detected in the reaction of SAs with Cl atoms (in the absence/presence of NOx), OH radicals, and NO3 radicals were (E)-4-methylcyclohexanone for the reactions of (E)-4-methylcyclohexanol, 3,3-dimethylbutanal for the reactions of 3,3-dimethyl-1-butanol, and 3,3-dimethyl-2-butanone for the reactions of 3,3-dimethyl-2-butanol. Other products such as formaldehyde, 2,2-dimethylpropanal, and acetone have also been identified in the reactions of Cl atoms and OH radicals with 3,3-dimethyl-1-butanol and 3,3-dimethyl-2-butanol. In addition, the molar yields of the reaction products were estimated. The products detected indicate a hydrogen atom abstraction mechanism at different sites on the carbon chain of alcohol in the case of Cl reactions and a predominant site in the case of OH and NO3 reactions, confirming the predictions of structure-activity relationship (SAR) methods. Tropospheric lifetimes (τ) of these SAs have been calculated using the experimental rate coefficients. Lifetimes are in the range of 0.6-2 d for OH reactions, 7-13 d for NO3 radical reactions, and 1-3 months for Cl atoms. In coastal areas, the lifetime due to the reaction with Cl decreases to hours. The calculated global tropospheric lifetimes, and the polyfunctional compounds detected as reaction products in this work, imply that SAs could contribute to the formation of ozone and nitrated compounds at local, regional, and even global scales. Therefore, the use of saturated alcohols as additives in diesel blends should be considered with caution.