Mechanism of atmospheric ozonolysis of sabinene: A DFT study

Terpenes, which are important constituents of biogenic nonmethane organic compounds (NMOCs) in the atmosphere, play an important role in the tropospheric chemistry because of their large emission rates and their strong reactivity. The most important terpenes are α-pinene, β-pinene, sabinene and d-limonene, accounting for 40-80% of the overall terpene emissions on a global scale. The atmospheric chemistry of terpenes has not been fully understood due to the short-lifetime of their oxidized radical intermediates, and the extreme difficulty in the detection of these species experimentally. In this paper, we carried out molecular orbital theory calculations for the atmospheric ozonolysis of sabinene. The profile of the potential energy surface was constructed. The calculated results were compared with the available experimental observations. Several experimentally uncertain compounds were determined. The theoretical study shows that the dominant products of the atmospheric ozonolysis of sabinene are sabinaketone, formaldehyde and formic acid. Sabinaketone is a low vapor pressure compounds and is inclined to form secondary organic aerosols (SOAs). An energetically favorable formation pathway for 3-oxo-sabina ketone is revealed for the first time.