Abstract:

Biogenic sources dominate the annual emissions of volatile organic compounds to the atmosphere. A significant fraction of these are monoterpenes, which react with OH radicals, NO3 radicals, or O3 to form products that include organic nitrates, which sequester NOx and thereby impact O3 formation, and also highly oxidized compounds that partition to particles as secondary organic aerosol (SOA). Here I describe the results of studies in which we reacted five monoterpenes: ∆-3-carene, β-pinene, α-pinene, limonene, and ocimene with NO3 radicals (a major nighttime oxidant) and with OH radicals (a major daytime oxidant) in the presence of NOx. Whereas all these monoterpenes have the same molecular formula, C10H16, they differ by having 1, 2, or 3 C=C double bonds and 0, 1, or 2 rings. Experiments were conducted in an environmental chamber under conditions in which RO2• + RO2• reactions were dominant, and gas- and particle-phase products were analyzed using mass spectrometry, gas and liquid chromatography, infrared spectroscopy, and derivatization-spectrophotometric methods. The results provide insight into the effects of molecular structure on gas-phase oxidation mechanisms as well as the role of particle-phase accretion reactions in SOA formation.

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