Gas-phase Ozone Oxidation of Monoterpenes: Gaseous and Particulate Products

Abstract

Atmospheric oxidation of monoterpenes contributes to formation of tropospheric ozone and secondary organic aerosol, but their products are poorly characterized. In this work, we report a series of outdoor smog chamber experiments to investigate both gaseous and particulate products in the ozone oxidation of four monoterpenes: α-pinene, β-pinene, Δ^3-carene, and sabinene. More than ten oxygenated products are detected and identified in each monoterpene/O_3 reaction by coupling derivatization techniques and GC/MS detection. A denuder/filter pack sampling system is used to separate and simultaneously collect gas and aerosol samples. The identified products, consisting of compounds containing carbonyl, hydroxyl, and carboxyl functional groups, are estimated to account for about 34–50%, 57%, 29–67%, and 24% of the reacted carbon mass for β-pinene, sabinene, α-pinene, and Δ^3-carene, respectively. The identified individual products account for >83%, ∼100%, >90%, and 61% of the aerosol mass produced in the ozone reaction of β-pinene, sabinene, α-pinene, and Δ^3-carene. The uncertainty in the yield data is estimated to be ∼ ±50%. Many of the products partition between gas and aerosol phases, and their gas-aerosol partitioning coefficients are determined and reported here. Reaction schemes are suggested to account for the products observed.