University College Cork

Thesis title: Atmospheric Simulation Chamber Studies of the Ozonolysis of Green Leaf Volatiles.

Supervisor: Dr. John Wenger

Abstract:

Green leaf volatiles (GLVs) are a family of oxygenated hydrocarbons produced from the biochemical conversion of linoleic and linolenic acid within plants. The compounds (Z)-3-hexenyl acetate, (Z)-3-hexenol and (Z)-3-hexenal form an important subset of GLVs that are emitted into the atmosphere in large quantities. In order to understand their impact on the atmosphere, information on their atmospheric degradation processes is required.

A series of laboratory studies has been performed on the gas-phase ozonolysis of (Z)-3-hexenyl acetate, (Z)-3-hexenol, (Z)-3-hexenal and the structurally related compound, (Z)-3-hexene. Rate coefficients for the reactions were measured at 295 ± 2 K and atmospheric pressure. The kinetic data allows conclusions to be made on the effect of various functional groups on the reactivity of the GLVs towards ozone. Yields for the primary carbonyl, propanal, and the OH radical were also measured and the contribution of each Criegee intermediate towards the overall OH radical yield was determined. The molecular composition of secondary organic aerosol (SOA) produced from the ozonolysis of the GLVs was investigated by off-line analysis of filter samples. Many low molecular weight products were identified using two dimensional gas chromatography time-of-flight mass spectrometry, while liquid chromatography mass spectrometry proved effective in characterization of short and longer chain oligomers.

The extent of oligomer formation showed a large dependence on the functional group within the GLV molecule; although dimer formation was observed for all of the compounds, higher order oligomers were only produced to a significant extent in the SOA from (Z)-3-hexenol. This is attributed to the high reactivity of its first generation oxidation product, 3-hydroxypropanal, which can hydrate and readily undergo further reactions in the particle phase. The yields of SOA produced from the ozonolysis of (Z)-3-hexenyl acetate and (Z)-3-hexenol were determined under a variety of reaction conditions. The results indicate that the SOA yield increases for higher starting concentrations of GLV, lower relative humidity and in the presence of seed aerosol. SOA formation yields from (Z)-3-hexenol are higher than those from (Z)-3-hexenyl acetate. The results suggest that GLVs are a potentially important global source of SOA.

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• Undergraduate Physical Chemistry Practicals for 2nd Years (CM2003, CM2004, CM2007).
• Undergraduate Physical Chemistry Practicals for 3rd Years (CM3016, CM3017).
• Online Assessment (Moodle) for Physical Chemistry modules (CM2003, CM2004).
• Coordinator of 3rd Year Physical Chemistry Small Group Tutorials (CM3016, CM3017).
• Coordinator of Environmental Chemistry section for EV2001.
• Chemistry Educational Support Worker for UCC’s Disability Support Service.