Heterogeneous reactions of NO₃ and N₂O₅ with organic substrates of atmospheric relevance

Atmospheric heterogeneous reaction could modify the physical properties and chemical composition of aerosol particles, thereby affecting their roles in climate, air pollution, and human health. The current knowledge of heterogeneous reactions between nighttime gas-phase oxidants and organic aerosols is very limited. The goal of this thesis was to contribute to the understanding of such reactions, particularly to the kinetics of NO₃ and N₂O₅ reactions with a variety of organic substrates and mixtures that can serve as proxies for aerosol particles. In the first series of studies, we investigated the reactive uptake of NO₃ with binary organic mixtures of an unsaturated organic (methyl oleate) and saturated molecules as “matrix molecules”. For liquid mixtures, the uptake coefficients (γ) of the matrices were significantly increased with the addition of small amounts of methyl oleate. The increase can vary by a factor of 5 depending on the type of matrix used. For solid-liquid mixtures, the uptake coefficient decreased by a factor of 10 after exposure to NO₃ for 90 minutes. For all liquid mixtures, the atmospheric lifetime was estimated on the order of a few minutes (with an upper limit of 35 mins), whereas, for liquid-solid mixtures, a lower limit to the lifetime was estimated to be 1-2 hours. In the second series of studies, we investigated NO₃ uptake on solid tridecanal and the uptake on liquid binary mixtures containing tridecanal and saturated organics as matrices. Uptake on the solid tridecanal was shown to be efficient, with γ = (1.6 ± 0.8) ×10–². For liquid binary mixtures, the uptake coefficient also depended on the matrix molecule. The atmospheric lifetime of aldehydes was estimated to range from 1.9–7.5 h due to NO₃ oxidation. In the third series of studies, we investigated the N₂O₅ uptake kinetics on alcohols. The uptake coefficients of N₂O₅ for five different alcohols at 293 K varied by 2 orders of magnitude, ranging from 3×10–⁴ to 1.8×10–². The atmospheric lifetime of alcohols was calculated to range from 0.6–130 h, depending on the physical and chemical properties of the organic liquid.Science, Faculty ofChemistry, Department ofGraduat