Research following the Deepwater Horizon disaster suggests that photochemical oxygenation (PO) of oil produces partially oxidized, polar material that is persistent and recalcitrant to further degradation.1 The nature of the underlying reactions is unknown, particularly with regard to the identity of the primary oxidant, although there is reason to suspect the involvement of excited oxygen species, such as hydroxyl radical (●OH) and singlet oxygen (1O2).2-4 To better assess the role that 1O2 might play in oil PO we conducted studies to measure the apparent quantum yields (AQY) for 1O2 formation and PO at several UV and VIS wavelengths for oil samples from active fields and slicks collected from spills and seeps. AQYs for 1O2 were determined relative to quantum yield standards using time-resolved phosphorescence detection of 1O2 in oil dissolved in air equilibrated CH2Cl2. Bimolecular rate constants for 1O2 quenching (kq) were also determined for some oils. AQYs of PO were determined for oil films on water by following the photochemical loss of dissolved O2(aq). Solar spectral weighted 1O2 AQYs ranged from 0.11 to 0.29, and tended to be higher for lighter colored and less weathered oils. In contrast, 1O2 quenching rate constants tended to be higher for heavier, more weathered oils. Correlations were observed between oil optical properties and 1O2 AQYs and kq: in particular, the spectral slope parameter (S300-600) correlated directly with AQYs and inversely with kq. Surprisingly, PO AQYs displayed no clear relationship to oil properties, although the highest AQYs were observed in samples with high 1O2 AQYs.

Apparent quantum yields of singlet oxygen and photochemical oxygen consumption for crude oils

255th National Meeting (2018)

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