Abstract of PhD Thesis

Atmospheric Chemistry of Dimethylphenols & Nitrophenols

Perla Bardini (2006), University College Cork

The atmospheric degradation of a series of phenolic compounds has been investigated in atmospheric simulation chambers. Rate coefficients for the reaction of the six dimethylphenol isomers with nitrate radicals were determined at 295 ± 2 K and atmospheric pressure using the relative rate technique. The results indicate that gas-phase reaction with nitrate radicals is an important atmospheric degradation processes for the dimethylphenols.

A detailed product study of the reaction of nitrate radicals with 2,6-dimethylphenol was performed in order to provide information on the reaction mechanism. The major gas-phase products were identified as 2,6-dimethyl-4-nitrophenol and nitric acid, with small amounts of 2,6-dimethyl-1,4-benzoquinone also produced. No significant secondary organic aerosol formation was observed. Based on these results, a mechanism for the reaction of dimethylphenols with NO3 has been proposed involving H-atom abstraction from the –OH group as the dominant reaction pathway.

The atmospheric photolysis of 2-nitrophenol and four methyl-nitrophenol isomers was also investigated at the European Photoreactor (EUPHORE) in Valencia, Spain. Photolysis rate coefficients for atmospheric photolysis were determined and compared to calculated values. The results indicate that although the nitrophenol compounds show high absorption cross sections, the effective quantum yields for photolysis are less than 0.004. Nevertheless, the photolytic lifetimes for the nitrophenols are significantly shorter than those for reaction with OH and NO3 radicals, thus confirming that photolysis is the main atmospheric degradation pathway for these compounds. Possible mechanisms for the photolysis of the nitrophenols are proposed. A significant finding of this work was that photolysis of 2-nitrophenol and the methyl-2-nitrophenol isomers produces high yields (average of 70%) of secondary organic aerosol. This has implications for laboratory studies of aromatic oxidation and may also be relevant in the polluted atmosphere.