Photo-Induced OH reactions of naphthalene and its oxidation products on SiO2

The photo-induced degradation of naphthalene, 1,4-naphthoquinone, 1-naphthol and 1-NO₂ naphthalene, adsorbed on silica gel, and with the addition of nitrogenous air pollutants e.g. NO₂ (as KNO₂) was investigated. Results indicate that compounds adsorbed onto a solid carrier are degraded when irradiated with UV light (λ > 290 nm) in the presence of nitrites. The key species initiating the naphthalene degradation is the OH-radical which is generated through the photolysis of NO₂. Reaction products identified were 2-formyl-cinnamaldehyde, 1,4-naphthoquinone, nitronaphthol, o-phthaldialdehyde, phthalide and nitronaphthalene. A mass balance between 40–50% was achieved. Under the same irradiation conditions, 1-NO₂ naphthalene is mainly degraded by direct photolysis while degradation of 1-naphthol and 1,4-naphthoquinone proceeds via the reaction with OH-radicals. Identified products were hydroxy-nitro-nitroso- and quinones compounds.