Phototransformation of 4-phenoxyphenol sensitised by 4-carboxybenzophenone: Evidence of new photochemical pathways in the bulk aqueous phase and on the surface of aerosol deliquescent particles

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• 作者：Elisa De Laurentiis ; Joanna Socorro ; Davide Vione ; Etienne Quivet ; Marcello Brigante ; Gilles Mailhot ; Henri Wortham ; Sasho Gligorovski
• 关键词：Atmospheric photosensitisers ; Triplet-sensitised photochemical reactions ; Humic-like substances ; Atmospheric aqueous phase ; Atmospheric aerosol ; Gas&ndash ; solid reactivity
• 刊名：Atmospheric Environment
• 出版年：December, 2013
• 年：2013
• 卷：81
• 期：Complete
• 页码：569-578
• 全文大小：1649 K

文摘

In addition to direct photolysis, degradation of organic compounds by solar light can also occur by indirect photolysis or photo-sensitised processes. These reactions are important because they are involved in, among others, direct and indirect climate changes, adverse health effects from inhaled particles, effects on cloud chemistry and ozone production. In this work, the importance of atmospheric photo-sensitisation is evaluated in bulk aqueous solution and on the surface of aerosol deliquescent particles. Irradiation experiments in aqueous solution indicate that 4-carboxybenzophenone (CBP) is able to photosensitise the degradation of 4-phenoxyphenol (4聽PP). The process takes place via the CBP triplet state (³CBP*), which has an oxidising nature. 4聽PP is fluorescent, unlike the photosensitiser CBP, with two emission bands at 鈭?20 and 鈭?80聽nm. However, addition of CBP to a 4聽PP solution considerably decreases the intensity of 4聽PP fluorescence bands and causes a very intense new band to appear at 鈭?20聽nm. This behaviour suggests a possible interaction between CBP and 4聽PP in solution, which could favour further light-induced processes. Moreover, the new band overlaps with the fluorescence spectrum of atmospheric HULIS (HUmic-LIke Substances), suggesting that supramolecular photosensitiser-substrate interactions may have a role in HULIS fluorescence properties. The interaction between CBP and 4聽PP coated on silica particles (gas-solid system) was also investigated under simulated sunlight, and in the presence of variable relative humidity. The water molecules inhibit the degradation of 4聽PP, induced by ³CBP* on the surface of aerosol particles, indicating that the process could be even faster on particles than in solution. We demonstrate that phenol substances adsorbed on aerosol surfaces and in bulk solution are substantially altered upon photosensitised processes.