title: Photogeneration of reactive transient species upon irradiation of natural water samples: Formation quantum yields in different spectral intervals, and implications for the photochemistry of surface waters.
abstract: Chromophoric dissolved organic matter (CDOM) in surface waters is a photochemical source of several transient species such as CDOM triplet states ((3)CDOM*), singlet oxygen ((1)O2) and the hydroxyl radical (OH). By irradiation of lake water samples, it is shown here that the quantum yields for the formation of these transients by CDOM vary depending on the irradiation wavelength range, in the order UVB > UVA > blue. A possible explanation is that radiation at longer wavelengths is preferentially absorbed by the larger CDOM fractions, which show lesser photoactivity compared to smaller CDOM moieties. The quantum yield variations in different spectral ranges were definitely more marked for (3)CDOM* and OH compared to (1)O2. The decrease of the quantum yields with increasing wavelength has important implications for the photochemistry of surface waters, because long-wavelength radiation penetrates deeper in water columns compared to short-wavelength radiation. The average steady-state concentrations of the transients ((3)CDOM*, (1)O2 and OH) were modelled in water columns of different depths, based on the experimentally determined wavelength trends of the formation quantum yields. Important differences were found between such modelling results and those obtained in a wavelength-independent quantum yield scenario.
authors: Università di Torino, Dipartimento di Chimica, Via Pietro Giuria 5, 10125 Torino, Italy.
authors: Andrea
authors: A
authors: Marchisio
authors: Università di Torino, Dipartimento di Chimica, Via Pietro Giuria 5, 10125 Torino, Italy.
authors: Marco
authors: M
authors: Minella
authors: Università di Torino, Dipartimento di Chimica, Via Pietro Giuria 5, 10125 Torino, Italy.
authors: Valter
authors: V
authors: Maurino
authors: Università di Torino, Dipartimento di Chimica, Via Pietro Giuria 5, 10125 Torino, Italy.
authors: Claudio
authors: C
authors: Minero
authors: Università di Torino, Dipartimento di Chimica, Via Pietro Giuria 5, 10125 Torino, Italy; Università di Torino, Centro Interdipartimentale NatRisk, Via L. Da Vinci 44, 10095 Grugliasco, TO, Italy. Electronic address: davide.vione@unito.it.
authors: Davide
authors: D
authors: Vione
mesh_terms: D006812:Humic Substances / Q000528:radiation effects*; D017665:Hydroxyl Radical / Q000528:radiation effects*; D060106:Lakes / Q000737:chemistry*; D008962:Models, Theoretical; D010100:Oxygen / Q000528:radiation effects*; D055668:Photochemical Processes
chemical_list: D006812:Humic Substances; D017665:Hydroxyl Radical; D010100:Oxygen
keywords: Environmental photochemistry; Indirect photochemistry; Photogeneration quantum yields; Sensitised photolysis; Spectral intervals