title: Investigation of the Coupled Effects of Molecular Weight and Charge-Transfer Interactions on the Optical and Photochemical Properties of Dissolved Organic Matter.
abstract: We studied the formation of photochemically produced reactive intermediates (RI) from dissolved organic matter (DOM). Specifically, we focused on the effects of variable molecular weight and chemical reduction on the optical properties of DOM (absorbance and fluorescence) and the formation of singlet oxygen ((1)O2), DOM triplet excited states ((3)DOM*), and the hydroxyl radical ((•)OH). The data are largely evaluated in terms of a charge-transfer (CT) model, but deficiencies in the model to explain the data are pointed out when evident. A total of two sets of samples were studied that were subjected to different treatments; the first set included secondary-treated wastewaters and a wastewater-impacted stream, and the second was a DOM isolate. Treatments included size fractionation and chemical reduction using sodium borohydride. Taken as a whole, the results demonstrate that decreasing molecular weight and borohydride reduction work in opposition regarding quantum efficiencies for (1)O2 and (3)DOM* production but in concert for fluorescence and (•)OH production. The optical and photochemical data provide evidence for a limited role of CT interactions occurring in lower-molecular-weight DOM molecules. In addition, the data suggest that the observed optical and photochemical properties of DOM are a result of multiple populations of chromophores and that their relative contribution is changed by molecular-weight fractionation and borohydride reduction.
authors.affiliation: Department of Civil, Environmental, and Architectural Engineering, University of Colorado , Boulder, Colorado 80309, United States.
authors.forename: Garrett
authors.initials: G
authors.lastname: McKay
authors.affiliation: Department of Civil, Environmental, and Architectural Engineering, University of Colorado , Boulder, Colorado 80309, United States.|Department of Chemistry and Biochemistry, California State University , Long Beach, California 90840, United States.
authors.forename: Kylie D
authors.initials: KD
authors.lastname: Couch
authors.affiliation: Department of Chemistry and Biochemistry, California State University , Long Beach, California 90840, United States.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Mezyk
authors.affiliation: Department of Civil, Environmental, and Architectural Engineering, University of Colorado , Boulder, Colorado 80309, United States.
authors.forename: Fernando L
authors.initials: FL
authors.lastname: Rosario-Ortiz
mesh_terms: D017665:Hydroxyl Radical / Q000737:chemistry; D008962:Models, Theoretical; D008970:Molecular Weight; D009930:Organic Chemicals / Q000737:chemistry; D026082:Singlet Oxygen / Q000737:chemistry; D062065:Wastewater
chemical_list: D017665:Hydroxyl Radical; D009930:Organic Chemicals; D026082:Singlet Oxygen; D062065:Wastewater