title: Contribution of fulvic acid to the photochemical formation of Fe(II) in acidic Suwannee River fulvic acid solutions.
abstract: We investigated the contribution of fulvic acid to the photoformation of Fe(II) using aqueous Suwannee River fulvic acid (SRFA) as a surrogate for the humic-like substances (HULIS) found in atmospheric condensed phases. The effects of pH (3.2, 4.1, and 5.0) and wavelength (313, 334, 366, and 405nm) on Fe(II) photoformation were studied using monochromatic radiation at 20 degrees C. We calculated the wavelength-dependent Fe(II) photoformation efficiency values ("E-value"), defined here as a weighted sum of the product of the quantum yield and molar absorptivity of each Fe(II)-forming chemical species, and found that the E-values of acidic SRFA solutions were similar to those of Fe(OH)(2+). In addition, a comparison showed that the acidic SRFA solutions did not form Fe(II) fast enough to account for the observed Fe(II) formation efficiencies of the aqueous extracts of authentic aerosol samples. It was observed that 17-73% of Fe(III) had been reduced to Fe(II) in the dark in acidic SRFA solutions with added Fe(III) ranging from 0.5 to 10muM. The results of this study suggest that HULIS is unlikely to be the major reducing ligand in the process of photochemical formation of Fe(II) in acidic atmospheric drops. However, HULIS could reduce Fe(III) to Fe(II) in the dark, which in turn, could be important for night-time ()OH formation via the reaction between Fe(II) and H(2)O(2) (the Fenton reaction).
authors.affiliation: Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the Ryukyus, 1 Senbaru Nishihara-cho, Okinawa 903-0213, Japan.
authors.forename: Takemitsu
authors.initials: T
authors.lastname: Arakaki
authors.forename: Kiwamu
authors.initials: K
authors.lastname: Saito
authors.forename: Kouichirou
authors.initials: K
authors.lastname: Okada
authors.forename: Hitomi
authors.initials: H
authors.lastname: Nakajima
authors.forename: Yuya
authors.initials: Y
authors.lastname: Hitomi
mesh_terms: D001578:Benzopyrans / Q000737:chemistry*; D005296:Ferrous Compounds / Q000138:chemical synthesis*; D006812:Humic Substances; D055668:Photochemical Processes; D045483:Rivers; D012996:Solutions
chemical_list: D001578:Benzopyrans; D005296:Ferrous Compounds; D006812:Humic Substances; D012996:Solutions; C005023:fulvic acid