title: Characterization of spectral responses of humic substances upon UV irradiation using two-dimensional correlation spectroscopy.
abstract: The spectral responses of a leaf litter derived humic substance (LLHS) and Suwannee River fulvic acid (SRFA) upon ultraviolet (UV) A irradiation were characterized using two-dimensional correlation spectroscopy (2D-COS) based on the absorption and the synchronous fluorescence spectra at different irradiation times. A 12 day irradiation on the humic substances (HS) resulted in higher reduction of the absorbance relative to the dissolved organic carbon concentration, suggesting that aromatic chromophores were preferentially oxidized and/or non UV-absorbing compounds were generated by the photobleaching. Synchronous fluorescence spectra revealed the preferential removal of fulvic-like and humic-like fluorophores and delayed response of protein-like fluorescence upon the irradiation. The spectral features at long wavelengths (>430 nm) appear to be affected by intra-molecular interactions of the individual chromophores associated with shorter wavelengths. Absorption-based 2D-COS demonstrated that there are three types of absorption bands for the two HS, which changed sequentially in the order of 290-400 nm → 200-250 nm → 250-290 nm. In addition, two or three distinctive fluorescence bands in response to the irradiation were identified from 2D-COS. The sequential orders and the associated wavelength bands were possibly explained by the irradiation wavelengths and the differences between direct and indirect photochemical reactions. The interpretation of the 2D-COS results was very consistent with the kinetic rate constants individually calculated at several discrete wavelengths. Our study demonstrated that 2D-COS could be used as a powerful tool in identifying distinctive bands of HS that have dissimilar behavior and the associated sequential orders by visualizing the spectral changes at continuous wavelengths.
authors.affiliation: Department of Environment and Energy, Sejong University, Seoul, South Korea. jinhur@sejong.ac.kr
authors.forename: Jin
authors.initials: J
authors.lastname: Hur
authors.forename: Ka-Young
authors.initials: KY
authors.lastname: Jung
authors.forename: Young Mee
authors.initials: YM
authors.lastname: Jung
mesh_terms: D001578:Benzopyrans / Q000737:chemistry* / Q000528:radiation effects; D006812:Humic Substances / Q000032:analysis / Q000528:radiation effects*; D007700:Kinetics; D055668:Photochemical Processes; D045483:Rivers / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D014466:Ultraviolet Rays; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000528:radiation effects; D018508:Water Purification / Q000379:methods
chemical_list: D001578:Benzopyrans; D006812:Humic Substances; D014874:Water Pollutants, Chemical; C005023:fulvic acid