Characterizing the transformation of aquatic humic substances exposed to ultraviolet radiation using excitation–emission matrix fluorescence spectroscopy and PARAFAC

ABSTRACTIt is important to understand the change in aquatic humic substances (AHS) induced by light due to the upward trend in ultraviolet (UV) radiation reaching the surface of the Earth. Changes in the quantity and quality of AHS in AHS-rich wetland water exposed to UV-A or UV-B light were determined using 3-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy combined with parallel factor analysis (PARAFAC) and a resin isolation method. The dissolved organic carbon and AHS-carbon concentrations decreased via photodegradation with UV-A or UV-B exposure. The decreases in both carbon concentrations were greater when exposed to UV-B than when exposed to UV-A. Three AHS-like components were detected by EEM-PARAFAC: AHS-1, AHS-2, and AHS-3. AHS-1 and AHS-3 were degraded more by UV-A and UV-B exposure, respectively. AHS-2 was degraded slightly by UV-A exposure, whereas exposure to UV-B generated AHS-2 in the presence of low-molecular-weight compounds, and then underwent photodegradation. AHS...