A novel photodegradation system implementing semi-continuous fluorescence excitation emission matrix (EEM) monitoring has been developed. This system allows for the rapid (~2 minutes) simultaneous collection of EEMs and absorbance spectra during solar-simulated irradiations in a flow-through system, providing an unprecedented amount of detail on the kinetic photochemical loss of dissolved natural organic matter (NOM) fluorescence. By collecting full EEMs every 20 minutes during 24 hour solar-simulated irradiations, photodegradation of Suwannee River natural organic matter (SRNOM) at various pHs was examined. Parallel factor analysis (PARAFAC) was used to isolate the photolabile and pH-influenced fluorescent components of SRNOM. Kinetic analysis showed significantly increasing rates of fluorescence loss with increasing pH. This has large implications for the photodegradation of NOM during estuarine mixing, when substantial increases of pH are common. The influence of pH on fluorescence and photodegradation kinetics emphasizes the need for pH to be monitored and controlled during photochemical laboratory experiments.  Further, the pH dependence of EEMs and photodegradation kinetics of NOM has the potential to be a useful analytical tool for the characterization of NOM from different sources.

pH effects on DOM photodegradation using semi-continuous fluorescence excitation emission matrices

249th National Meeting (2015)

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