Photochemical formation of carbonate radical and its reaction with dissolved organic matters

The carbonate radical (CO₃^•-) is a strong oxidative radical that is generated via the reactions of HCO₃^-/CO₃^2- with hydroxyl radical (HO^•) or triplet states of dissolved organic matter (³DOM^∗) in sunlit surface water. The bimolecular reaction rate constants of CO₃^•- with various DOM isolates ( [Formula: see text] ) were calculated as 15-239 (mg of C/L)^-1 s^-1 and were correlate to the bulk DOM properties, such as the content of phenolic moieties, the specific UV absorbance (SUVA), the E2/E3 value, and the fluorescence index (FI). The spectroscopic E2/E3 values was found to strongly correlated (R² = 0.93) with [Formula: see text] , and an empirical equation was established. Our results also demonstrate that CO₃^•- is involved in the photobleaching of dissolved organic matter (DOM) and in particular reacts with electron-donor moieties, leading to faster decay rates at long wavelengths of UV-vis absorption. Furthermore, a model was developed to calculate the steady-state concentrations of CO₃^•- during DOM photobleaching. These results allow us to estimate the reactivity of DOM with CO₃^•- and to evaluate the role of CO₃^•- in sunlit surface water. It will also allow a better assessment of the concentration and utilization of CO₃^•- during the application of advanced oxidation processes.