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

The carbonate radical (CO) is a strong oxidative radical that is generated via the reactions of HCO/CO with hydroxyl radical (HO) or triplet states of dissolved organic matter (DOM) in sunlit surface water. The bimolecular reaction rate constants of CO with various DOM isolates ( [Formula: see text] ) were calculated as 15-239 (mg of C/L) s 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 (R = 0.93) with [Formula: see text] , and an empirical equation was established. Our results also demonstrate that CO 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 CO during DOM photobleaching. These results allow us to estimate the reactivity of DOM with CO and to evaluate the role of CO in sunlit surface water. It will also allow a better assessment of the concentration and utilization of CO during the application of advanced oxidation processes.