Reassessing the Quantum Yield and Reactivity of Triplet-State Dissolved Organic Matter via Global Kinetic Modeling

Measuring the quantum yield and reactivity of triplet-state dissolved organic matter ((DOM)-D-3*) is essential for assessing the impact of DOM on aquatic photochemical processes. However, current (DOM)-D-3* quantification methods require multiple fitting steps and rely on steady-state approximations under stringent application criteria, which may introduce certain inaccuracies in the estimation of DOM photoreactivity parameters. Here, we developed a global kinetic model to simulate the reaction kinetics of the hv/DOM system using four DOM types and 2,4,6-trimethylphenol as the probe for (DOM)-D-3*. Analyses of residuals and the root-mean-square error validated the exceptional precision of the new model compared to conventional methods. (DOM)-D-3* in the global kinetic model consistently displayed a lower quantum yield and higher reactivity than those in local regression models, indicating that the generation and reactivity of (DOM)-D-3* have often been overestimated and underestimated, respectively. The global kinetic model derives parameters by simultaneously fitting probe degradation kinetics under different conditions and considers the temporally increasing concentrations of the involved reactive species. It minimizes error propagation and offers insights into the interactions of different species, thereby providing advantages in accuracy, robustness, and interpretability. This study significantly advances the understanding of (DOM)-D-3* behavior and provides a valuable kinetic model for aquatic photochemistry research.