Dissolved Organic Matter Singlet Oxygen Quantum Yields: Evaluation Using Time-Resolved Singlet Oxygen Phosphorescence.

Singlet oxygen (O) generation quantum yields from chromophoric dissolved organic matter (CDOM) have been reported for many samples over the past 4 decades. Yet even for standardized isolates such as those from the International Humic Substance Society (IHSS), wide-ranging values exist in the literature. In this manuscript, time-resolved O phosphorescence was used to determine the O quantum yields (Φ) of a variety of dissolved organic matter (DOM) isolates and natural waters. In general, the O quantum yield values in this study are in the middle, although below the median of the range of past reported values (e.g., for Suwannee River Natural Organic Matter IHSS isolate: 1.8% vs 0.23-2.89%). Notably, hydrophobic neutral fractions of DOM isolates were found to possess the highest O quantum yields, an interesting result given that these fractions are not retained in typical humic and fulvic acid isolation procedures that use XAD resins. The excitation wavelength dependence of O generation from CDOM was also examined, and an approximate linear decrease with longer excitation wavelength was observed. This work advances the understanding of CDOM photoprocesses, especially in relation to wavelength-dependent O production, which is valuable for assessing real-world environmental behavior.