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

Abstract

Singlet oxygen (1O2) 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 1O2 phosphorescence was used to determine the 1O2 quantum yields (ΦΔ) of a variety of dissolved organic matter (DOM) isolates and natural waters. In general, the 1O2 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 1O2 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 1O2 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 1O2 production, which is valuable for assessing real-world environmental behavior.