Dissolved organic matter singlet oxygen quantum yields: Evaluation using time-resolved singlet oxygen phosphorescence.

Singlet oxygen (O-1(2)) 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( 1)O(2 ) phosphorescence was used to determine the O-1(2) quantum yields (Phi(Delta)) of a variety of dissolved organic matter (DOM) isolates and natural waters. In general, the O-1(2) 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-1(2) quantum yields, an interesting result given that these fractions are not retained in typical hurnic and fulvic acid isolation procedures that use XAD resins. The excitation wavelength dependence of O-1(2) 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-1(2) production, which is valuable for assessing real-world environmental behavior.