Abstract
Singlet oxygen (1O2) is a reactive oxygen species produced in sunlit waters via energy transfer from the triplet states of natural sensitizers. There has been an increasing interest in measuring apparent 1O2 quantum yields (ΦΔ) of aquatic and atmospheric organic matter samples, driven in part by the fact that this parameter can be used for environmental fate modeling of organic contaminants and to advance our understanding of dissolved organic matter photophysics. However, the lack of reproducibility across research groups and publications remains a challenge that significantly limits the usability of literature data. In the first part of this review, we critically evaluate the experimental techniques that have been used to determine ΦΔ values of natural organic matter, we identify and quantify sources of errors that potentially explain the large variability in the literature, and we provide general experimental recommendations for future studies. In the second part, we provide a qualitative overview of known ΦΔ trends as a function of organic matter type, isolation and extraction procedures, bulk water chemistry parameters, molecular and spectroscopic organic matter features, chemical treatments, wavelength, season, and location. This review is supplemented with a comprehensive database of ΦΔ values of environmental samples.
Highlights
Singlet oxygen (1O2) is a photochemically produced reactive intermediate (PPRI) and an important oxidant ubiquitous in sunlit aquatic environments
Apparent quantum yields can be used to study and compare the sensitizing properties of natural chromophores based on their origin[8,32−39] and to understand the effect of environmental factors on the photoreactivity of dissolved organic matter.[40−43] the study of ΦΔ values offers the prospect of deepening our understanding of basic photophysical properties of DOM
We report ΦΔ values for Suwannee River fulvic acid (SRFA) and Pony Lake fulvic acid (PLFA) to provide a better sense of the variability observed under comparable experimental conditions. bSome measurements were performed via a reference chemical probe method (Table S8). cUnclear if authors used radiometry or chemical actinometry. dExceptions of the general trend ΦΔSRFA < ΦΔPLFA
Summary
Singlet oxygen (1O2) is a photochemically produced reactive intermediate (PPRI) and an important oxidant ubiquitous in sunlit aquatic environments. A useful parameter in this respect is the apparent singlet oxygen quantum yield (ΦΔ), which represents the moles of 1O2 produced per moles of photons absorbed by a sensitizer (eq 1). In this context, the term “apparent” indicates that the actual sensitizer(s) responsible for of the complex. Apparent quantum yields of PPRIs, including 1O2, are needed as the input parameters in predictive models of steady-state concentrations and micropollutants’ lifetimes.[2,30,31] apparent quantum yields can be used to study and compare the sensitizing properties of natural chromophores based on their origin (i.e., microbially vs terrestrially derived DOM)[8,32−39] and to understand the effect of environmental factors (e.g., photooxidation) on the photoreactivity of dissolved organic matter.[40−43] the study of ΦΔ values offers the prospect of deepening our understanding of basic photophysical properties of DOM
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