Predicting Reactive Intermediate Quantum Yields from Dissolved Organic Matter Photolysis Using Optical Properties and Antioxidant Capacity

Abstract

The antioxidant capacity and formation of photochemically produced reactive intermediates (RI) was studied for water samples collected from the Florida Everglades with different spatial (marsh versus estuarine) and temporal (wet versus dry season) characteristics. Measured RI included triplet excited states of dissolved organic matter (DOM*), singlet oxygen (O), and the hydroxyl radical (OH). Single and multiple linear regression modeling were performed using a broad range of extrinsic (to predict RI formation rates, R) and intrinsic (to predict RI quantum yields, Φ) parameters. Multiple linear regression models consistently led to better predictions of R and Φ for our data set but poor prediction of Φ for a previously published data set,1 probably because the predictors are intercorrelated (Pearson's r > 0.5). Single linear regression models were built with data compiled from previously published studies (n ≈ 120) in which E2:E3, S, and Φ values were measured, which revealed a high degree of similarity between RI-optical property relationships across DOM samples of diverse sources. This study reveals that OH formation is, in general, decoupled fromDOM* and O formation, providing supporting evidence that DOM* is not aOH precursor. Finally, Φ for O and DOM* correlated negatively with antioxidant activity (a surrogate for electron donating capacity) for the collected samples, which is consistent with intramolecular oxidation of DOM moieties byDOM*.

Multiple linear regression models to predict the formation efficiency of triplet excited states of dissolved organic matter in temperate wetlands

“…). These trends between and DOM bulk composition are consistent with previous reports (McCabe and Arnold ; McKay et al ). does not correlate with [DOC] ( ρ = 0.0488, p value = 0.5949), but it does correlate with both pH and [DIC] ( ρ = 0.7258 and 0.5467, respectively, both p values < 0.001; Supporting Information Fig.…”

“…S8, Section 7). This average equates to =148(±85) L mol‐photons −1 , which is a typical range observed for CDOM (Sharpless et al ; McCabe and Arnold ; McKay et al ). Experimental precision in the measurement of as assessed from the field duplicates was ≤16% ( n = 8).…”

“…A recent report using solvent and temperature adjustments to perturb DOM absorbance and fluorescence suggests that CT complexes do not form in DOM (McKay et al, ). While the hypothesis of CT complex formation has well‐founded precedent (Sharpless and Blough ), mechanisms other than formation of CT complexes may contribute to the observed trends in , including a simple screening mechanism of 3 CDOM* precursors by nontriplet forming chromophores, a disproportionate increase of nontriplet forming precursors with increasing broadband light absorption, or a complete oxidation reaction between 3 CDOM* and reduced polyphenols (McNally et al ; McKay et al ). These mechanisms may be possible alternatives to the CT hypothesis, or they may be active in combination CT complex formation.…”

“…To date, predictions have relied on the spectral properties of DOM, usually the ratio of light absorbance at 250 nm to the absorbance at 365 nm (E2/E3; typical range E2/E3 = 4–12) (Dalrymple et al ; McCabe and Arnold ; McKay et al ). This relationship is purported to exist because absorbance in the UV region is suggestive of light absorption by discreet chromophore (quantified by the absorbance at 250 nm) and absorbance in the visible and near‐UV region is suggestive of CT complex formation (quantified by the absorbance at 365 nm).…”

Understanding and predicting environmental effects on degradation of oxo-degradable polyethylene blown films

“…More specifically this effect could be that condensed water would be a carrier of dissolved organic matter (DOM) present in the soil. When exposed to sunlight, DOM is a source of reactive intermediates [Mckay et al, 2017] as described in Equation 6.1:…”