Influence of Glyoxal on the Catalytic Oxidation of S(IV) in Acidic Aqueous Media

Abstract

The role of glyoxal in S­(IV) oxidation in acidic aqueous solutions catalyzed by iron in the form of aqueous Fe3+ ions and solid iron oxide was investigated under different experimental conditions. It is found that the rate of Fe3+(aqueous (aq)) ion-catalyzed S­(IV) oxidation decreases in the presence of glyoxal. The results of mass spectral analysis and infrared spectra suggest that the trapping of SO4 – radicals, as well as the formation of glyoxal–S­(IV) adducts, are responsible for this inhibition effect. Interestingly, although sulfur oxidation is kinetically inhibited in the presence of glyoxal, S­(IV) in the form of sulfite is over time completely converted to sulfate. Additionally, the inhibition effects of glyoxal can also be observed in the reaction of S­(IV) catalyzed by iron oxide particles, albeit less than that catalyzed by dissolved Fe3+(aq). The observed inhibition effect for the iron oxide particles is proposed to be attributed to competitive surface adsorption on the iron oxide particle surface. Overall, these findings suggest that the effects of glyoxal on the catalytic oxidation of S­(IV) are highly dependent on the mechanism, form of iron (dissolved vs solid), and the ambient conditions including pH and concentration.

Field Evidence of Fe-Mediated Photochemical Degradation of Oxalate and Subsequent Sulfate Formation Observed by Single Particle Mass Spectrometry

“…First, at receptor sites similar to the one in this work, failure to consider this Fe-mediated oxalate photodegradation loss pathway has the potential to significantly overestimate the aqueous secondary organic aerosol production . Second, the influence of the oxalate–Fe complex on sulfur oxidation is likely different during nighttime when the oxalate–Fe complex may suppress the oxidation of sulfur, ,, than in the daytime when the Fe redox reaction facilitated by oxalate would produce a considerable amount of O 2 • , HO 2 , and H 2 O 2 , which is known to be an effective oxidant of S­(IV) . A recent field study found an enhanced role of transition metal ion catalysis on coarse mineral dust during in-cloud SO 2 oxidation, and emphasized its importance as a dominant in-cloud oxidation pathway .…”

“…First, at receptor sites similar to the one in this work, failure to consider this Fe-mediated oxalate photodegradation loss pathway has the potential to significantly overestimate the aqueous secondary organic aerosol production. 12 Second, the influence of the oxalate−Fe complex on sulfur oxidation is likely different during nighttime when the oxalate−Fe complex may suppress the oxidation of sulfur, 55,104,105 than in the daytime when the Fe redox reaction facilitated by oxalate would produce a considerable amount of O 2…”

Multiphase Photochemistry of Iron-Chloride Containing Particles as a Source of Aqueous Chlorine Radicals and Its Effect on Sulfate Production

“…Analogous to OH radical chemistry, oxalate production is possible from the glyoxal oxidation by Cl • . Note that glyoxal does not directly bind with Fe 3+ and hence the decay of glyoxal (Figure S17) is most likely due to its reaction with chlorine radicals. When the estimated Cl • concentration of 10 –14 M (Figure S12) is taken, the reaction rate constant of Cl • and glyoxal is calculated to be 2.4 × 10 8 M –1 s –1 (Text S6), which falls in the reported reaction rate constants of Cl • and other carbonyl compounds. , The photochemistry of aqueous particles containing both organic and inorganic compounds warrants additional investigations.…”

Organic Peroxides and Sulfur Dioxide in Aerosol: Source of Particulate Sulfate

“…38−40 All of these reactions require the formation of inorganic S(VI) species prior to reaction with reactive organic intermediates. Organosulfur species have been found to form directly from SO 2 and CC/ CO double bonds, 40−43 which can be further catalyzed by TMI, 44,45 highlighting the potential for SO 2 to directly form OS in the atmosphere.…”