Inorganic Sulfur Species Formed upon Heterogeneous OH Oxidation of Organosulfates: A Case Study of Methyl Sulfate

Abstract

Recent studies reveal that organosulfates at the particle surface can be oxidized by gas-phase OH radicals with significant rates. Inorganic sulfur species, such as the bisulfate ion (HSO 4 − ) and sulfate ion (SO 4 2− ), can be formed upon these heterogeneous oxidation processes through the formation and subsequent reactions of sulfate radical anion (SO 4 •− ) in the particle phase. However, the amount of inorganic sulfur species produced in these heterogeneous oxidation reactions is not known. We investigate the heterogeneous OH oxidation of sodium methyl sulfate (CH 3 SO 4 Na), the smallest organosulfate detected in atmospheric particles, using an oxidation flow reactor at a relative humidity of 75 %. We quantify the kinetics by measuring the decay of CH 3 SO 4 Na and the amount of HSO 4 − and SO 4 2− formed upon oxidation using ion chromatography. Kinetic measurements determine the heterogeneous OH reaction rate to be (5.72 ± 0.14) × 10 −13 cm 3 molecule −1 s −1 , with an effective OH uptake coefficient, γ eff , of 0.31 ± 0.06. The molar yield of inorganic sulfur species, defined as the total number of moles of HSO 4 − and SO 4 2− formed per mole of CH 3 SO 4 Na consumed upon oxidation, is found to be significant and has an average value of 0.62 ± 0.18 upon oxidation. A kinetic model is developed to describe the kinetics and inorganic sulfur species formation upon oxidation. Model simulations suggest that CH 3 SO 4 Na tends to decompose rapidly into formaldehyde and SO 4•−, and the reaction of SO 4•− with CH 3 SO 4 Na plays a significant role in both governing the kinetics and the formation of inorganic sulfur species.

T- and pH-Dependent Kinetics of the Reactions of ·OH(aq) with Glutaric and Adipic Acid for Atmospheric Aqueous-Phase Chemistry

“…Hydroxyl radicals (·OH) are important oxidants in the atmospheric environment. − In the aqueous phase, OH radicals can be formed from various sources including uptake from the gas phase, the Fenton reaction of H 2 O 2 with Fe 2+ , photolysis of H 2 O 2 , etc. , In the aqueous phases of aerosols and cloud droplets, the OH radicals can react with glutaric acid (HOOC­(CH 2 ) 3 COOH) and adipic acid (HOOC­(CH 2 ) 4 COOH) by H atom abstraction . The alkyl radicals formed can then generate higher level oxidation products in the presence of oxygen. , In addition, an electron transfer reaction also can occur between the deprotonated carboxyl group and ·OH. , Based on the speciation calculation, glutaric acid and adipic acid are fully protonated (H 2 A) when the pH value is lower than 2 and are fully deprotonated (A 2– ) when the pH value is higher than 8. , In previous studies, the OH radical reaction rate constants of the two DCAs in the H 2 A and A 2– forms have been determined at room temperature at pH values of 2 and 9 by Scholes and Willson and Herrmann .…”

Single-particle Raman spectroscopy for studying physical and chemical processes of atmospheric particles

“…(Yu et al, 2018) The synergy of NO2 and O2, which involved mechanisms such as chain reactions, resulted in much faster sulfate formation than the sum of the reaction rates with NO2 and with O2 alone. These reports show the usefulness of single-particle Raman spectroscopy in studying the multiphase formation of particulate (Xu et al, 2020b) and organo-sulfate functional groups are also Raman-active. (Bondy et al, 2018) Raman spectroscopy may find applications in the study of organo-sulfates.…”

Chemical transformation of a long-chain alkyl organosulfate via heterogeneous OH oxidation: a case study of sodium dodecyl sulfate

“…Importantly, several unidentified OS can be explained, in respect of formation mechanisms, by heterogeneous OH oxidation of OS. 54,57 Regarding the formation of other products, Xu et al 56 reported the significant molar yield of inorganic sulfates from methyl OS, defined as the numbers of moles of bisulfate (HSO 4 -) and sulfate (SO 4 -) ions generated per mole of parent OS reacted, to be mounted up to (62 ± 18) % upon heterogeneous OH oxidation. From these findings, it is reasonable to hypothesize that a portion of OS may not be as atmospherically stable species as previously presumed.…”