Importance of Sulfate Radical Anion Formation and Chemistry in Heterogeneous OH Oxidation of Sodium Methyl Sulfate, the Smallest Organosulfate

Abstract

Abstract.Organosulfates are important organosulfur compounds present in atmospheric particles. While the abundance, 10 composition, and formation mechanisms of organosulfates have been extensively investigated, it remains unclear how they transform and evolve throughout their atmospheric lifetime. To acquire a fundamental understanding of how organosulfates chemically transform in the atmosphere, this work investigates the heterogeneous OH radical-initiated oxidation of sodium methyl sulfate (CH 3 SO 4 Na) droplets, the smallest organosulfate detected in atmospheric particles, using an aerosol flow tube reactor at a high relative humidity of 85 %. Aerosol mass spectra measured by a soft atmospheric pressure ionization source 15 (Direct Analysis in Real Time, DART) coupled with a high-resolution mass spectrometer showed that neither functionalization nor fragmentation products are detected. Instead, the ion signal intensity of the bisulfate ion (HSO 4 − ) has been found to increase significantly after OH oxidation. We postulate that sodium methyl sulfate tends to fragment into a formaldehyde (CH 2 O) and a sulfate radical anion (SO 4•− ) upon OH oxidation. The formaldehyde is likely partitioned back to the gas phase due to its high volatility. The sulfate radical anion, similar to OH radical, can abstract a hydrogen atom from 20 neighboring sodium methyl sulfate to form the bisulfate ion, contributing to the secondary chemistry. Kinetic measurements show that the heterogeneous OH reaction rate constant, k, is (3.79 ± 0.19) × 10 -13 cm 3 molecule -1 s -1 with an effective OH uptake coefficient, γ eff , of 0.17 ± 0.03. While about 40 % of sodium methyl sulfate is being oxidized at the maximum OH exposure (1.27 × 10 12 molecule cm −3 s), only a 3 % decrease in particle diameter is observed. This can be attributed to a small fraction of particle mass lost via the formation and volatilization of formaldehyde. Overall, we firstly demonstrate that 25 the heterogeneous OH oxidation of an organosulfate can lead to the formation of sulfate radical anion and produce inorganic sulfate. Fragmentation processes and sulfate radical anion chemistry play a key role in determining the compositional evolution of sodium methyl sulfate during heterogeneous OH oxidation. 35Atmos. Chem. Phys. Discuss., https://doi

Radical oxidation of methyl vinyl ketone and methacrolein in aqueous droplets: Characterization of organosulfates and atmospheric implications

“…Formation of organosulfates Based on 2009 (Hallquist et al, 2009), 2011 (Ervens et al, 2011) and 2015 (Nozière et al, 2015) review papers, aqSOA samples containing organosulfates can be produced in a laboratory framework through in-cloud chemistry under dark and/or solar conditions. In the dark mode two atmospherically relevant pathways have been suggested: (1) addition of the sulfate radicals onto an unsaturated C=C bond of the precursor (Szmigielski, 2016;Kwong et al, 2018), (2) nucleophilic addition of the sulfate anion onto an isoprene-derived epoxy ring (Darer et al, 2011;Nguyen et al, 2014). In contrast, solar approaches have entailed (1) UV irradiation of concentrated solutions of ammonium sulfate and the organic precursor (Nozière et al, 2010), (2) laser photolysis of concentrated solutions containing sulfate peroxide and carbonyl precursors (Schindelka et al, 2013).…”

Growth Mechanisms of Nano-to Micro-Sized Lead Sulfate Particles

“…Additionally, acetone is a polar aprotic solvent, meaning that it cannot donate protons (H + ) since it lacks a hydroxyl group, which sets it apart from the other alcohols. 27 This lack of hydrogen donation in the acetone leads to less interaction with the anions (SO 4 –2 ) in the solution. Also, the oxygen in the carbonyl group can interact via hydrogen bonding with water that surrounds the nanoparticles, cations, and anions in the solution, which is related to desolvation described above.…”

“…Since methanol has a hydroxyl group, it can donate a proton, thus increasing the interaction with anions in the solution and at the liquid/particle interface. 27 This increased anion interaction will hinder the nucleation of nanoparticles and interaction at their surface by reducing cation interaction. Also, since it is a longer chain, there is a slight decrease in the solubility of methanol with water.…”

“…Microparticles were not seen at mixing times below 5 min most likely due to the hydroxyl group increasing the interaction with anions in the solution and at the liquid/particle interface similar to methanol. 27 Also, ethanol has an additional alkyl group in the chain compared to methanol, which also makes it slightly larger than methanol. This additional alkyl group also makes the chain less reactive with water, which can be related to reduced formation of microparticles at lower intervals of mixing times.…”

Interactions of organosulfates with water vapor under sub- and supersaturated conditions

“…where ρ0 and ρw are the density of the dry sample and water, respectively. The density of methyl-, ethyl-and octyl-OS particles were reported to be 1.60, 1.46 and 1.19 g cm -3 with an uncertainty of 20-30% (Kwong et al, 2018;ChemistryDashboard, 2021). Figure 6 compares VSA-derived GFs and those measured using H-TDMA for methyl-, ethyl-and octyl-OS, and it can be concluded that for RH at which samples used in the VSA experiments were deliquesced, GFs derived from mass change measured using VSA agree relatively well with those directly measured using H-TDMA.…”