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Title: Increasing Isoprene Epoxydiol-to-Inorganic Sulfate Aerosol (IEPOX:Sulf inorg ) Ratio Results in Extensive Conversion of Inorganic Sulfate to Organosulfur Forms: Implications for Aerosol Physicochemical Properties
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  1. In order to examine the reaction products, kinetics, and implications of ISOPOOH with aqueous sulfite, ammonium bisulfate particles were injected into the UNC 10‐m3 indoor environmental chamber under humid (i.e., 72% RH) and dark conditions. After the inorganic sulfate concentration stabilized, selected concentrations of gas‐phase 1,2‐ISOPOOH were injected into the chamber, and aerosols showed a minimal mass increase. Gaseous SO2 was subsequently injected into the chamber and a significant amount of aerosol mass was produced. The gas‐phase ISOPOOH and particle‐phase species were sampled with online instruments, including a chemical ionization mass spectrometer (CIMS), an aerosol chemical speciation monitor (ACSM), amore »particle‐into‐liquid sampler (PILS) for analysis by ion chromatography analysis (IC), and filter samples were analyzed by an ultra‐performance liquid chromatography coupled to an electrospray ionization highresolution quadrupole time‐of‐flight mass spectrometry (UPLCESI‐ HR‐QTOFMS) to obtain offline molecular‐level information. Results show that a significant amount of inorganic sulfate and organosulfates were formed rapidly after injecting SO2, altering the chemical and physical properties of the particles including phase state, pH, reactivity, and composition. Multifunctional C5‐organic species that were previously measured in atmospheric fine aerosol samples were also reported here as reaction products, including 2‐methyletrols and 2‐methyltetrol sulfates that were previously thought to be only produced from the reactive uptake of isoprene‐derived epoxydiols (IEPOX). Such results indicate that the multiphase reactions of ISOPOOH could have significant impacts on the atmospheric lifecycle of organic aerosols and sulfur, as well as the physicochemical properties of ambient particles.« less
  2. Abstract. Air quality models have not been able to reproduce the magnitude of theobserved concentrations of fine particulate matter (PM2.5) duringwintertime Chinese haze events. The discrepancy has been at least partlyattributed to low biases in modeled sulfate production rates, due to the lackof heterogeneous sulfate production on aerosolsin the models. In this study, we explicitly implement four heterogeneous sulfate formationmechanisms into a regional chemical transport model, in addition togas-phase and in-cloud sulfate production. We compare the model results withobservations of sulfate concentrations and oxygen isotopes, Δ17O(SO42-), in the winter of 2014–2015, the latter of whichis highly sensitive to the relative importance ofmore »different sulfateproduction mechanisms. Model results suggest that heterogeneous sulfateproduction on aerosols accounts for about 20 % of sulfate production inclean and polluted conditions, partially reducing the modeled low bias insulfate concentrations. Model sensitivity studies in comparison with theΔ17O(SO42-) observations suggest that heterogeneoussulfate formation is dominated by transition metal ion-catalyzed oxidation of SO2.« less
  3. Abstract. Acid-catalyzed multiphase chemistry of epoxydiols formed from isopreneoxidation yields the most abundant organosulfates (i.e., methyltetrolsulfates) detected in atmospheric fine aerosols in the boundary layer. Thispotentially determines the physicochemical properties of fine aerosols inisoprene-rich regions. However, chemical stability of these organosulfatesremains unclear. As a result, we investigate the heterogeneous oxidation ofaerosols consisting of potassium 3-methyltetrol sulfate ester(C5H11SO7K) by gas-phase hydroxyl (OH) radicals at a relativehumidity (RH) of 70.8 %. Real-time molecular composition of the aerosolsis obtained by using a Direct Analysis in Real Time (DART) ionization sourcecoupled to a high-resolution mass spectrometer. Aerosol mass spectra revealthat 3-methyltetrol sulfate ester can bemore »detected as its anionic form(C5H11SO7-) via direct ionization in the negativeionization mode. Kinetic measurements reveal that the effective heterogeneousOH rate constant is measured to be 4.74±0.2×10-13 cm3 molecule−1 s−1 with a chemical lifetime against OHoxidation of 16.2±0.3 days, assuming an OH radical concentration of1.5×106 molecules cm−3. Comparison of this lifetime withthose against other aerosol removal processes, such as dry and wetdeposition, suggests that 3-methyltetrol sulfate ester is likely to bechemically stable over atmospheric timescales. Aerosol mass spectra only showan increase in the intensity of bisulfate ion (HSO4-) afteroxidation, suggesting the importance of fragmentation processes. Overall,potassium 3-methyltetrol sulfate ester likely decomposes to form volatilefragmentation products and aqueous-phase sulfate radial anion(SO4⚫-). SO4⚫- subsequently undergoesintermolecular hydrogen abstraction to form HSO4-. These processesappear to explain the compositional evolution of 3-methyltetrol sulfate esterduring heterogeneous OH oxidation.« less