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Title: Rapid heterogeneous oxidation of organic coatings on submicron aerosols: Heterogeneous Oxidation of Organic Aerosol
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Publication Date:
Journal Name:
Geophysical Research Letters
Page Range or eLocation-ID:
2949 to 2957
Wiley Blackwell (John Wiley & Sons)
Sponsoring Org:
National Science Foundation
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  1. Methyltetrol sulfates are unique tracers for secondary organic aerosols (SOA) formed from acid-driven multiphase chemistry of isoprene-derived epoxydiols. 2-Methyltetrol sulfate diastereomers (2-MTSs) are the dominant isomers and single most-abundant SOA tracers in atmospheric fine particulate matter (PM2.5), but their atmospheric sinks remain unknown. We investigated the oxidative aging of authentic 2-MTS aerosols by gas-phase hydroxyl radicals (•OH) at a relative humidity of 61 ± 1%. The effective rate constant for this heterogeneous reaction was determined as 4.9 ± 0.6 × 10–13 cm3 molecules–1 s–1, corresponding to an atmospheric lifetime of 16 ± 2 days (assuming an •OH concentration of 1.5more »× 106 molecules cm–3). Chemical changes to 2-MTSs were monitored by hydrophilic interaction liquid chromatography interfaced to electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (HILIC/ESI-HR-QTOFMS). Plausible reaction mechanisms are proposed for previously unknown OSs detected in atmospheric PM2.5 at mass-to-charge ratios (m/z) of 139 (C2H3O5S–), 155 (C2H3O6S–), 169 (C3H5O6S–), 171 (C3H7O6S–), 185 (C3H5O7S–), 199 (C4H7O7S–), 211 (C5H7O7S–), 213 (C5H9O7S–), 227 (C5H7O8S–), 229 (C5H9O8S–), and 231 (C5H11O8S–). Heterogeneous •OH oxidation of 2-MTSs redistributes the particulate sulfur speciation into more oxygenated/functionalized OSs, likely modifying the aerosol physicochemical properties of SOA containing 2-MTSs.« less
  2. 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