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Discussion papers
https://doi.org/10.5194/acp-2018-989
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-989
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 23 Oct 2018

Research article | 23 Oct 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Heterogeneous OH Oxidation of Isoprene Epoxydiol-Derived Organosulfates: Kinetics, Chemistry and Formation of Inorganic Sulfate

Hoi Ki Lam1, Kai Chung Kwong1, Hon Yin Poon1, James F. Davies2, Zhenfa Zhang3, Avram Gold3, Jason D. Surratt3, and Man Nin Chan1,4 Hoi Ki Lam et al.
  • 1Earth System Science Programme, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
  • 2Department of Chemistry, UC Riverside, Riverside, USA
  • 3Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, The University of North Carolina at Chapel Hill, Chapel Hill, USA
  • 4The Institute of Environment, Energy and Sustainability, The Chinese University of Hong Kong, Hong Kong, China

Abstract. Acid-catalyzed multiphase chemistry of epoxydiols formed from isoprene oxidation yields the most abundant organosulfates (i.e., methyltetrol sulfates) detected in atmospheric fine aerosols. This potentially determines the physicochemical properties of fine aerosols in isoprene-rich regions. However, chemical stability of these organosulfates remains unclear. As a result, we investigate the heterogeneous oxidation of aerosols consisting of potassium 3-methyltetrol sulfate ester (C5H11SO7K) by gas-phase hydroxyl (OH) radicals through studying the oxidation kinetics and reaction products at a relative humidity (RH) of 70.8%. Real-time molecular composition of the aerosols is obtained by using a Direct Analysis in Real Time (DART) ionization source coupled to a high-resolution mass spectrometer. Aerosol mass spectra reveal that 3-methyltetrol sulfate ester can be detected as its anionic form (C5H11SO7) via direct ionization in the negative ionization mode. Kinetic measurements reveal that the effective heterogeneous OH rate constant is measured to be 4.74±0.2×10−13cm3molecule−1s−1 with a chemical lifetime against OH oxidation of 16.2±0.3days. Comparison of this lifetime with those against other aerosol removal processes, such as dry and wet deposition, suggests that 3-methyltetrol sulfate ester is likely to be chemically stable over atmospheric timescales. Aerosol mass spectra only show an increase in the intensity of bisulfate ion (HSO4) after oxidation, suggesting the absence of functionalization processes is likely attributable to the steric effect of substituted functional groups (e.g. methyl, alcohol and sulfate groups) on peroxy–peroxy radical reactions. Overall, potassium 3-methyltetrol sulfate ester likely decomposes to form volatile fragmentation products and aerosol-phase sulfate radial anion (SO4•−). SO4•− subsequently undergoes intermolecular hydrogen abstraction to form HSO4. These processes appear to explain the compositional evolution of 3-methyltetrol sulfate ester during heterogeneous OH oxidation.

Hoi Ki Lam et al.
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Short summary
Organosulfates are ubiquitous in the atmosphere. We find that chemical transformation of IEPOX-derived organosulfates, one of the most abundant organosulfates, through heterogeneous OH oxidation can generate inorganic sulfate. The findings of this work provide new reaction pathways for recycling of inorganic and organic sulfur and may suggest that organosulfates could be reservoirs of inorganic sulfates in the atmosphere.
Organosulfates are ubiquitous in the atmosphere. We find that chemical transformation of...
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