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Discussion papers
https://doi.org/10.5194/acp-2019-981
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-981
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 20 Nov 2019

Submitted as: research article | 20 Nov 2019

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

Effect of Inorganic-to-Organic Mass Ratio on the Heterogeneous OH Reaction Rates of Erythritol: Implications for Atmospheric Chemical Stability of 2-Methyltetrols

Rongshuang Xu1, Hoi Ki Lam1, Kevin R. Wilson2, James F. Davies3, Mijung Song4, Wentao Li5, Ying-Lung Steve Tse5, and Man Nin Chan1,6 Rongshuang Xu et al.
  • 1Earth System Science Programme, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
  • 2Chemical Sciences Division, LawrenceBerkeley National Laboratory, Berkeley, CA, USA
  • 3Department of Chemistry, University of California Riverside, Riverside, CA, USA
  • 4Department of Earth and Environmental Sciences, Jeonbuk National University, Jeollabuk-do, Republic of Korea
  • 5Department of Chemistry, The Chinese University of Hong Kong, Hong Kong, China
  • 6The Institute of Environment, Energy and Sustainability, The Chinese University of Hong Kong, Hong Kong, China

Abstract. 2-methyltetrols have been widely chosen as chemical tracers for isoprene-derived secondary organic aerosols. While they are often assumed to be relatively unreactive, a laboratory study reported that pure erythritol particles (an analog of 2-methyltetrols) can be heterogeneously oxidized by gas-phase OH radicals at a significant rate. This might question the efficacy of these compounds as tracers in aerosol source apportionment studies. Additional uncertainty could raise since organic compounds and inorganic salts are often coexisted in atmospheric particles. To gain more insights into the chemical stability of 2-methyltetrols in atmospheric particles, this study investigates the heterogeneous OH oxidation of pure erythritol particles and particles containing erythritol and ammonium sulfate (AS) at different dry inorganic-to-organic mass ratios (IOR) in an aerosol flow tube reactor at a high relative humidity of 85 %. The same reaction products are formed upon heterogenous OH oxidation of erythritol and erythritol-AS particles, suggesting that the reaction pathways are not strongly affected by the presence and amount of AS. On the other hand, the effective OH uptake coefficient, γeff, is found to decrease by about a factor of ~ 20 from 0.45 ± 0.025 to 0.02 ± 0.001 when the relative abundance of AS increases and the IOR increases from 0.0 to 5.0. One likely explanation is the presence of dissolved ions slows down the reaction rates by decreasing the surface concentration of erythritol and reducing the frequency of collision between erythritol and gas-phase OH radicals at the particle surface. Hence, the heterogeneous OH reactivity of erythritol and likely 2-methyltetrols in atmospheric particles would be slower than previously thought when the salts are present. Given 2-methyltetrols often coexist with a significant amount of AS in many environments, where ambient IOR can vary from ~ 1.89 to ~ 250, our kinetic data would suggest that 2-methyltetrols in atmospheric particles are likely chemically stable against heterogeneous OH oxidation under humid conditions.

Rongshuang Xu et al.
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Short summary
Atmospheric particles, a complex mixture of inorganic salts, organic compounds and water, can continually undergo heterogeneous oxidation initiated by gas-phase oxidants at the particle surface. We found that ammonium sulfate can decelerate the rate of heterogeneous OH reaction with 2-methyltetrols when the inorganic-to-organic mass ratio increases. These results would suggest 2-methyltetrols are likely chemically stable against heterogeneous OH oxidation in the atmosphere.
Atmospheric particles, a complex mixture of inorganic salts, organic compounds and water, can...
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