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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/acp-2020-983
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-983
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  12 Oct 2020

12 Oct 2020

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This preprint is currently under review for the journal ACP.

Heterogeneous Interactions between SO2 and Organic Peroxides in Submicron Aerosol

Shunyao Wang1, Tengyu Liu2, Jinmyung Jang1, Jonathan P. D. Abbatt2, and Arthur W. H. Chan1 Shunyao Wang et al.
  • 1Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, M5S 3E5, Canada
  • 2Department of Chemistry, University of Toronto, Toronto, Ontario, M5S 3H6, Canada

Abstract. Atmospheric models often underestimate particulate sulfate, a major component in ambient aerosol, suggesting missing sulfate formation mechanisms in the models. Heterogeneous reactions between SO2 and aerosol play an important role in particulate sulfate formation and its physicochemical evolution. Here we study the reactive uptake kinetics of SO2 onto aerosol containing organic peroxides. We present chamber studies of SO2 reactive uptake performed under different relative humidities (RH), particulate peroxide contents, peroxide types, and aerosol acidities. Using different model organic peroxides mixed with ammonium sulfate particles, SO2 uptake coefficient (γSO2) was found to be exponentially dependent on RH. γSO2 increases from 10−3 at RH 25 % to 10−2 at RH 71 % as measured for a multifunctional organic peroxide. Under similar conditions, the kinetics were found to be structurally dependent: multifunctional organic peroxides have a higher γSO2 than those with only one peroxide group, consistent with the reactivity trend observed previously in the aqueous phase. In addition, γSO2 is linearly related to particle-phase peroxide content, which in turn depends on gas-particle partitioning of organic peroxides. Aerosol acidity plays a complex role in determining SO2 uptake rate, influenced by the effective Henry's Law constant of SO2 and the condensed phase kinetics of the peroxide-SO2 reaction in the highly concentrated aerosol phase. These uptake coefficients are consistently higher than those calculated from the reaction kinetics in the bulk aqueous phase, and we show experimental evidence suggesting that other factors, such as particle-phase ionic strength, can play an essential role in determining the uptake kinetics. γSO2 for different types of secondary organic aerosol (SOA) were measured to be on the order of 10−4. Overall, this study provides quantitative evidence of the multiphase reactions between SO2 and organic peroxides, highlighting the important factors that govern the uptake kinetics.

Shunyao Wang et al.

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SO2 uptake dataset Shunyao Wang https://doi.org/10.6084/m9.figshare.13078112.v1

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Short summary
Discrepancies between atmospheric modeling and field observation, especially in highly polluted cities, have highlighted the lack of understanding in sulfate formation mechanisms and/or kinetics. Here, we directly quantified the reactive uptake coefficient of SO2 onto organic peroxides, and study the important governing factors. The SO2 uptake rate was observed to depend on RH, peroxide amount and reactivity, pH, and ionic strength, which provides a framework to better predict sulfate formation.
Discrepancies between atmospheric modeling and field observation, especially in highly polluted...
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