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Discussion papers
https://doi.org/10.5194/acp-2020-82
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-82
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 05 Feb 2020

Submitted as: research article | 05 Feb 2020

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This preprint is currently under review for the journal ACP.

Heterogeneous oxidation of amorphous organic aerosol surrogates by O3, NO3, and OH at typical tropospheric temperatures

Jienan Li, Seanna M. Forrester, and Daniel A. Knopf Jienan Li et al.
  • School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794-5000, USA

Abstract. Typical tropospheric temperatures render possible phase states of amorphous organic aerosol (OA) particles to solid, semi-solid and liquid. This will affect the multiphase oxidation kinetics involving the organic condensed phase and gaseous oxidants and radicals. To quantify this effect, we determined the reactive uptake coefficients (γ) of O3, NO3 and OH by substrate films composed of single and binary OA surrogate species under dry conditions for temperatures from 213 to 313 K. A temperature-controlled coated-wall flow reactor coupled to a chemical ionization mass spectrometer was applied to determine γ with consideration of gas diffusion transport limitation and gas flow entrance effects, which can impact heterogeneous reaction kinetics. The phase state of the organic substrates was probed via the poke-flow technique, allowing the estimation of the substrates’ glass transition temperatures. γ values for O3 and OH uptake to a canola oil substrate, NO3 uptake to a levoglucosan and a levoglucosan/xylitol substrate, and OH uptake to a glucose and glucose/1,2,6-hexanetriol substrate have been determined as a function of temperature. We observed the greatest changes in γ with temperature for substrates that experienced the largest changes in viscosity as a result of a solid-to-liquid phase transition. Organic substrates that maintain a semi-solid or solid phase state and as such a relatively higher viscosity, do not display large variations in heterogeneous reactivity. From 213 K to 293 K, γ values of O3 with canola oil, of NO3 with a levoglucosan/xylitol mixture, and of OH with a glucose/1,2,6-hexanetriol mixture and canola oil, increase by about a factor of 34, 3, 2 and 5, respectively, due to a solid-to-liquid phase transition of the substrate. These results demonstrate that the surface and bulk lifetime of the OA surrogate species can significantly increase due to the slowed heterogeneous kinetics when OA species are solid or highly viscous in the middle and upper troposphere. This experimental study will further our understanding of the chemical evolution of OA particles with subsequent important consequences for source apportionment, air quality, and climate.

Jienan Li et al.

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Latest update: 18 Feb 2020
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Short summary
Organic aerosol is ubiquitous in the atmosphere and can change its phase state from liquid to solid in response to temperature. Our laboratory measurements demonstrate that the chemical reactivity of typical organic aerosol species with atmospheric oxidants is modulated by the species’ phase state. We find that under temperatures typical of the middle and upper troposphere the chemical lifetime of organic aerosol can be significantly extended due to the reduced reactive uptake of gas oxidants.
Organic aerosol is ubiquitous in the atmosphere and can change its phase state from liquid to...
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