Preprints
https://doi.org/10.5194/acp-2021-17
https://doi.org/10.5194/acp-2021-17

  05 Feb 2021

05 Feb 2021

Review status: a revised version of this preprint is currently under review for the journal ACP.

Estimation of Secondary Organic Aerosol Viscosity from Explicit Modeling of Gas-Phase Oxidation of Isoprene and α-pinene

Tommaso Galeazzo1, Richard Valorso2, Ying Li1, Marie Camredon2, Bernard Aumont2, and Manabu Shiraiwa1 Tommaso Galeazzo et al.
  • 1Department of Chemistry, University of California, Irvine, CA92625, USA
  • 2LISA, CNRS/INSU UMR7583, Université Paris Est Créteil et Université Paris Diderot, Institut Pierre Simon Laplace, 94010 Créteil, France

Abstract. Secondary organic aerosols (SOA) are major components of atmospheric fine particulate matter, affecting climate and air quality. Mounting evidence exists that SOA can adopt glassy and viscous semisolid states, impacting formation and partitioning of SOA. In this study, we conduct explicit modeling of isoprene photooxidation and α-pinene ozonolysis and subsequent SOA formation using the GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere) model. Our recently-developed parameterizations to predict glass transition temperature of organic compounds are implemented into a box model with explicit gas-phase chemical mechanisms to simulate viscosity of SOA. The effects of chemical composition, relative humidity, mass loadings and mass accommodation on particle viscosity are investigated in comparison with measurements of SOA viscosity. The simulated viscosity of isoprene SOA agrees well with viscosity measurements as a function of relative humidity, while the model underestimates viscosity of α-pinene SOA by a few orders of magnitude. This difference may be due to missing processes in the model including gas-phase dimerization and particle-phase reactions leading to the formation of high molar mass compounds that would increase particle viscosity. Additional simulations imply that kinetic limitations of bulk diffusion and reduction in mass accommodation coefficient may also play a role in enhancing particle viscosity by suppressing condensation of semi-volatile compounds. The developed model is a useful tool for analysis and investigation of the interplay among gas-phase reactions, particle chemical composition and SOA phase state.

Tommaso Galeazzo et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Referee comment on acp-2021-17', Anonymous Referee #1, 03 Mar 2021
  • RC2: 'Comment on acp-2021-17', Anonymous Referee #2, 03 Mar 2021

Tommaso Galeazzo et al.

Tommaso Galeazzo et al.

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Short summary
We simulate SOA viscosity with explicit modeling of gas-phase oxidation of isoprene and α-pinene. While the viscosity dependence on relative humidity and mass loadings is captured well by simulations, the model underestimates measured viscosity indicating missing processes. Kinetic limitations and reduction in mass accommodation may cause an increase of viscosity. The developed model is powerful for investigation of the interplay among gas reactions, chemical composition and phase state.
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