Preprints
https://doi.org/10.5194/acp-2022-131
https://doi.org/10.5194/acp-2022-131
 
02 Mar 2022
02 Mar 2022
Status: this preprint is currently under review for the journal ACP.

Quantifying the effects of mixing state on aerosol optical properties

Yu Yao1, Jeffrey Curtis2, Joseph Ching3,4,5, Zhonghua Zheng6,7,8, and Nicole Riemer1 Yu Yao et al.
  • 1Department of Atmospheric Sciences, University of Illinois Urbana-Champaign, Urbana, IL, 61801, USA
  • 2Department of Mechanical Science and Engineering, University of Illinois Urbana-Champaign, Urbana, IL, 61801, USA
  • 3Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Ibaraki, 305-0052, Japan
  • 4National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo, 190-8518, Japan
  • 5Research Institute for Humanity and Nature, 457-4 Motoyama, Kamigamo, Kita-ku, Kyoto, 603-8047, Japan
  • 6Computational and Information Systems Laboratory, National Center for Atmospheric Research, Boulder, CO, 80307, USA
  • 7Climate and Global Dynamics Laboratory, National Center for Atmospheric Research, Boulder, CO, 80307, USA
  • 8Advanced Study Program, National Center for Atmospheric Research, Boulder, CO, 80307, USA

Abstract. Calculations of the aerosol direct effect on climate rely on simulated aerosol fields. The model representation of aerosol mixing state potentially introduces large uncertainties into these calculations, since the simulated aerosol optical properties are sensitive to mixing state. In this study, we systematically quantified the impact of aerosol mixing state on aerosol optical properties using an ensemble of 1800 aerosol populations from particle-resolved simulations as a basis for Mie calculations for optical properties. Assuming the aerosol to be internally mixed within prescribed size bins caused overestimations of aerosol absorptivity and underestimations of aerosol scattering. Together, these led to errors in the populations' single scattering albedo of up to -22.3 % with a median of -0.9 %. The mixing state metric χ proved useful in relating errors in the volume absorption coefficient, the volume scattering coefficient and the single scattering albedo to the degree of internally mixing of the aerosol, with larger errors being associated with more external mixtures. At the same time, a range of errors existed for any given value of χ. We attributed this range to the extent to which the internal mixture assumption distorted the particles' black carbon content and the refractive index of the particle coatings. Both can vary for populations with the same value of χ. These results are further evidence of the important yet complicated role of mixing state in calculating aerosol optical properties.

Yu Yao et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-131', Anonymous Referee #1, 22 Mar 2022
  • RC2: 'Comment on acp-2022-131', Anonymous Referee #2, 30 Mar 2022

Yu Yao et al.

Data sets

Data for: Quantifying the effects of mixing state on aerosol optical properties Yao, Yu; Curtis, Jeffrey; Ching, Joseph; Zheng, Zhonghua; Riemer, Nicole https://doi.org/10.13012/B2IDB-8157303_V1

Model code and software

PartMC: Particle-resolved Monte Carlo code for atmospheric aerosol simulation Nicole Riemer and Matthew West https://doi.org/10.5281/zenodo.5644422

Yu Yao et al.

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Short summary
Investigating the impacts of aerosol mixing state on aerosol optical properties has a long history from both the modeling and experimental perspective. In this study, we used particle-resolved simulations as a benchmark to determine the error in optical properties when using simplified aerosol representations. We found that errors in single scattering albedo due to the internal mixture assumptions can have substantial effects in calculating aerosol direct radiative forcing.
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