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Cited by 15Atmospheric aerosols and cloudsClimate Change and GeoengineeringAtmospheric chemistry and aerosols

Limitations of assuming internal mixing between different aerosol species: a case study with sulfate geoengineering simulations

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Visioni, Daniele, Tilmes, Simone, Bardeen, Charles, Mills, Michael, MacMartin, Douglas G., Kravitz, Ben, Richter, Jadwiga H.·2022·Atmospheric Chemistry and Physics
DOI 10.5194/acp-22-1739-2022

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Abstract

Simulating the complex aerosol microphysical processes in a comprehensive Earth system model can be very computationally intensive; therefore many models utilize a modal approach, where aerosol size distributions are represented by observation-derived lognormal functions, and internal mixing between different aerosol species within an aerosol mode is often assumed. This approach has been shown to yield satisfactory results across a large array of applications, but there may be cases where the simplification in this approach may produce some shortcomings. In this work we show specific conditions under which the current approximations used in some modal approaches might yield incorrect answers. Using results from the Community Earth System Model v1 (CESM1) Geoengineering Large Ensemble (GLENS) project, we analyze the effects in the troposphere of a continuous increasing load of sulfate aerosols in the stratosphere, with the aim of counteracting the surface warming produced by non-mitigated increasing greenhouse gas (GHG) concentrations between 2020–2100. We show that the simulated results pertaining to the evolution of sea salt and dust aerosols in the upper troposphere are not realistic due to internal mixing assumptions in the modal aerosol treatment, which in this case reduces the size, and thus the settling velocities, of those particles and ultimately changes their mixing ratio below the tropopause. The unnatural increase of these aerosol species affects, in turn, the simulation of upper tropospheric ice formation, resulting in an increase in ice clouds that is not due to any meaningful physical mechanisms. While we show that this does not significantly affect the overall results of the simulations, we point to some areas where results should be interpreted with care in modeling simulations using similar approximations: in particular, in the evolution of upper tropospheric clouds when large amounts of sulfate are present in the stratosphere, as after a large explosive volcanic eruption or in similar stratospheric aerosol injection cases. Finally, we suggest that this can be avoided if sulfate aerosols in the coarse mode, the predominant species in these situations, are treated separately from other aerosol species in the model.

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  • MAM4 uses assumptions of internal mixing for the size distribution of different species, whereas mass is tracked separately.

    “However, MAM4 uses assumptions of internal mixing for the size distribution of different species, whereas mass is tracked separately (Visioni et al., 2022).”

    From Air quality impacts of stratospheric aerosol injections are likely small and mainly driven by changes in climate, not aerosol settling (2026) · cites this paper as Visioni et al., 2022

    Section 2.1 describes internal mixing within each mode and conservation of mass for individual species; Section 3 says species share a size distribution while their mass concentrations are calculated separately. But these passages describe MAM3, not the MAM4 named in the claim. The copy does not establish that MAM4 uses the same treatment. (LLM, conf=0.88)

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Research works printed but not linked: 3

  1. Seinfeld, J. H. and Pandis, S. N.: Atmospheric chemistry and physics: from air pollution to climate change, John Wiley & Sons, ISBN 978-1-118-94740-1, 2016. a, b, c
  2. Tilmes, S., Richter, J. H., Mills, M., Kravitz, B., and MacMartin, D. G.: Stratospheric Aerosol Geoengineering Large Ensemble Project – GLENS, NCAR​​​​​​​ [data set], https://doi.org/10.5065/D6JH3JXX, 2018c. a · DOI
  3. Visioni, D. and MacMartin, D. G.: Data from: Is Turning Down the Sun a Good Proxy for Stratospheric Sulfate Geoengineering?, Cornell University Library [data set], https://doi.org/10.7298/z8c9-3p43, 2021. a · DOI

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Authors
Visioni, D., Tilmes, S., Bardeen, C., Mills, M., MacMartin, D. G., Kravitz, B., & Richter, J. H.
Affiliations
  • Cornell University (US)
  • NSF National Center for Atmospheric Research (US)
  • Pacific Northwest National Laboratory (US)
Corresponding author
  • Visioni, Daniele
  • Tilmes, Simone
  • Mills, Michael
  • MacMartin, Douglas G.
  • Kravitz, Ben
ORCID
Venue
Atmospheric Chemistry and Physics
Publisher
Copernicus GmbH
Published
2022-02-04
Volume
22
Issue
3
Pages
1739-1756
ISSN
  • 1680-7316 (ISSN-L)
  • 1680-7324
DOI
10.5194/acp-22-1739-2022
OpenAlex
W4210609685
Cited by
15
References
70
Citations by year
2026: 1 · 2025: 3 · 2023: 6 · 2022: 5
FWCI
1.39
Type
journal article
Language
en
Open access
Licence
Locations
  • Atmospheric chemistry and physics (publishedVersion, cc-by)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
  • National Science Foundation (CBET-1818759, CBET-1931641)
  • Cornell Atkinson Center for Sustainability, Cornell University (n/a)
Topics
  • Physical Sciences › Environmental Science › Global and Planetary Change › Atmospheric aerosols and clouds
  • Physical Sciences › Environmental Science › Global and Planetary Change › Climate Change and Geoengineering
  • Physical Sciences › Earth and Planetary Sciences › Atmospheric Science › Atmospheric chemistry and aerosols
Keywords
internal mixing, aerosol mixing ratio, stratospheric aerosol injection, sea salt aerosol, dust aerosols, settling velocity, explosive eruptions, aerosol microphysics

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