Quantifying the effects of mixing state on aerosol optical properties
<p>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 s...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/9265/2022/acp-22-9265-2022.pdf |
| Summary: | <p>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 <span class="inline-formula">−22.3</span> % with a median of <span class="inline-formula">−0.9</span> %. The
mixing state metric <span class="inline-formula"><i>χ</i></span> 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 <span class="inline-formula"><i>χ</i></span>. 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 <span class="inline-formula"><i>χ</i></span>. These results are
further evidence of the important yet complicated role of mixing state
in calculating aerosol optical properties.</p> |
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| ISSN: | 1680-7316 1680-7324 |