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| Titel |
Perturbations of the optical properties of mineral dust particles by mixing with black carbon: a numerical simulation study |
| VerfasserIn |
B. V. Scarnato, S. China, K. Nielsen, C. Mazzoleni |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 12 ; Nr. 15, no. 12 (2015-06-25), S.6913-6928 |
| Datensatznummer |
250119849
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| Publikation (Nr.) |
 copernicus.org/acp-15-6913-2015.pdf |
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| Zusammenfassung |
Field observations show that individual aerosol particles are a complex
mixture of a wide variety of species, reflecting different sources and
physico-chemical transformations. The impacts of
individual aerosol morphology and mixing characteristics on the Earth system
are not yet fully understood. Here we present a sensitivity study on
climate-relevant aerosols optical properties to various approximations. Based
on aerosol samples collected in various geographical locations, we have
observationally constrained size, morphology and mixing, and accordingly
simulated, using the discrete dipole approximation model (DDSCAT), optical
properties of three aerosols types: (1) bare black carbon (BC) aggregates,
(2) bare mineral dust, and (3) an internal mixture of a BC aggregate laying
on top of a mineral dust particle, also referred to as polluted dust.
DDSCAT predicts optical properties and their spectral dependence consistently
with observations for all the studied cases. Predicted values of mass
absorption, scattering and extinction coefficients (MAC, MSC, MEC) for bare
BC show a weak dependence on the BC aggregate size, while the asymmetry
parameter (g) shows the opposite behavior. The simulated optical properties
of bare mineral dust present a large variability depending on the modeled
dust shape, confirming the limited range of applicability of spheroids over
different types and size of mineral dust aerosols, in agreement with previous
modeling studies. The polluted dust cases show a strong decrease in MAC
values with the increase in dust particle size (for the same BC size) and
an increase of the single scattering albedo (SSA). Furthermore, particles with
a radius between 180 and 300 nm are characterized by a decrease in SSA values
compared to bare dust, in agreement with field observations.
This paper demonstrates that observationally constrained DDSCAT simulations
allow one to better understand the variability of the measured aerosol optical
properties in ambient air and to define benchmark biases due to different
approximations in aerosol parametrization. |
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