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| Titel |
Modelling the optical and radiative properties of freshly emitted light absorbing carbon within an atmospheric chemical transport model |
| VerfasserIn |
M. Kahnert |
| 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 ; 10, no. 3 ; Nr. 10, no. 3 (2010-02-08), S.1403-1416 |
| Datensatznummer |
250008052
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| Publikation (Nr.) |
 copernicus.org/acp-10-1403-2010.pdf |
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| Zusammenfassung |
| Light absorbing carbon (LAC) aerosols have a complex, fractal-like aggregate
structure. Their optical and radiative properties are notoriously difficult to model, and
approximate methods may introduce large errors both in the interpretation of aerosol remote
sensing observations, and in quantifying the direct radiative forcing effect of LAC. In this
paper a numerically exact method for solving Maxwell's equations is employed for computing the
optical properties of freshly emitted, externally mixed LAC aggregates. The computations are
performed at wavelengths of 440 nm and 870 nm, and they cover the entire size range
relevant for modelling these kinds of aerosols. The method for solving the electromagnetic
scattering and absorption problem for aggregates proves to be sufficiently stable and fast
to make accurate multiple-band computations of LAC optical properties feasible. The results
from the electromagnetic computations are processed such that they can readily be integrated
into a chemical transport model (CTM), which is a prerequisite for constructing robust
observation operators for chemical data assimilation of aerosol optical observations. A case
study is performed, in which results obtained with the coupled optics/CTM model are employed
as input to detailed radiative transfer computations at a polluted European location. It is
found that the still popular homogeneous sphere approximation significantly underestimates
the radiative forcing at top of atmosphere as compared to the results obtained with the
aggregate model. Notably, the LAC forcing effect predicted with the aggregate model is less
than that one obtains by assuming a prescribed mass absorption cross section for LAC. |
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