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| Titel |
Brown carbon: a significant atmospheric absorber of solar radiation? |
| VerfasserIn |
Y. Feng, V. Ramanathan, V. R. Kotamarthi |
| 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 ; 13, no. 17 ; Nr. 13, no. 17 (2013-09-02), S.8607-8621 |
| Datensatznummer |
250085661
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| Publikation (Nr.) |
 copernicus.org/acp-13-8607-2013.pdf |
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| Zusammenfassung |
| Several recent observational studies have shown organic
carbon aerosols to be a significant source of absorption of solar radiation.
The absorbing part of organic aerosols is referred to as "brown" carbon
(BrC). Using a global chemical transport model and a radiative transfer
model, we estimate for the first time the enhanced absorption of solar
radiation due to BrC in a global model. The simulated wavelength dependence
of aerosol absorption, as measured by the absorption Ångström exponent (AAE), increases
from 0.9 for non-absorbing organic carbon to 1.2 (1.0) for strongly
(moderately) absorbing BrC. The calculated AAE for the strongly absorbing
BrC agrees with AERONET spectral observations at 440–870 nm over most
regions but overpredicts for the biomass burning-dominated South America and
southern Africa, in which the inclusion of moderately absorbing BrC has
better agreement. The resulting aerosol absorption optical
depth increases by
18% (3%) at 550 nm and 56% (38%) at 380 nm for strongly
(moderately) absorbing BrC. The global simulations suggest that the strongly
absorbing BrC contributes up to +0.25 W m−2 or 19% of the
absorption by anthropogenic aerosols, while 72% is attributed to black
carbon, and 9% is due to sulfate and non-absorbing organic aerosols
coated on black carbon. Like black carbon, the absorption of BrC (moderately
to strongly) inserts a warming effect at the top of the atmosphere (TOA)
(0.04 to 0.11 W m−2), while the effect at the surface is a reduction
(−0.06 to −0.14 W m−2). Inclusion of the strongly absorption of BrC
in our model causes the direct radiative forcing (global mean) of organic
carbon aerosols at the TOA to change from cooling (−0.08 W m−2) to
warming (+0.025 W m−2). Over source regions and above clouds, the
absorption of BrC is higher and thus can play an important role in
photochemistry and the hydrologic cycle. |
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