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| Titel |
Exploiting simultaneous observational constraints on mass and absorption to estimate the global direct radiative forcing of black carbon and brown carbon |
| VerfasserIn |
X. Wang, C. L. Heald, D. A. Ridley, J. P. Schwarz, J. R. Spackman, A. E. Perring, H. Coe, D. Liu, A. D. Clarke |
| 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 ; 14, no. 20 ; Nr. 14, no. 20 (2014-10-20), S.10989-11010 |
| Datensatznummer |
250119108
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| Publikation (Nr.) |
 copernicus.org/acp-14-10989-2014.pdf |
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| Zusammenfassung |
| Atmospheric black carbon (BC) is a leading climate warming agent, yet
uncertainties on the global direct radiative forcing (DRF) remain large.
Here we expand a global model simulation (GEOS-Chem) of BC to include the
absorption enhancement associated with BC coating and separately treat both
the aging and physical properties of fossil-fuel and biomass-burning BC. In
addition we develop a global simulation of brown carbon (BrC) from both
secondary (aromatic) and primary (biomass burning and biofuel) sources. The
global mean lifetime of BC in this simulation (4.4 days) is substantially
lower compared to the AeroCom I model means (7.3 days), and as a result,
this model captures both the mass concentrations measured in near-source
airborne field campaigns (ARCTAS, EUCAARI) and surface sites within 30%,
and in remote regions (HIPPO) within a factor of 2. We show that the new
BC optical properties together with the inclusion of BrC reduces the model
bias in absorption aerosol optical depth (AAOD) at multiple wavelengths by
more than 50% at AERONET sites worldwide. However our improved model
still underestimates AAOD by a factor of 1.4 to 2.8 regionally, with the largest
underestimates in regions influenced by fire. Using the RRTMG model
integrated with GEOS-Chem we estimate that the all-sky top-of-atmosphere DRF
of BC is +0.13 Wm−2 (0.08 Wm−2 from anthropogenic sources and
0.05 Wm−2 from biomass burning). If we scale our model to match AERONET
AAOD observations we estimate the DRF of BC is +0.21 Wm−2, with an
additional +0.11 Wm−2 of warming from BrC. Uncertainties in size,
optical properties, observations, and emissions suggest an overall
uncertainty in BC DRF of −80%/+140%. Our estimates are at the lower
end of the 0.2–1.0 Wm−2 range from previous studies, and substantially
less than the +0.6 Wm−2 DRF estimated in the IPCC 5th Assessment
Report. We suggest that the DRF of BC has previously been overestimated due
to the overestimation of the BC lifetime (including the effect on the
vertical profile) and the incorrect attribution of BrC absorption to BC. |
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