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| Titel |
Black carbon or brown carbon? The nature of light-absorbing carbonaceous aerosols |
| VerfasserIn |
M. O. Andreae, A. Gelencsér |
| 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 ; 6, no. 10 ; Nr. 6, no. 10 (2006-07-28), S.3131-3148 |
| Datensatznummer |
250004021
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| Publikation (Nr.) |
 copernicus.org/acp-6-3131-2006.pdf |
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| Zusammenfassung |
| Although the definition and measurement techniques for atmospheric "black
carbon" ("BC") or "elemental carbon'' ("EC") have long been subjects
of scientific controversy, the recent discovery of light-absorbing carbon
that is not black ("brown carbon, Cbrown") makes it imperative to
reassess and redefine the components that make up light-absorbing
carbonaceous matter (LAC) in the atmosphere. Evidence for the atmospheric
presence of Cbrown comes from (1) spectral aerosol light absorption
measurements near specific combustion sources, (2) observations of spectral
properties of water extracts of continental aerosol, (3) laboratory studies
indicating the formation of light-absorbing organic matter in the
atmosphere, and (4) indirectly from the chemical analogy of aerosol species
to colored natural humic substances. We show that brown carbon may severely
bias measurements of "BC" and "EC" over vast parts of the troposphere,
especially those strongly polluted by biomass burning, where the mass
concentration of Cbrown is high relative to that of soot carbon.
Chemical measurements to determine "EC" are biased by the refractory
nature of Cbrown as well as by complex matrix interferences. Optical
measurements of "BC" suffer from a number of problems: (1) many of the
presently used instruments introduce a substantial bias into the
determination of aerosol light absorption, (2) there is no unique conversion
factor between light absorption and "EC" or "BC" concentration in
ambient aerosols, and (3) the difference in spectral properties between the
different types of LAC, as well as the chemical complexity of Cbrown,
lead to several conceptual as well as practical complications. We also
suggest that due to the sharply increasing absorption of Cbrown towards
the UV, single-wavelength light absorption measurements may not be adequate
for the assessment of absorption of solar radiation in the troposphere. We
discuss the possible consequences of these effects for our understanding of
tropospheric processes, including their influence on UV-irradiance,
atmospheric photochemistry and radiative transfer in clouds. |
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