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| Titel |
On the attribution of black and brown carbon light absorption using the Ångström exponent |
| VerfasserIn |
D. A. Lack, J. M. Langridge |
| 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. 20 ; Nr. 13, no. 20 (2013-10-31), S.10535-10543 |
| Datensatznummer |
250085777
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| Publikation (Nr.) |
 copernicus.org/acp-13-10535-2013.pdf |
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| Zusammenfassung |
| The absorption Ångström exponent (AAE) of externally mixed black
carbon (BCExt), or BC internally mixed with non-absorbing
material (BCInt), is often used to determine the contribution of
brown carbon (BrC) light absorption at short visible wavelengths. This
attribution method contains assumptions with uncertainties that have not been
formally assessed. We show that the potential range of AAE for
BCExt (or BCInt) in the atmosphere can reasonably
lead to +7% to −22% uncertainty in BCExt (or
BCInt) absorption at short wavelengths derived from measurements
made at longer wavelengths, where BrC is assumed not to absorb light. These
uncertainties propagate to errors in the attributed absorption of BrC. For
uncertainty in attributed BrC absorption to be ≤ ± 33%,
23% to 41% of total absorption must be sourced from BrC. These
uncertainties would be larger if absorption by dust were also to be
considered due to additional AAE assumptions. For data collected during a
biomass-burning event, the mean difference between measured and AAE
attributed BrC absorption was found to be 34% – an additional
uncertainty in addition to the theoretical uncertainties presented. In light
of the potential for introducing significant and poorly constrained errors,
we caution against the universal application of the AAE method for
attributing BrC absorption. |
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