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| Titel |
Reducing uncertainties associated with filter-based optical measurements of light absorbing carbon particles with chemical information |
| VerfasserIn |
J. E. Engström, C. Leck |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 4, no. 8 ; Nr. 4, no. 8 (2011-08-02), S.1553-1566 |
| Datensatznummer |
250002074
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| Publikation (Nr.) |
 copernicus.org/amt-4-1553-2011.pdf |
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| Zusammenfassung |
The presented filter-based optical method for determination of
soot (light absorbing carbon or Black Carbon, BC) can be implemented in the
field under primitive conditions and at low cost. This enables researchers
with small economical means to perform monitoring at remote locations,
especially in the Asia where it is much needed.
One concern when applying filter-based optical measurements of BC is that
they suffer from systematic errors due to the light scattering of
non-absorbing particles co-deposited on the filter, such as inorganic salts
and mineral dust. In addition to an optical correction of the non-absorbing
material this study provides a protocol for correction of light scattering
based on the chemical quantification of the material, which is a novelty. A
newly designed photometer was implemented to measure light transmission on
particle accumulating filters, which includes an additional sensor recording
backscattered light. The choice of polycarbonate membrane filters avoided
high chemical blank values and reduced errors associated with length of the
light path through the filter.
Two protocols for corrections were applied to aerosol samples collected at
the Maldives Climate Observatory Hanimaadhoo during episodes with either
continentally influenced air from the Indian/Arabian subcontinents (winter
season) or pristine air from the Southern Indian Ocean (summer monsoon). The
two ways of correction (optical and chemical) lowered the particle light
absorption of BC by 63 to 61 %, respectively, for data from the Arabian Sea
sourced group, resulting in median BC absorption coefficients of 4.2 and 3.5
Mm−1. Corresponding values for the South Indian Ocean data were 69
and 97 % (0.38 and 0.02 Mm−1). A comparison with other studies in
the area indicated an overestimation of their BC levels, by up to two orders
of magnitude. This raises the necessity for chemical correction protocols on
optical filter-based determinations of BC, before even the sign on the
radiative forcing based on their effects can be assessed. |
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