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| Titel |
Characterization of satellite-based proxies for estimating nucleation mode particles over South Africa |
| VerfasserIn |
A.-M. Sundström, A. Nikandrova, K. Atlaskina, T. Nieminen, V. Vakkari, L. Laakso, J. P. Beukes, A. Arola, P. G. Van Zyl, M. Josipovic, A. D. Venter, K. Jaars, J. J. Pienaar, S. Piketh, A. Wiedensohler, E. K. Chiloane, G. de Leeuw, M. Kulmala  |
| 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 ; 15, no. 9 ; Nr. 15, no. 9 (2015-05-04), S.4983-4996 |
| Datensatznummer |
250119690
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| Publikation (Nr.) |
 copernicus.org/acp-15-4983-2015.pdf |
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| Zusammenfassung |
| Proxies for estimating nucleation mode number concentrations and further
simplification for their use with satellite data have been presented in
Kulmala et al. (2011). In this paper we discuss the underlying assumptions
for these simplifications and evaluate the resulting proxies over an area in
South Africa based on a comparison with a suite of ground-based measurements
available from four different stations. The proxies are formulated in terms
of sources (concentrations of precursor gases (NO2 and SO2) and
UVB radiation intensity near the surface) and a sink term related to
removal of the precursor gases due to condensation on pre-existing aerosols.
A-Train satellite data are used as input to compute proxies. Both the input
data and the resulting proxies are compared with those obtained from
ground-based measurements. In particular, a detailed study is presented on
the substitution of the local condensation sink (CS) with satellite aerosol
optical depth (AOD), which is a column-integrated parameter. One of the main
factors affecting the disagreement between CS and AOD is the presence of
elevated aerosol layers. Overall, the correlation between proxies calculated
from the in situ data and observed nucleation mode particle number
concentrations (Nnuc) remained low. At the time of the satellite
overpass (13:00–14:00 LT) the highest correlation is observed for SO2/CS
(R2 = 0.2). However, when the proxies are calculated using satellite
data, only NO2/AOD showed some correlation with Nnuc
(R2 = 0.2). This can be explained by the relatively high uncertainties
related especially to the satellite SO2 columns and by the positive
correlation that is observed between the ground-based SO2 and NO2
concentrations. In fact, results show that the satellite NO2 columns
compare better with in situ SO2 concentration than the satellite
SO2 column. Despite the high uncertainties related to the proxies
calculated using satellite data, the proxies calculated from the in situ
data did not better predict Nnuc. Hence, overall
improvements in the formulation of the proxies are needed. |
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