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| Titel |
One year of Raman lidar observations of free-tropospheric aerosol layers over South Africa |
| VerfasserIn |
E. Giannakaki, A. Pfüller, K. Korhonen, T. Mielonen, L. Laakso, V. Vakkari, H. Baars, R. Engelmann, J. P. Beukes, P. G. Van Zyl, M. Josipovic, P. Tiitta, K. Chiloane, S. Piketh, H. Lihavainen, K. E. J. Lehtinen, M. Komppula |
| 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. 10 ; Nr. 15, no. 10 (2015-05-19), S.5429-5442 |
| Datensatznummer |
250119734
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| Publikation (Nr.) |
 copernicus.org/acp-15-5429-2015.pdf |
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| Zusammenfassung |
| Raman lidar data obtained over a 1 year period has been analysed in
relation to aerosol layers in the free troposphere over the Highveld in
South Africa. In total, 375 layers were observed above the boundary layer
during the period 30 January 2010 to 31 January 2011. The seasonal behaviour
of aerosol layer geometrical characteristics, as well as intensive and
extensive optical properties were studied. The highest centre heights of
free-tropospheric layers were observed during the South African spring (2520 ± 970 m a.g.l., also elsewhere). The geometrical layer depth was found
to be maximum during spring, while it did not show any significant
difference for the rest of the seasons. The variability of the analysed
intensive and extensive optical properties was high during all seasons.
Layers were observed at a mean centre height of 2100 ± 1000 m with an
average lidar ratio of 67 ± 25 sr (mean value with 1 standard
deviation) at 355 nm and a mean extinction-related Ångström exponent
of 1.9 ± 0.8 between 355 and 532 nm during the period under study.
Except for the intensive biomass burning period from August to October, the
lidar ratios and Ångström exponents are within the range of previous
observations for urban/industrial aerosols. During Southern Hemispheric
spring, the biomass burning activity is clearly reflected in the optical
properties of the observed free-tropospheric layers. Specifically, lidar
ratios at 355 nm were 89 ± 21, 57 ± 20, 59 ± 22
and 65 ± 23 sr during spring (September–November), summer (December–February), autumn (March–May) and winter (June–August),
respectively. The extinction-related Ångström exponents between 355
and 532 nm measured during spring, summer, autumn and winter were 1.8 ± 0.6, 2.4 ± 0.9, 1.8 ± 0.9 and 1.8 ± 0.6,
respectively. The mean columnar aerosol optical depth (AOD) obtained from
lidar measurements was found to be 0.46 ± 0.35 at 355 nm and 0.25 ± 0.2 at 532 nm. The contribution of free-tropospheric aerosols on the
AOD had a wide range of values with a mean contribution of 46%. |
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