 |
| Titel |
Aerosol optical properties at Lampedusa (Central Mediterranean). 1. Influence of transport and identification of different aerosol types |
| VerfasserIn |
G. Pace, A. Sarra, D. Meloni, S. Piacentino, P. Chamard |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 6, no. 3 ; Nr. 6, no. 3 (2006-03-02), S.697-713 |
| Datensatznummer |
250003517
|
| Publikation (Nr.) |
 copernicus.org/acp-6-697-2006.pdf |
|
|
|
|
|
| Zusammenfassung |
| Aerosol optical depth and Ångström exponent were obtained from multi
filter rotating shadowband radiometer (MFRSR) observations carried out at
the island of Lampedusa, in the Central Mediterranean, in the period July
2001–September 2003. The average aerosol optical depth at 495.7 nm, τ,
is 0.24±0.14; the average Ångström exponent, α, is
0.86±0.63. The observed values of τ range from 0.03 to 1.13, and
the values of α vary from −0.32 to 2.05, indicating a large
variability in aerosol content and size. In cloud-free conditions, 36% of
the airmasses come from Africa, 25% from Central-Eastern Europe, and
19% from Western France, Spain and the North Atlantic. In summer, 42%
of the airmasses is of African origin. In almost all cases African aerosols
display high values of τ and low values of α, typical of
Saharan dust (average values of τ and α are 0.36 and 0.42,
respectively). Particles originating from Central-Eastern Europe show
relatively large average values of τ and α (0.23 and 1.5,
respectively), while particles from Western France, Spain and the North
Atlantic show the lowest average values of τ (0.15), and relatively
small values of α (0.92). Intermediate values of α are often
connected with relatively fast changes of the airmass originating sector,
suggesting the contemporary presence of different types of particles in the
air column. Clean marine conditions are rare at Lampedusa, and are generally
associated with subsidence of the airmasses reaching the island. Average
values of τ and α for clean marine conditions are 0.11 and
0.86, respectively. The largest values of α (about 2) were observed
in August 2003, when large scale forest fires in Southern Europe produced
consistent amounts of fine combustion particles, that were transported to
the Central Mediterranean by a persistent high pressure system over Central
Europe. Smoke particles in some cases mix with desert dust, producing
intermediate values of α. The seasonal distribution of the
meteorological patterns over the Mediterranean, the efficiency of the
aerosol production mechanisms, and the variability of the particles'
residence time produce a distinct seasonal cycle of aerosol optical depths
and Ångström exponent values. Particles originating from all sectors
show a summer maximum in aerosol optical depth. The summer increase in
optical depth for European aerosols is linked with an increment in the
values of α, that indicates an enhancement in the number of fine
particles. The summer maximum of τ for African particles is associated
with a weak reduction in the Ångström exponent, suggesting an
increase in the total number of particles and a relatively more intense
transport of large particles. The observations were classified according to
the aerosol optical properties, and two main classes have been identified:
desert dust and biomass burning/urban-industrial aerosols. Values of τ
and α averaged over the whole observing period are 0.37 and 0.15 for
desert dust, and 0.27 and 1.77 for urban-industrial/biomass burning
aerosols. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|