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| Titel |
Climatology of aerosol optical properties and black carbon mass absorption cross section at a remote high-altitude site in the western Mediterranean Basin |
| VerfasserIn |
M. Pandolfi, A. Ripoll, X. Querol, A. Alastuey |
| 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 ; 14, no. 12 ; Nr. 14, no. 12 (2014-06-27), S.6443-6460 |
| Datensatznummer |
250118843
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| Publikation (Nr.) |
 copernicus.org/acp-14-6443-2014.pdf |
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| Zusammenfassung |
| Aerosol light scattering (σsp), backscattering
(σbsp) and absorption (σap)
were measured at Montsec (MSC; 42°3' N, 0°44' E, 1570 m a.s.l.), a remote
high-altitude site in the western Mediterranean Basin. Mean (±SD)
σsp, σbsp and σap were
18.9 ± 20.8, 2.6 ± 2.8 and 1.5 ± 1.4 Mm−1,
respectively at 635 nm during the period under study (June 2011–June 2013). Mean
values of single-scattering albedo (SSA, 635 nm), the scattering
Ångström exponent (SAE, 450–635 nm), backscatter-to-scatter ratio
(B / S, 635 nm), asymmetry parameter (g, 635 nm), black carbon mass absorption
cross section (MAC, 637 nm) and PM2.5 mass scattering cross section
(MSCS, 635 nm) were 0.92 ± 0.03, 1.56 ± 0.88, 0.16 ± 0.09,
0.53 ± 0.16, 10.9 ± 3.5 m2 g−1 and
2.5 ± 1.3 m2 g−1,
respectively. The scattering measurements performed at MSC were in the
medium/upper range of values reported by Andrews et al. (2011) for other
mountaintop sites in Europe due to the frequent regional recirculation
scenarios (SREG) and Saharan dust episodes (NAF) occurring mostly in
spring/summer and causing the presence of polluted layers at the MSC
altitude. However, the development of upslope winds and the possible
presence of planetary boundary layer air at MSC altitude in summer may also
have contributed to the high scattering observed. Under these summer
conditions no clear diurnal cycles were observed for the measured extensive
aerosol optical properties (σsp, σbsp
and σap). Conversely, low σsp and σap at MSC were
measured during Atlantic advections (AA) and winter regional anticyclonic
episodes (WREG) typically observed during the cold season in the western
Mediterranean. Therefore, a season-dependent decrease in the magnitude of
aerosol extensive properties was observed when MSC was in the free
troposphere, with the highest free-troposphere vs. all-data difference observed in winter and the lowest
in spring/summer. The location of MSC station allowed for a reliable
characterization of aerosols as a function of the main synoptic meteorological
patterns. The SAE was the lowest during NAF and showed an inverse
correlation with the outbreak intensity, indicating a progressive shift
toward larger particles. Moreover, the strength of NAF episodes in the
region led to a slope of the scattering vs. absorption relationship among the
lowest reported for other mountaintop sites worldwide, indicating that MSC
was dominated by dust aerosols at high aerosol loading. As a consequence,
SSA showed a nearly monotonic increase with increasing particle
concentration and scattering. The SAE was the highest during SREG, indicating
the presence of polluted layers dominated by smaller particles.
Correspondingly, the asymmetry parameter was lower under SREG compared with
NAF. The MAC and MSCS were significantly higher during NAF and SREG compared
to AA and WREG, indicating an increase of absorption and scattering
efficiencies associated with the summer polluted scenarios. The optical
measurements performed at the MSC remote site were compared with those
simultaneously performed at a regional background station in the western
Mediterranean Basin located at around 700 m a.s.l. upstream of the MSC station. |
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